Nahla S. Barakat, Ph.D
King Saud University
Dept. of Pharmaceutics
First Term
1432-2011
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Liquid dosage forms
Colloid
Disperse system: suspension, emulsion
Liposome and nanoparticles
Aerosols
Drug stability
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Solution is a homogenous mixture composed of two or
more substances. In such a mixture, a solute is dissolved in
another substance, known as a solvent. A common
example is a solid ,such as salt or sugar ,dissolved in
water ,a liquid.
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Gases may dissolve in liquids, for example:carbon dioxide
or oxygen in water.
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Liquids may dissolve in other liquids. Gases can combine
with other gases to form mixtures, rather than solutions.
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Possible Types of Solutions
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solid in solid e.g. brass
solid in liquid e.g. sugar in water
solid in gas e.g. mothball in air
liquid in solid e.g. dental amalgam
liquid in liquid e.g. ethanol in water
liquid in gas e.g. water in air
gas in solid e.g. hydrogen in palladium
gas in liquid e.g. O2 in water
gas in gas e.g. oxygen in nitrogen
Of the nine possible types of solutions, you are
probably most familiar with those in which the
solvent is a liquid, especially those in which the
solvent is water.
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1.
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Liquids are easier to swallow
A drug must be in solution before it can be absorbed
A solution is an homogenous system, the drug will be
uniformly distributed throughout the preparation
Some drugs can irritate the gastric mucosa if localized in
one area. Irritation is reduced by administration of a
solution of the drug
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Liquids are bulky and inconvenient to transport and store
The stability of ingredients in aqueous solution is often poor
than in solid dosage form
Solution provide suitable media for the growth of microorganisms and may require the addition of preservative
Accurate dose measuring depends on the ability of patient to
measure the dose
The taste of a drug is always pronounced when it in solution
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Aqueous solutions Solutions that contain water as the solvent
are called aqueous solutions. For example, sugar in water,
carbon dioxide in water, etc .
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Non-aqueous solutions Solutions that contain a solvent
other than water are called non-aqueous solutions. Ether,
benzene, petrol, carbon tetrachloride etc., are some common
solvents.or
example,
sulphur
in
carbon
disulphide,
naphthalene in benzene, etc .
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Concentrated solutions and dilute solutions
Between two solutions, the solute quantity may be relatively
more or less.
The solution that has a greater proportion of solute is said to
be more concentrated than the other that has a lesser
proportion. If the proportion of solute is less, the solution is
said to be dilute .
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Saturated Solution
A solution in which no more solute can be dissolved at a given
temperature is called a saturated solution
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Unsaturated solution
A solution in which more solute can be dissolved at a given
temperature is called an unsaturated solution.
A given solution that is saturated at a particular temperature
may become unsaturated when the temperature is increased.
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Solubility and Miscibility
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Different substances have different solubilities.
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Solubility refers to the maximum amount of a solute that
can be dissolved in an amount of solvent under specific
temperature and pressure conditions.
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A substance that cannot be dissolved in another (or does so
to a very limited extent) is said to be insoluble.
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 Solubility
 The solubility of a solute is the maximum quantity of solute
that can dissolve in a certain quantity of solvent or quantity of
solution at a specified temperature
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How do substances dissolve? Solvation - there is an interaction
between the solute and the solvent.
 The solute particles are usually surrounded by the solvent
particles. This process is called solvation.
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parts of solvent required
for 1 part of solute
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Very soluble
Freely soluble
Soluble
Sparingly soluble
Slightly soluble
Very slightly soluble
Practically insoluble
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1-10
10-30
30-100
100-1000
1000-10,000
 10,000
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Soluble
Group I and ammonium (NH4+) compounds
Nitrates
Acetates (Ethanoates)
Chlorides, bromides and iodides except: Silver (Ag+), Lead(II) (Pb2+),
Mercury(I) (Hg22+), Copper (Cu+)
Sulfates except: Silver (Ag+), Lead (Pb2+), Barium (II) (Ba2+),
Strontium(II) (Sr2+) and Calcium(II) (Ca2+)
Insoluble
Carbonates except Group I, ammonium (NH4+)
Sulfites except Group I and NH4+ compounds
Phosphates except Group I and NH4+ compounds
Hydroxides and Oxides except Group I, NH4+, Barium (Ba2+),
Strontium (Sr2+) and Thallium (Tl+)
Sulfides except Group I, Group II and NH4+ compoun
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Miscibility refers to the ability of a liquid to dissolve in
another in all proportions.
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Alcohols like methanol and ethanol are miscible with water.
There is no limit to the amount of these alcohols that can be
dissolved in water - they dissolve in all proportions. When the
amount of one liquid exceeds the other, their roles reverse. For
example if you add alcohol to water, alcohol is said to be
dissolved in water; however, if you add alcohol to the point
where its volume is greater than the volume of water, then
water becomes the solute and alcohol the solvent. When a
liquid does not dissolve in another to any extent, the liquids
are said to be immiscible .Oil and water are immiscible.
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Electrolytes and Non-Electrolytes
One way to distinguish between solutions that contain ions
and those that contain molecules is an electrical conductivity
test.
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A solution that conducts electrical current is said to be
electrolytic and the solute is called an electrolyte.
The sodium chloride solution is an electrolytic solution.
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The solute in a solution that does not conduct electrical current
is a non-electrolyte.
Examples include: sugar ,urea ,glycerol ,and
methylsulfonylmethane( MSM.
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Generally, dissociated ionic compounds are electrolytes
whereas dissolved molecular compounds are non-electrolytes.
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Concentrations are often given in terms of weight/volume. For
example, mg/L, or mg/100 mL (common clinical units), are
used. These units do not depend on knowledge of the molecular
structure of the measured substance.
A Molar Solution is an aqueous solution consisting of one mole
of a substance plus enough water to make one Liter of solution.
A Molal Solution is an aqueous solution consisting of one mole
of a substance plus 1 kg of water (usually very close to 1 L
water). The total volume may thus be more than 1 L.
Concentrations of ions are often given in Equivalents (or
milliequivalents, mEq) per Liter. The equivalents of an ion is
equal to the molarity times the number of charges per
molecule. Thus Equivalents is the measure of CHARGE
concentration.
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Mass per unit volume .This unit is typically milligrams per milliliter
(mg/mL) or milligrams per cubic centimeter (mg/cm 3 )
A useful note is that 1 mL = 1 cm3 and that cm 3 is sometimes referred to
as a "cc( "cubic centimeter.
Mass per unit volume is handy when discussing how soluble a material is
in water or a particular solvent. For example, "the solubility of Substance
X is 3 grams per liter."
Percent by Mass .Also called weight percent or percent by weight, this
is simply the mass of the solute divided by the total mass of the solution
and multiplied by 100%:
Percent by mass= mass of component
x 100
mass of solution
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Parts per million (PPM) .Parts per million works like percent by mass,
but is more convenient when there is only a small amount of solute
present.
PPM is defined as the mass of the component in solution divided by the
total mass of the solution multiplied by 106 (one million)
A solution with a concentration of 1 ppm has 1 gram of substance for
every million grams of solution.
Therefore, in general, one ppm implies one mg of solute per liter of
solution.
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Percentage (%)
% w/v 1g in 100 mL preparation
%v/v
1mL in 100 mL preparation
% w/w 1 g in 100 g preparation
Ratio strength:
weight in volume (1:1000 w/v= 1g constituent in 1000 mL
preparation)
volume in volume (1:1000 v/v = 1ml constituent in 1000 mL
preparation)
weight in weight (1:1000 w/w = 1 g constituent in 1000 g
preparation)
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FACTORS AFFECTING SOLUBILITY
There are three main factors that control solubility
of a solute.
(1) Temperature
(2) Nature of solute or solvent
(3) Pressure
(4) Particle size
(5) Stirring
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Solubility and Temperature Dependence
Electrostatic attractions between water and solid ions/molecules play
an important role in the solubility of solids in aqueous solutions.
However, there are other factors that also play an important role. One
of these factors is temperature.
Temperature is a direct result of the kinetic movement of the solution
molecules/ions. The higher the temperature the greater the kinetic
energy of the solution molecules.
The higher the kinetic energy of water molecules, the better the chance
they have of dislodging solid molecules and thereby getting them into
solution. This is so because the water molecules collide with the solid
and higher collision energies lead to more effective dislodgment and
thus solubility.
In a few instances (e.g., Ce2SO4) the solubility of the salt will decrease
with temperature.
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CASE I: Decrease in solubility with temperature:
If the heat given off in the dissolving process is
greater than the heat required to break apart the solid,
the net dissolving reaction is exothermic (energy
given off). The addition of more heat (increases
temperature) inhibits the dissolving reaction since
excess heat is already being produced by the reaction.
This situation is not very common where an increase
in temperature produces a decrease in solubility.
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CASE II: Increase in solubility with temperature:
If the heat given off in the dissolving reaction is less
than the heat required to break apart the solid, the
net dissolving reaction is endothermic (energy
required). The addition of more heat facilitates the
dissolving reaction by providing energy to break
bonds in the solid. This is the most common
situation where an increase in temperature
produces an increase in solubility for solids
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Solubility of Gases vs. Temperature:
The variation of solubility for a gas with temperature can be
determined by examining the graphic on the left.
As the temperature increases, the solubility of a gas decrease as
shown by the downward trend in the graph .
More gas is present in a solution with a lower temperature
compared to a solution with a higher temperature.
The reason for this gas solubility relationship with temperature is
very similar to the reason that vapor pressure increases with
temperature. Increased temperature causes an increase in kinetic
energy. The higher kinetic energy causes more motion in
molecules which break intermolecular bonds and escape from
solution.
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Nature of Solute and Solvent
• Nature of both the solute and the solvent affect the
solubility.
Substances with similar intermolecular attractive forces
tend to be soluble in one another. This generalization is
stated as "like dissolves like."
• Non polar solutes are soluble in non polar solvents; Polar
or ionic solutes are soluble in polar solvents
Liquids that are attracted by charged objects are composed
of polar molecules; those that are not attracted by a
charged body are non polar
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Nature of Solute and Solvent
Solute
Polar Solvent
Non-polar solvent
Polar
Soluble
Insoluble
Non-Polar
Insoluble
Soluble
Ionic
Soluble
Insoluble
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Molecular size
The larger the molecules of the solute are, the larger is their
molecular weight and their size.
It is more difficult for solvent molecules to surround bigger
molecules.
The larger particles are generally less soluble.
In the case of organic compounds the amount of carbon
"BRANCHING "will increase the solubility since more branching
will reduce the size (or volume) of the molecule and make it easier
to solvate the molecules with solvent .
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Pressure
The effect of pressure is observed only in the case of gases.
An increase in pressure increases of solubility of a gas in a
liquid.
For example carbon di oxide is filled in cold drink bottles (such
as coca cola, Pepsi 7up etc.)under pressure.
Stirring
Agitation makes the solute dissolves more rapidly because it brings
fresh solvent into contact with the surface of the solute. However,
agitation affects only the rate at which a solute dissolves. It cannot
influence the amount of solute that dissolves. An insoluble substance
will remain undissolved no matter how much the system is agitated.
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Diffusion layer model:
Simplest and most common theory for dissolution The process of
dissolution of solid particle in a liquid, in the absence of reactive or
chemical force Consists of two consecutive stages: STAGE 1:First is an
interfacial reaction that results in the liberation of solute molecules from
the solid phase. This involves a phase change so that molecules of solid
become molecules of solute in the solvent in which the crystal is
dissolving. The solution in contact with the solute will be
saturated(because it is in direct contact with undissolved solid. Its
concentration will be Cs , a saturated solution. In short solution of the
solute form a thin film or layer at the solid/liquid interface called as
stagnant layer or diffusion layer or boundary layer This step is usually
rapid. DIFFUSION LAYER MODEL
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STAGE 2: After this , the solute molecules must migrate through the
boundary layers surrounding the crystal to the bulk of the solution,at
which time its concentration will be Cb. This step involves the transfer
of these molecules away from the solid liquid interface into the bulk of
the liquid phase under the influence of diffusion or convection. This
step is slow step.
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BOUNDARY LAYERS
Boundary layers are static or slow moving layers of liquid that
surround all wetted solid surfaces.
The rate of flow of fluid over an even surface will be dependant
upon the distance from the surface.
The velocity, which will be almost zero at the surface , increases
with the increasing distance from the surface until the bulk of the
fluid is reached and the velocity becomes constant.
In short, the region over which differences in velocity are observed
is referred to as boundary layers.
Its depth is dependant upon the viscosity of the fluid and the rate of
flow in the bulk fluid.
If high viscosity and low flow rate then thick boundary.
If low viscosity and high flow rate then thin boundary.
Boundary layers arises because of the intermolecular forces between
the liquid molecules and solid surface.
They are important barrier for heat and mass transfer.
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Now, Mass transfer takes place more slowly trough these static or
slow moving layers ,which inhibit the movement of solute molecules
from the surface of the solid to the bulk of the solution. The
concentration of the solution in the boundary layers changes
therefore from being saturated (Cs) at the crystal surface to being
equal to that of the bulk of the solution (Cb) at its outmost limit.
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RATE LIMITING STEP
Like any reaction that involves consecutive stages, the overall
rate of dissolution will depend on whichever of this steps is the
slowest. Here the interfacial step-1 is rapid and step-2 is slower
and so the rate of dissolution will be determined by the rate of
slower step-2, of diffusion of dissolved solute across the static
boundary layers of liquid that exists at a solid liquid interface.
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FICK’S SECOND LOW OF DIFFUSION
Whitney equation based on Fick’s second low of
diffusion. The rate of diffusion will obey fick’s law of
diffusion, i.e the rate of change in concentration of
dissolved material with time it directly proportional to
the concentration difference between the two sides of
diffusion layer. i.e, dc/dt  ∆ C----------(1)
dc/dt = k x ∆C--------------(2)
where the constant k is the rate constant(sec-1) and ∆ C is
the difference in concentration of solution at solid
surface(Cs) and the bulk of the solution(Cb).
So, dc/dt = k(Cs-Cb)--------------(3)
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MODIFIED NOYES WHITNEY EQATION
It was developed to defined the dissolution from a single spherical
particle.
It is based on the Fick’s fist law of diffusion. The rate of mass transfer
of solute molecules or ions through a static diffusion layer (dm/dt) is
directly proportional to the surface area available for molecule or ionic
migration (A) ,
the concentration difference (Cs-Cb) across the boundary layer, is
inversely proportional to the thickness of the boundary layer (h).
Dm/dt= DAK (Cs-Cb)
Vh
Where, dm/dt =Rate of mass transfer, D=diffusion coefficient(m2/s)
A=surface area, Kw/o=water/oil partition coefficient of the drug,
(Cs-Cb)=concentration gradient, V=volume of dissolution media,
h=Thickness of boundary layer
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Non Sink condition
Above Equation represents first order dissolution process ,the driving
force for which is the concentration gradient (Cs-Cb). Under such a
situation , dissolution is said to be under non sink conditions. This is true
in case of in vitro dissolution in a limited dissolution medium.
Dissolution in such a situation slow down after sometime due to build up
in the concentration of drug in the bulk of solution .
Sink condition
The in vivo dissolution is always rapid than in vitro dissolution because
the moment the drug dissolves, it is absorbed into the systemic
circulation. As a result Cb=0 and dissolution is at its maximum. Thus,
under in vivo conditions, there is no concentration build up in the bulk of
the drug i.e Cs>>Cb and sink condition are maintained.
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Factor affecting in-vitro dissolution rate of solid in liquid
1] Diffusion Co-efficient - greater the value faster the dissolution - Affected
by viscosity of dissolution medium and size of diffusing molecules. Diffusion decreases as the viscosity of the dissolution medium increases.
2] Surface area
- Greater the surface area faster the dissolution Affected by:
1) Size of solid particles
– A1/Particle size.
Particle size will change during dissolution process, because large
particle will become smaller and small particles will disappear.
1) ) Dispersibility of powdered solid in dissolution medium.
- If particles tend to form coherent mass in the dissolution medium then
the surface area available for dissolution is reduced.This effect may be
overcome by addition of wetting agent.
1) Porosity of solid particle.
- Pores must be large enough to allow access of dissolution medium and
outward diffusion of dissolved solute molecules.
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3] Water oil partition co-efficient
Higher the value , more the hydrophiliciity and faster the dissolution in aqueous
fluid.
4] Concentration gradient
Greater the concentration gradient, faster the diffusion and drug dissolution.
Can be increased by increasing drug solubility and volume of dissolution media.
This is affected by:
4.1) Volume of dissolution media -If volume is small Cb will approach Cs, if
volume is large Cb may be negligible WRT Cs i.e apparent sink condition.
4.2) Temperature
-Dissolution may be an exothermic or endothermic process. According to
thermodynamic equation, G= H- T S
The change in the Gibbs free energy of the system that occurs during a reaction
is therefore equal to the change in the enthalpy of the system minus the change
in the product of the temperature times the entropy of the system.
∆G = ∆H - ∆(TS)
If the reaction is run at constant temperature, this equation can be written as
follows.
∆G = ∆H - T∆S
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When ∆H is positive, the dissolution process is endothermic i.e heat is
absorbed when dissolution occurs.
In endothermic process, a rise in temperature will lead to an increase in
the solubility of the solid with positive heat of solution.
-In exothermic dissolution, an increase in temp will lead to decrease in
solubility. Solubility curve are often used to describe the effect of
temperature.
For e.g. sodium Sulphate exist as the decahydrate form up to 32.5°C,
and its dissolution in water is endothermic process. Its solubility
therefore increases with rise in temp up to 32.5°C. Above this temp it is
converted in to anhydrous form and the dissolution of this is an
Exothermic process. The solubility therefore exhibits a change from
+ve to –ve slope as the temp exceed the transition value.
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4.3) Nature of dissolution media
A- Co solvents
-Some mixtures are used to increase the solubility of solid. This is
achieved by using co solvents such as ethanol or propylene glycol, which
are miscible with water and which act as better solvent for solute.
-For e.g..the aqueous solubility of metronidazole is about 100mg in 10
ml. The solubility of this drug can be increased by the incorporation of
water miscible co solvent to the 500mg in 10 ml.
B- pH
-If the pH of the solution of either weakly acidic drug or a salt of a drug is
reduced then the proportion of unionized molecules in the solution
increases. -Precipitation may occur because the solubility of the
unionized species is less than that of ionized form.
In case of solution of weakly basic drugs or their salts, precipitation is
favoured by an increase in pH.
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4.4) Molecular structure of solid.
-A small change in the molecular structure of the compound can have a
marked effect on its solubility in a given liquid For e.g.. The introduction of
hydrophilic hydroxyl group can produce a large improvement in water
solubility as evidenced by more than 100 fold difference in the solubility of
phenol and benzene.
-The conversion of weak acid to its sodium salt led to a much greater degree
of ionic dissociation of the compound.A specific e.g. of this effect is provided
by comparison of aqueous solubility of salicylic acid and its sodium salt,which
are 1:550 and 1:1 respectively.
5] Thickness of stagnant layer
more the thickness , lesser the diffusion and drug dissolution.
Can be decreased by increasing agitation.
Affected by degree of agitation , which depends on speed of stirring and
shaking , shape , size , and position of stirrer , volume of dissolution medium ,
shape and size of container, viscosity of dissolution medium
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To obtained good in vitro in vivo dissolution rate correlation, the in vitro
dissolution must be carried under sink condition, this can be achieved by:
 Bathing the dissolving solid in fresh solvent from time to time.
Increasing the volume of dissolution.
Removing the drug by partitioning it from the aqueous phase of the
dissolution fluid into an organic phase placed either above or below the
dissolution fluid –for example ,hexane or chloroform.
Adding a water miscible solvent such as alcohol to the dissolution fluid,
or By adding selected adsorbents to remove the dissolved drug.
The in vitro sink conditions are so maintained that Cb is always less
than 10% of CS
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Problem 1:
Calculate the dissolution rate of a hydrophobic drug having the following
physicochemical characteristics:
surface area = 2.5 x 103 cm2
saturated solubility = 0.35 mg/mL (at room temperature)
diffusion coefficient = 1.75 x 10-7 cm2/s
thickness of diffusion layer = 1.25 µm
[Note: need to convert to cm,
so 1 µm = 1 x 10-4 cm and 1.25 x 10-4 cm]
conc of drug in bulk = 2.1 x 10-4 mg/mL
dM/dt = DS(CS-Cb) / h
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What is surface tension?
Surface tension is a property of the surface of a liquid that allows
it to resist an external force
Surface tension is a measurement of the cohesive energy present
at an interface.
The cohesive forces among the liquid molecules are responsible
for this phenomenon of surface tension. In the bulk of the liquid,
each molecule is pulled equally in every direction by neighboring
liquid molecules, resulting in a net force of zero. The molecules at
the surface do not have other molecules on all sides of them and
therefore are pulled inwards. This creates some internal pressure
and forces liquid surfaces to contract to the minima
Surface tension is typically measured in dynes/cm, the force in
dynes required to break a film of length 1 cm. Equivalently, it can
be stated as surface energy in ergs per square centimeter. Water
at 20°C has a surface tension of 72.8 dynes/cm compared to 22.3
for ethyl alcohol and 465 for mercury.
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• Walking on water
• Small insects such as the water strider can walk on water because their
weight is not enough to penetrate the surface.
• Soaps and detergents
• help the cleaning of clothes by lowering the surface tension of the
water so that it more readily soaks into pores and soiled areas.
• Floating a needle
• If carefully placed on the surface, a small needle can be made to float
on the surface of water even though it is several times as dense as
water. If the surface is agitated to break up the surface tension, then
needle will quickly sink.
• Surface tension disinfectants
• Disinfectants are usually solutions of low surface tension. This allow
them to spread out on the cell walls of bacteria and disrupt them. One
such disinfectant, S.T.37, has a name which points to its low surface
tension compared to the 72 dynes/cm for water.
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• Surface tension is responsible for the shape of liquid
droplets. Although easily deformed, droplets of water tend
to be pulled into a spherical shape by the cohesive forces
of the surface layer
• Cohesion and Surface Tension
• The cohesive forces between molecules down into a liquid
are shared with all neighboring atoms. Those on the
surface have no neighboring atoms above, and exhibit
stronger attractive forces upon their nearest neighbors on
the surface. This enhancement of the intermolecular
attractive forces at the surface is called surface tension.
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Adhesive Forces
Forces of attraction between a liquid and a solid surface are
called adhesive forces. The difference in strength between
cohesive forces and adhesive forces determine the behavior of a
liquid in contact with a solid surface.
Water does not wet waxed surfaces because the cohesive forces
within the drops are stronger than the adhesive forces between
the drops and the wax.
Water wets glass and spreads out on it because the adhesive
forces between the liquid and the glass are stronger than the
cohesive forces within the water.
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Surface tension is the energy required to stretch a unit change of a
surface area. Surface tension will form a drop of liquid to a sphere
since the sphere offers the smallest area for a definite volume.
Surface tension can be defined as
σ = Fs / l
(1)
where
σ = surface tension (N/m)
Fs = stretching force (N)
l = unit length (m)
Alternative Units
Alternatively, surface tension is typically measured in dynes/cm, which
is
the force in dynes required to break a film of length 1 cm
or as surface energy J/m2 or alternatively ergs per square centimeter.
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When liquid water is confined in a tube, its
surface (meniscus) has a concave shape
because water wets the surface and creeps
up the side.
Mercury does not wet glass - the cohesive forces
within the drops are stronger than the adhesive forces
between the drops and glass. When liquid mercury is
confined in a tube, its surface (meniscus) has a convex
shape because the cohesive forces in liquid mercury
tend to draw it into a drop.
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Capillary Action
Capillary action is the rise of a liquid that wets a tube up the inside of a small
diameter tube (i.e., a capillary) immersed in the liquid.
The liquid creeps up the inside of the tube (as a result of adhesive forces between
the liquid and the inner walls of the tube) until the adhesive and cohesive forces of
the liquid are balanced by the weight of the liquid.
The smaller the diameter of the tube, the higher the liquid rises.
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• Surface Tension of Water
• The surface tension of water is 72 dynes/cm at 25°C . It
would take a force of 72 dynes to break a surface film of
water 1 cm long. The surface tension of water decreases
significantly with temperature as shown in the graph. The
surface tension arises from the polar nature of the water
molecule. Hot water is a better cleaning agent because the
lower surface tension makes it a better "wetting agent" to
get into pores and fissures rather than bridging them with
surface tension. Soaps and detergents further lower the
surface tension.
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• The polar nature of water molecules allows them to bond to
each other in groups and is associated with the high surface
tension of water.
• The polar nature of the water molecule has many
implications. It causes water vapor at sufficient vapor
pressure to depart from the ideal gas law because of dipoledipole attractions. This can lead to condensation and
phenomena like cloud formation, fog, the dewpoint, etc. It
also has a great deal to do with the function of water as the
solvent of life in biological systems
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• Surface Tension and Bubbles
• The surface tension of water provides the necessary wall
tension for the formation of bubbles with water. The tendency
to minimize that wall tension pulls the bubbles into spherical
shapes (LaPlace's law).
• The pressure difference between the inside and outside of a
bubble depends upon the surface tension and the radius of the
bubble. The relationship can be obtained by visualizing the
bubble as two hemispheres and noting that the internal
pressure which tends to push the hemispheres apart is
counteracted by the surface tension acting around the
cirumference of the circle.
• For a bubble with two surfaces providing tension tension, the
pressure relationship is:
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• Capillary Action
• Capillary action is the result of adhesion and surface
tension. Adhesion of water to the walls of a vessel will
cause an upward force on the liquid at the edges and
result in a meniscus which turns upward. The surface
tension acts to hold the surface intact, so instead of just
the edges moving upward, the whole liquid surface is
dragged upward.
•
The smaller the diameter of the tube, the higher the liquid rises
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Influence of solute concentration
Solutes can have different effects on surface tension depending on their
structure:
Little or no effect, for example sugar
Increase surface tension, inorganic salts
Decrease surface tension progressively, alcohols
Decrease surface tension and, once a minimum is reached, no more
effect: surfactants
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Effect of Temperature
The surface tension of a liquid in contact with air or its own
vapour depends only on temperature and nature of liquid.
Surface tension decreases with raise of temperature.
It represents the variation of surface tension and surface
energy of water with temperature. Clearly the Surface tension
decreases with raise of high temperature. and becomes zero
at 374⁰C which is the critical temperature of water.
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• Effects of Solute
• If the solute is less soluble in liquid, the factors affecting
surface tension of liquid decreases. For example by mixing
soap, detergent powder or phenol in water, the surface tension
of water decreases but if the solute is very soluble in liquid, the
surface tension of liquid increases. For example if salt is mixed
in water, the surface tension of water increases.
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• Effect of Contamination
• The presence of dust, oil or grease on the surface of water, reduces the
surface tension of water.
• Factors affecting surface tension decreases with rise of temperature
and becomes zero at critical temperature. Critical temperature of water
is 374⁰C.
• The surface of a liquid acts like a stretched membrane and tends to
occupy the minimum surface area. This property of the liquid is called
the surface tension.
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 Surfactants
 Surface tension is visible in other common phenomena,
especially when surfactants are used to decrease it:
 Soap bubbles have very large surface areas with very little
mass. Bubbles in pure water are unstable. The addition of
surfactants, however, can have a stabilizing effect on the
bubbles (see Marangoni effect). Notice that surfactants
actually reduce the surface tension of water by a factor of
three or more.
 Emulsions are a type of solution in which surface tension
plays a role. Tiny fragments of oil suspended in pure water
will spontaneously assemble themselves into much larger
masses. But the presence of a surfactant provides a decrease
in surface tension, which permits stability of minute droplets
of oil in the bulk of water (or vice versa
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
An aqueous solution is a solution in which the solvent is
water.

As water is an excellent solvent as well as naturally abundant.

Substances that do not dissolve well in water are called
hydrophobic') water fearing') whereas those that do are known
as hydrophilic (Water-loving').

An example of a hydrophilic substance would be the sodium
chloride , ordinary table salt.
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Factors affecting solution stability:
Temperature
− Arrhenius equation:
k = Ae−Ea / RT
− Underlying assumption
• Reaction mechanism does not change as a function of
temperature, i.e., Ea is independent of T
• May not be valid for some reactions, especially the
complex reactions Factors
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Solvent
− pH of aqueous solvents
• Acid, base, and water catalyzed reactions, mostly hydrolysis
• Leading to various kinetic profiles: L, V, U
• More complex shapes of kinetic profiles if the compound has
(multiple)ionizable functionality
− Composition: medium effect on chemical reactions
• Non-traditional dosage forms: e.g. co-solvents, soft gel, lipid
based systems
Factors
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Light
• Oxygen
• Co-solutes
− Buffer salts: catalysis
− Surfactants: different environment in the micelles
− Complexation agents: different environment, e.g.
cyclodextrin
− Antioxidants and/or chelating agents
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Common Degradation Routes
• Solvolysis/hydrolysis
− Most frequently encountered hydrolysis – ester
− Typically pseudofirst order
− Intramolecular catalysis and steric factors
• Photolysis/oxidation
• Racemization
− May cause substantial decrease in biological activities: e.g.
Pilocarpine, tetracycline
• Others
− e.g. decarboxylation
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Aqueous solutions
Types of pharmaceutical water
Purified water, USP
Water for injection
Aromatic water
 Physiological compatibility
 Lack of toxicity
 Possesses a high dielectric constant
 ensuring the dissolution of a wide range of ionizable materials
 Lack of selectivity

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I- Some solvents for liquid preparations
 Alcohol
 The most useful solvent in pharmacy (orally and parenterally)
 It form hydroalcoholic mixture with water that dissolves both
alcohol-soluble and water-soluble substances
 It is miscible with water and can dissolve many waterinsoluble ingredients, including drug substances, flavorants,
preservatives.
 It is used as antimicrobial preservative (15%)
 Toxicity of ingested alcohol particularly for children.
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•
•
•
•
•
•
•
•
Diluted alcohol
Is prepared by mixing equal volumes of alcohol and purified
water (50%)
Alcohol, Rubbing
Alcohol rubbing compound
It contains about 70% ethyl alcohol by volume
It is employed as a rubefacient externally and as
soothing rub for bedridden patients, a germicide
for instruments
As vehicle for topical preparation
As skin cleanser before injection
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
Glycerol


It is a clear syrup liquid with sweet taste
It is miscible with water and alcohol
As solvent it is compatible with alcohol
It is used as a stabilizer and as auxiliary solvent
It has preservative qualities
It is used in internal preparations

Isopropyl rubbing alcohol

Is about 70% by volume isopropyl alcohol, with or without colour
additives, stabilizers and perfume oils
It is used externally as a rubefacient and soothing rub and for topical
products
It is less likely to be abused

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
Propylene glycol
A viscous liquid, miscible with water, glycerol and alcohol
It is substituted for glycerol in modern pharmaceutical
preparations
It is used for formulation of digoxin, diazepam, phenobarbital
injection
As diluent for ear drops
PEG 400
Is used as a solvent in topical solution
Used as co-solvent with alcohol and water
Can be used for extraction processes
In the formulation of veterinary solutions
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Ethyl ether
Used for extraction of crude drugs
It is used as a co-solvent with alcohol in some
collodions
It is not used for internal use
Liquid paraffin
It is unpleasant to use externally
It is used as a solvent for topical application of
drugs in emulsion formulations
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






Dimethylsulfoxide
It is used as a solvent for veterinary drugs
It is used for application to human skin
Miscellaneous solvents
Isopropyl myristate, isopropyl palmitate are solvent for
external use, cosmetics
Low viscous, lack of greasiness
Xylene is used in ear drops for human use to dissolve ear wax
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•
Buffers
Injection, eye drops and nasal drops should be buffered at pH 7.4
Ex: carbonates, citrates, phosphate, lactates, gluconates, tartarates, borates
(external)
•
Density modifier
Ex: dextrose
•
Isotonicity modifier
Ex: dextrose and sodium chloride
•
Viscosity enhancement
Low conc., of gelling agents can be used to increase the apparent viscosity of
the product
Ex: Povidone, Carbomer, Hydroxyethylcellulose
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•
Preservatives
Ex: parahydroxybenzoic acid esters (Parabens)
•
Reducing agent and antioxidants
Ex: sodium metabisulphite,
hydroxytoluene
•
butylated
hydroxyanisole
or
butylated
Sweetening agent
Ex: sucrose, polyhydric alcohols: sorbitol, mannitol,
artificial sweeteners: sodium or calcium salt of saccharin
• Flavours and perfumes
To mask the unpalatable taste, ex: fruit juices, aromatic oils, herps
•
Colours
To improve the attractiveness of the product and to enable ease of
identification
Ex: carotenoids, chlorophyll, riboflavines, coal tar dyes
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According to particular pharmaceutical solution’s use may be classified as:
• Oral
• Otic
• Ophthalmic
• Nasal
• Topical
According to the composition or use, solutions may be classified as :
• Aqueous solution containing sugar are termed syrups
• Sweetened hydroalcoholic solutions are termed elixirs
• Solution of aromatic materials are termed spirits
• Solutions prepared by extracting active constituents from crude drugs are
termed tinctures
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Dry mixtures for solution
Certain antibiotics have insufficient stability in aqueous
solution to meet extended shelf life periods
They are provided in dry powders or granules for reconstitution
before use
Once reconstituted, the solution remain stable for 7-14 days
depending on the condition of storage
Examples: Penicillin V Potasium for oral solution, USP
Cloxacillin Sodium for oral solution, USP
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Oral rehydration solutions
Are usually effective in treatment of diarrhea and mild volume depletion (510% of body weight). These are available OTC
+
+
Oral solution contains: 45mEq Na , 20 mEq K , 35 mEq CL , 30 mEq citrate,
25 g dextrose / 1 Liter
These formulations are available in liquid or powder packets form for
reconstitution
These products should not be mixed with milk or fruit juice
Oral colonic lavage solution
Used for preparation of the bowel for colonoscopy
Composed of oral solution of electrolytes with PEG-3350.
Before dispensing it to the patient, the solution is reconstituted with water,
creating an iso-osmotic solution. PEG is an osmotic agent in the GIT
 The formulation is as follows:
 PEG-3350; Sodium sulfate; sodium bicarbonate; sodium
chloride; potassium chloride 240 ml every 10 min (total 4 L).
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
In cooking, a syrup (from Arabic ‫ شراب‬sharab ,beverage, via Latin
siropus) is a thick ,viscous liquid ,containing a large amount of
dissolved sugars ,or sugar substitute with or without flavoring agents
and medicinal substances.

Syrup containing flavoring agents but not medicinal substances are
called nonmedicated or flavored vehicles (syrup):

Cherry syrup

Orange syrup

Raspberry syrup
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
The syrup are intended to serve as pleasant-tasting vehicles for medicinal
substances, consists of a concentrated or saturated solution of refined sugar
in distilled water.

The "simple syrup" of the British Pharmacopoeia is prepared by dissolving
85 g of refined sugar in purified water to make 100 mL of syrup. The
specific gravity of the syrup should be 1.313.

Flavoured syrups are made by adding flavouring matter to a simple syrup.
For instance ,syrupus aromaticus is prepared by adding certain quantities
of orange flavouring and cinnamon water to simple syrup. Similarly,
medicated syrups are prepared by adding medicaments to, or dissolving
them in, the simple syrup.
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•
•
•
•
•
•
•
•
As syrups can contain up to 85% of sugars, they are capable of resisting
bacterial growth by virtue of their osmotic effect.
Syrup, NF, also called simple syrup.
The amount of preservative required to protect a syrup against microbial
growth varies with the proportion of water available for growth
Preservative commonly used in syrups : benzoic acid 0.1-0.2%, sodium
benzoate 0.1-0.2%, parabens (0.1%)
To enhance the appeal of the syrup, a coloring agent that correlates with the
flavorant employed (green with mint, brown with chocolate).
Most syrups are flavored with synthetic flavorants or with naturally
occurring materials, such as volatile oils (orange oil), vanilin
Colorant to enhance the appeal of the syrup may be added
Sucrose-based syrup may be substituted by a polyol, such as sorbitol
solution USP, 64%
•
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
Examples of medicated syrup:

Analgesic
Anticholenergic
Antiemetics
Anticonvulsant
Antihistamine
Antiviral
Antitussives
Expectrorant
Bronchodilators
Fecal softener
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
An elixir (From Arabic, ‫ )اإلكسير‬are clear, sweetened
hydroalcoholic solutions intended for oral use and usually
flavored to enhance their palatability.

Non-medicated elixirs are employed as vehicles.

Elixirs are usually less sweet and less viscous than syrup.

In addition to alcohol and water, other solvents, such as
glycerol and propylene glycol are frequently employed in
elixirs as adjunctive solvents.
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90
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Elixirs are sweetened with sucrose, sorbitol, glycerol, and/or
artificial sweeteners
Most elixirs have coloring agents to enhance their appearance
Elixirs containing more than 10-12% alcohol are usually selfpreserving
Because of their usual content of volatile oils and alcohol,
elixirs should be stored in tight, light-resistant containers and
protected from excessive heat
Antihistamine Elixir: Diphenhydramine HCl
Analgesic Elixir: acetominophen
Cardiotonic Elixir: digoxin
Antispasmodic Elixir: hyoscyamine sulfate
Sedative Elixir: phenobarbital
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•
In medicine, a tincture is an alcoholic extract (e.g.
of leaves or other plant material) or solution of a
non-volatile
substance;
e.g.
of
iodine,
mercurochrome).
•
•
•
Tinctures contain alcohol in amounts ranging from
approx. 15-80%. The alcohol content protects
against microbial growth
Other solvent, such as glycerol, may be employed
Tincture must be tightly stopered and not exposed
to excessive temperature
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
Many tinctures must be stored in light-resistant containers
and protect from sunlight.

Some examples that were formerly common in medicine
include:
Tincture of Cannabis sativa
Tincture of Benzoin
Tincture of cantharides
Tincture of green soap( (which also contains lavender)
Tincture of guaiac
Tincture of iodine
Tincture of opium (laudanum)
Camphorated opium tincture (paregoric)
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


Tincture of iodine is often found in emergency
survival kits, used both to disinfect wounds and to
sanitize surface water for drinking.
When an alcohol solution is not desirable, Lugol's
iodine, an aqueous solution of iodine in potassium
iodide solution, or povidone iodine (Betadine), a
PVP solution, can be used.
Other names for Lugol's solution are I2KI (IodinePotassium Iodide); Markodine, Strong solution
(Systemic); Aqueous Iodine Solution BP.
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





A viscous preparation, usually for the relief of cough
It consists of a simple solution of the active agent in a high
concentration of sucrose
The syrup content has a demulcent action on the mucous
membranes of the throat
For diabetic use, the sucrose is replaced by sorbitol or
synthetic sweeteners
This type of product, should be sipped slowly and not be
diluted beforehand
It is administered in multiple of 5 mL
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Sodium Salicylate – 15 gr.
Sodium Bicarbonate – 30 gr.
Aromatic Spirit of Ammonia – 20 min.
Camphor water, up to – 1 oz.
For use in acute rheumatism and other
febrile conditions
Sodium Salicylate – 15 gr.
Sodium Bicarbonate – 30 gr.
Strong Solution of Ammonium Acetate – 30
min.
Compound Tincture of Cinchona – 20 min.
Syrup of Tolu – 1 dr.
Camphor water, up to – 1 oz.
Useful in Influenza.
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Topical solutions
•
Aluminum acetate (Burow’s solution)
•
•
Is colourless and has a faint acetous odor, is applied topically as an
astringent wash or wet dressing after dilution with 10 to 40 parts of water.
Used in various types of dermatological lotions, cream and pastes
Commercial tablets are available for preparation of this solution
•
Calcium hydroxide
•
It is called Limewater, contain not less than 140 mg of Ca(OH)2 in each
100 mL of solution
Cool purified water is the solvent
The solution is intended to be saturated with solute
The solution should be stored in well-filled tightly stopered containers and
kept in a cool place to maintain an adequate conc., of dissolved solute.
The solution is astringent and is employed in dermatological solutions and
lotions
•
•
•
•
•
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
Hydrogen peroxide

It contains 2.5-3% w/v hydrogen peroxide H2O2, suitable preservative may
be added (0.05%)
Is a clear, colorless liquid.
It deteriorates upon long standing also by the effect of light and heat
The solution should be preserved in tight, light-resistant containers, at
temp. not exceeding 35 C
It is categorized as a local anti-infective for use topically on the skin or
mucous membranes.
Its germicidal activity is based on the release of nascent oxygen on contact
with the tissues and its ability to cleanse wounds





Synonym: Peroxide
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
Povidone iodine


Commercial product: Betadine Solution
It is a chemical complex of iodine with PVP
It contains approx. 10% available iodine and slowly released when applied
to the skin
It is employed as surgical scrub and nonirritating antiseptic solution

Thimerosal topical

Is a water-soluble organic mercurial antibacterial agent used topically for
its bacteriostatic and mild fungistatic properties
It is used to disinfect skin and as an application to wounds and abrasions
It has been also applied to the eye, nose, throat in dilution 1:5000
It is also used as a preservative for various preparations
The solution is affected by light and must be maintained in light resistant
containers

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Iodine Tincture
It is a reddish-brown colour tincture
It is prepared from 2% iodine crystal and 2.4% sodium iodide in a vehicle
alcohol/water (44-50% alcohol)
It is a popular local anti-infective agent applied to the skin in general
household first aid
Compound Benzoin tincture
It is prepared from 10% benzoin and lesser amounts of aloe, storax and tolu
balsam
The mixture is macerated in alcohol
It is used to protect and toughen skin in the treatment of bedsores, ulcers,
cracked nipples, and fissures of the anus
Also used in treatment of venereal warts
It is also used as an inhalent for bronchitis and other respiratory conditions
It is best stored in tight, light-resistant containers
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10
0
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
Thimerosal Tincture
The vehicle is water, acetone and 50% alcohol
It must be manufactured and stored in glass or suitably resistant containers
Ethylenediamine is used as stabilizer in the official solution and tincture
The commercial preparation is colored orange red, the colour defines the
area of application
It is a commonly used household antiseptic for application to the skin
abrasions and cuts and in preparation of patients for surgery
Green Soap tincture
65% of active constituent in alcohol
Also contains 2% lavender oil as perfume
Used as detergent
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1
Vaginal douches
• Solution for irrigation cleansing of the vagina, used for hygienic effect
 Solutions
may be prepared from powders or liquid
concentrates.
 The resultant solution contains the appropriate amount of
chemical agents in proper strength
 Boric
acid – astringents - antimicrobial – quaternary
ammonium compound – detergents – oxidizing agents – salts
– aromatics
 Evacuation Enemas
 Rectal enemas are used to cleanse the bowel.
 The enema solution are solutions of; sodium phosphate,
sodium biphosphate, glycerin, docusate sodium, light mineral
oil
 The product will work within 5-10 min
 They are available in disposable plastic squeeze bottles
102

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2
Simple Enema
Take of:
Soft Soap – 1 oz.
Warm water, up to – 1 pint.
Dissolve and mix. For use in constipation. To be
given at body temperature.
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3





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

Also known as otic products, these are simple solutions of drugs in water,
glycerol, propylene glycol or alcohol/water mixture for local use
Hydrogen peroxide (5-volume), Phenol (6% w/w) ear drops
Ear drops are a form of medicine used to treat or prevent ear infections,
especially infections of the outer ear and ear canal (Otitis externa).
Bacterial infections are sometimes treated with antibiotics. Examples are:Gentisone HCL ear drops (containing Gentamicin and hydrocortisone).
Ciproxin HCL ear drops (containing ciprofloxacin and hydrocortisone).
Kenacomb ear drops, containing triamcinolone acetonide, neomycin and
gramicidin (antibiotics) and nystatin (antifungal).
Over the counter ear drops are also available, including spirit drops
(alcohol solution), which dries out the ear, and drops such as Aqua Ear
(used for swimmer's ear) containing a mixture of substances such as
alcohol and acetic acid, to dry the ear and make it difficult for microbes to
grow.
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10
4




Eye drops are sterile aqueous or oily solutions or suspensions
intended for instillation into the eye.
Depending on the condition being treated, they may contain
steroids (e.g. mydriatics, dexamethasone), antihistamines,
sterile
sympathomimetics,
beta
receptor
blockers,
parasympathomimetics (e.g. pilocarpine), parasympatholytics
(e.g. tropicamide or atropine), prostaglandins, non-steroidal
anti-inflammatory drugs (NSAIDs) or topical anesthetics.
Eye drops sometimes do not have medications in them and are
only lubricating and tear-replacing solutions,
and they can also contain anti-redness and similar chemicals.
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5






These are formulated as small-volume solutions is an aqueous
vehicle for instillation into the nostrils
Formulation are isotonic with nasal secretions using sodium
chloride.
Viscosity can be modified using cellulose derivatives
Nasal administration can be used to deliver drugs for either
local or systemic effect.
Locally acting drugs are for example decongestants and
allergy treatments.
Examples of systemically active drugs available as nasal
sprays are migraine drugs, nicotine replacement and hormone
treatments, anti-convulsant.
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6




Are sterile, large volume aqueous–based
solutions for the cleansing of body cavities
(peritoneal dialysis solution) and cleansing
wounds.
They should be made isotonic with tissue
fluid
They are not for oral or parenteral use
For external use only
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7
Spray
An aqueous or oleaginous solutions in the form of
coarse droplets or as finely divided solids to be
applied topically, most usually to the nasopharyngeal
tract or to the skin by means of an atomizer
The type of atomizer used depends on the viscosity
of the spray solution
Drugs used for relief of asthma are commonly
dispensed as spray
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8

Oromucosal preparations: are designed for application to the throat or
oral cavity and can includes solids and semi-solids as well as solutions

Mouthwashes and gargles

These aqueous solutions are for the prevention and treatment of mouth and
throat infections and can contain antiseptics, analgesics and / or astringents
They are intended to bring the medication into contact with mucous surface
of the throat
They are usually diluted with warm water before use
Gargles may have some analgesic effect and provide symptomatic relief
Mouthwash are intended to wash out the mouth , they may be of value for
local hygiene of the mouth




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10
9
Alkaline Gargle and Mouth Wash
Take of:
Bicarbonate
of Soda
1 oz.
Boric Acid
1 oz
Chloride of Sodium
2 oz.
Directions- Add a teaspoonful to 8 ounces of warm
water and use as a gargle, mouth wash or nasal
douche.
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0
Compound Potassium Chlorate Gargle
Take of:
Potassium Chlorate – 6 gr.
Borax
– 3 gr.
Tincture of Myrrh – 5 min.
Water, up to
– 1 oz.
Useful in stomatitis
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1


Gingival and sublingual preparations
These are in the form of drops or sprays for application to
specific areas of the oral mucosa such as the gums for the
prevention and treatment of periodontal disease or under the
tongue to enable fast absorption of active agents into systemic
circulation
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2

Liniments
Are liquid preparation for external use only and may be applied with or
without friction.
They should not be applied to unbroken skin
They are alcoholic or oleaginous solutions or emulsions of various
medicinal substances
For oleaginous liniments, the solvent may be a fixed or volatile oil
(almond, sesame, peanut, wintergreen, turpentine oil)
Alcoholic or hydroalcoholic vehicle are useful when rubefacient or
counterirritant action is desired
 For relief of pain, they may be applied on warmed flannel or lint or may
be painted with a soft brush
 Liniment may be alcoholic solutions
 They should be dispensed in colored bottle
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Menthol Camphor Compound Liniment
 Menthol
– 2 gr.
 Camphor
– 5 gr.
 Oil of Turpentine
– 2 dr.
 Soft Soap- 2 dr.
 Olive Oil, up to
– 1 oz.
 Useful in chronic inflammation of joints.
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Aconite Belladonna and Camphor Liniment (ABC Liniment)
Take of:
Liniment Aconite
Liniment of Belladonna
Each equal parts.
Liniment of Camphor
For use in Rheumatism, etc.
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
Paints
Liquids for application to the skin or mucous membranes in small amounts
using a small brush
The solvent is water, alcohol, ether or acetone
Glycerol is often added to ensure prolonged contact with the skin (viscocity
modifier)

Collodions
Is a clear viscous liquid prepared by dissolving pyroxylin in a 3:1 mixture of
ether and alcohol or acetone/alcohol
Pyroxylin obtained by the action of a mixture of nitric and sulfuric acids on
cotton, consists of cellulose tetranitrate
The resulting solution is highly volatile and flammable
The product is capable of forming a protective film on application to the skin
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Castor oil may be applied to collodion to render the film flexible, permitting
its comfortable use
After evaporation of the solvent leaves a tough , flexible film hold the drug in
intimate contact with the skin

Salicylic acid Collodion

It is 10% solution of salicylic acid in flexible collodion
Has keratolytic effect especially in the removal of corns from the toes
The product is applied as one drop on the corn or wart, allowing time to
dry
As salicylic acid is irritant to normal skin, it should be applied directly on
the corn or wart
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