Biopharmaceutics & Pharmacokinetics
Prof. Sayed I. Abdel-Rahman Boudy
Lecture 1
General Introduction & Definitions
Course Description
• This course will introduce you to the basic concepts and principles in
biopharmaceutics and pharmacokinetics.
• Biopharmaceutics describes the role of dosage form in the absorption of
drugs in the body.
• Pharmacokinetics describes the processes involved in the Absorption of a
drug (in part determined by biopharmaceutics) from its site of
administration into the blood circulation, Distribution of the drug to its
sites of action, Metabolism of the drug, and subsequent Excretion of the
drug from the body (ADME).
• Processes that influence the pharmacokinetics of drugs, including
formulation, physico-chemical and physiological factors will be discussed.
The use of mathematical equations to describe the pharmacokinetic
concepts are introduced.
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Course Goals and Objective
Course Goals:
The goals of this course is to provide the student with:
1. An understanding of the fundamental concepts of
biopharmaceutics and pharmacokinetics in humans
2. Knowledge about the application of biopharmaceutics in drug product
evaluation (Bioavailability and Bioequivalence)
3. The Course is considered as a prerequisite for Clinical Pharmacokinetics
which concerns the application of pharmacokinetics in disease state for
dosage regimen design and therapeutic drug monitoring
Couse objective
You will gain an understanding of bioavailability and bioequivalence of drug
products and the principles of the ADME processes of a drug in the body
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General Introduction & Definitions(1)
Pharmaceutics
The science which deals with the formulation of drugs and the in vitro
performance of the dosage forms.
Biopharmaceutics
Biopharmaceutics is the study of the factors influencing the
bioavailability of a drug in man and animals and the use of this
information to optimize pharmacological and therapeutic activity of
drug products’’.
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General Introduction & Definitions (2)
Another definition is; it is the study of physicochemical properties of
drugs & dosage forms and effects of routes of administration on the
rate and extent of drug absorption.
Examples of some factors include:
1. Chemical nature of a drug (e.g., weak acid or weak base)
2. Inert excipients used in the formulation of a dosage form (e.g.
diluents, binding agents, disintegrating agents, coloring agents, etc.)
3. Method of manufacture (dry granulation and/or wet granulation)
physicochemical properties of drugs (pKa, particle size and size
distribution, partition coefficient, polymorphism, etc.).
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General Introduction & Definitions (3)
Generally, the goal of biopharmaceutical studies is to
develop a dosage form that will provide consistent
bioavailability at a desirable rate. The importance of a
consistent bioavailability can be very well appreciated if
a drug has a narrow therapeutic range (e.g. digoxin)
where small variations in blood concentrations may
result in toxic or sub-therapeutic concentrations.
Pharmacokinetics
(in Greek: “pharmacon” meaning drug and “kinetikos”
meaning putting in motion, sometimes abbreviated as
“PK”). It is the kinetic study of ADME (Absorption,
Distribution, Metabolism and Elimination) of the drug.
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General Introduction & Definitions (4)
Clinical Pharmacokinetics
The application of pharmacokinetic data to the most effective
and safe therapeutic management to the individual patient.
Pharmacodynamics
It refers to the relationship between the drug concentration at
the site of action (receptors) and the pharmacologic
response), i.e., study of the biologic and therapeutic effects
of the drugs. It is the major concern of pharmacology.
Therefore, drug administration is divided into 2 phases:
a. A pharmacokinetic phase that relates dose, frequency and
route of administration to drug level-time relationship in the
body, and
b. A pharmacodynamic phase that relates the concentration of
the drug at the site(s) of action to the magnitude of the
effect(s) produced.
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General Introduction & Definitions (5)
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General Introduction & Definitions (6)
• Thus, pharmacodynamics explores what a drug does to
the body, whereas pharmacokinetics explores what the
body does to the drug.
• Pharmacokinetics is divided into several areas which
includes the extent and rate of Absorption,
Distribution, Metabolism and Excretion. This is
commonly referred to as the ADME.
• Absorption is the process of a substance entering the
body.
• Distribution is the dispersion or dissemination of
substances throughout the fluids and tissues of the
body.
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General Introduction & Definitions (7)
• Metabolism is the irreversible transformation of
parent compounds into metabolites.
• Excretion is the elimination of the substances
from the body.
• Disposition: Once a drug is in the systemic
circulation (immediately for intravenous
administration and after the absorption step in
extravascular administration),it is distributed
simultaneously to all tissues including the
organs responsible for its elimination.
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General Introduction & Definitions (8)
The distinction between elimination and distribution
is often difficult. When such a distinction is either not
desired or is difficult to obtain, disposition is the term used.
In other words, disposition is defined as all the processes
that occur subsequent to the absorption of the drug.
Hence, by definition, the components of the disposition
phase are distribution and elimination
• Elimination is the irreversible loss of drug from the site
of measurement (blood, serum, plasma). Elimination of
drugs occur by one or both of: metabolism & excretion
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Blood Plasma & blood Serum
• Blood plasma is the liquid component of blood,
in which the blood cells are suspended. It makes
up about 55% of total blood volume. Blood
plasma is prepared simply by spinn12ing a tube
of fresh blood in a centrifuge until the blood cells
fall to the bottom of the tube. The blood plasma
is then decanted.
• blood serum is the clear liquid that separates
from blood when it is allowed to clot completely,
and is therefore blood plasma from which
fibrinogen has been removed during clotting.
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Drug plasma level-time curve (1)
Figure 1. A typical plot (rectilinear paper) of plasma concentration versus time
following the administration of a drug by an extravascular route. MTC,
minimum toxic concentration; MEC, minimum effective concentration.
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Drug plasma level-time curve (2)
• Onset of action It is the time at which the administered
drug reaches the therapeutic range and begins to produce
the effect.
• Duration of action It is the time span from the beginning
of the onset of action up to the termination of action.
• Termination of action Is the time at which the drug
concentration in the plasma falls below the minimum
effective concentration (MEC).
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Drug plasma level-time curve (3)
• Therapeutic range Is the plasma or serum concentration (e.g.
µgml-1) range within which the drug is likely to produce the
therapeutic activity or effect. Table 1.1 provides, as an
example, the therapeutic range of selected drugs.
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Pharmacokinetic Parameters (1)
There are data and parameters
• The data are set experimentally as time
(independent variable on the X access of the
curve) and concentration (dependant variable
on the Y- access)
• The parameters are obtained from the curve.
They are either PK or PD parameters.
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Pharmacokinetic Parameters (2)
PK parameters:
1. Peak plasma concentration, C max:
The maximum plasma conc. Which is related to the
dose, rate of absorption(ka) and rate of elimination (K)
2. Time of peak conc, tmax:
the time taken to reach Cmax
3. Area under the curve. AUC:
This is equal to the total amount of drug absorbed after
administration
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