Medication Reconstitution
Many drugs used in sterile products, especially antibiotics, come in a dry powder
form. It is extremely important that the correct diluent be selected and the appropriate
calculations be performed to ensure correct concentrations and stability of the finished
product.
Antibiotics in powder form generally have an extended shelf life; however, once
diluted most antibiotics lose their potency after a relatively short period of time.
Pharmacy technicians often reconstitute many of these drugs. Having a good
understanding of how to reconstitute powders will aid you in preparing these drugs for
patient use.
Definitions
Diluent is a clinically inactive ingredient/liquid used to dilute or reconstitute a
medication. It is also used to convert a dry form of a substance to a liquid form. When
reconstituting medications, read the directions to find out which diluent needs to be
used. Water or normal saline (NS) solution is often used to dilute medicines and to
liquefy dry, powdered forms of medicines. Diluents are typically inserted with a
syringe through the rubber stopper of the medication vial for injectable drugs. For Oral
or topical suspension, the diluent is measured properly, added to the medication
container and shaken really well to ensure the powders are dissolved properly.
Dilution is the extent to which the concentration of a mixture is reduced.
Dilution ratio is a special ratio indicating the number of parts of an active ingredient to
the number of parts of inactive ingredients in a solution. For example, a 1:4 dilution
ratio means that, out of 5 total parts, 1 part is active and 4 parts are inactive. Adding 4
parts water to 1 part powdered medication would provide a dilution ratio of 1:4.
Reconstitution is a process of combining the dry form of a mixture with a fluid to
achieve a usable state. It is also the process of diluting liquid concentrate to achieve a
usable state.
Suspension is a liquid in which fine particles are dispersed throughout a fluid, where
they are supported by the buoyancy of shaking or stirring. If a suspension is left
standing, the solid particles settle. Antibiotics are often supplied as oral suspensions.
Unstable means that the pharmaceutical formula is easily broken down to a state of
diminished effectiveness. Breakdown can occur rapidly with reconstituted solutions.
Foods, solutions, and certain medications that are unstable, such as reconstituted
medications, have a short shelf life. They must be discarded if they are not used in a
timely manner.
Sterile Container – the contents of the medication container is free of biologic
contaminants (example: bacterial or viral).
Diluent Identification
Some medications are very unstable in liquid form. Therefore, they are supplied
in a dry form to which an inactive diluent is added just before use. The information
about the specific type and amount of diluent to be added to achieve specific
concentrations is provided on the product label. Selecting the correct diluents (liquid or
solution) is important in reconstituting a medication. Incorrect diluents used can affect
the medication’s stability, efficacy and safety. Use of the incorrect diluent may result in
loss of potency of the medication, an unwanted chemical interaction, or a shorter period
of stability of the reconstituted medication. The information regarding the correct
diluent to be used is clearly written on the product label. To ensure that the ingredients
are compatible or incompatible with the diluent, the pharmacist or pharmacy technician
should check the reference books available in the pharmacy or may consult the product
information leaflet.
Common Diluents for injectable drugs
Normal saline is a term commonly used interchangeably with 0.9% sodium chloride
(NaCl) injection and is the concentration of sodium chloride within the human blood
stream. For reconstituting powder for oral suspension, Sterile water is commonly used
as diluent to dissolve the powder.
Standard Name
Dextrose 5% in Water
Lactated Ringers
Normal Saline
Sterile Water for Injection
Bacteriostatic Water
Alternate Name
Common Abbreviation
5% Dextrose Injection
D5W
Ringers Lactate
LR
0.9% Sodium Chloride Injection
NS
SWFI
BW
Measuring device / equipment used to measure diluents/liquids for reconstitution
1.
Graduated Cylinder
2.
Calibrated Medication cup
3.
Syringe
4.
Beaker
Reconstituting Medications
1. Interpreting Prescription Orders and Reading Labels for Reconstituted
Medications
Sample A. Examine the directions on the following label for an oral suspension to be
reconstituted:
Rx:
Amoxicillin 200mg/5ml suspension
The order includes the form, oral suspension, but does not mention that the drug
requires reconstitution or describe how to prepare it. The pharmacist or pharmacy
technician must read the medication label and / or product information to determine
how to prepare the medication.

Reading Labels Directions on the label state the precise amount and type of
liquid diluent to add in order to achieve specific dilutions or concentrations of
the drug per milliliter.

The directions always state conditions and time limits for storage after
reconstitution to liquid form.

Some products must be discarded immediately, while others may be refrigerated
for several hours to several days so that they can be used for additional doses.
Examine and interpret the medication label:
1.
The route is oral. This is important to note because there are injectable antibiotics
and other drugs with similar names made specifically for intramuscular or intravenous
routes. Diluents for oral preparation do not necessarily need to be sterile whereas the
sterility of the diluent is very important for injectable medications.
2.
The type of diluent is water. Most oral suspension diluents use tap water unless
otherwise specified. Pediatric patients and immunocompromised patients may need
Sterile water to ensure bacterial content of the diluent is avoided.
3.
The total amount of diluent to be added is 57 mL, can be added in two parts: 30 mL
for the first mix and add the remaining 27 mL for the second in order to avoid lumping
of the suspension.
4.
After reconstitution, the drug concentration will yield 200 mg/ 5 mL water. The
total amount of medication is 75 mL, although only 57 mL of water was
added. This discrepancy is due to displacement of liquid by the powder. Both
ingredients occupy space.
5.
Discard after 14 days. Refrigeration after reconstitution is preferable to ensure
stability of the medication. It is important to educate the patient on the storage
condition once the powder is reconstituted.
Sample B. Read and interpret the prescription label and indicate the required
information below (checklist):
1. Form and route of medication: Oral Suspension
2. Type of diluent to be used: Water
3. Amount of diluent to add to bottle: 47.6 ml
4. Mixing directions: Add 47.6ml of water gradually and shake well.
5. Unit dose concentration after reconstitution: 25mg per 5 ml
6. Total volume in container after reconstitution: 60ml
7. Number of unit doses in container after reconstitution: 12 unit doses of 5 mls
8. Storage location and condition in dry form: room temperature at 30°C
9. Storage location after reconstituted: room temperature
10. Expiration, or discard, time after reconstitution: 14 days
11. Additional instruction to patient: Shake well before using
Sample C. Calculating, reconstituting and measuring doses and interpreting the
prescription order
Rx order: Erythromycin susp. 300mg tid x 7 days
1. Form and route of administration: Oral Suspension
2. Amount and type of diluent to be added: 77 mls of water
4. Mixing directions: Add 77mls of water gradually and shake well.
5. Unit dose concentration after reconstitution: 200 mg per 5 ml
6. Total volume in container after reconstitution: 100 ml
7. Storage location and condition in dry form: room temperature at 30°C
9. Storage location and condition after reconstituted: refrigerate, do not freeze
10. Expiration, or discard, time after reconstitution: 10 days
11. Additional instruction to patient: Shake well before using; medication may be
taken with or without food
Prescription interpretation:
Rx: Erythromycin 300mg tid x 7 days
Interpretation: Take 300mg three times a day for seven days.
Calculation: Once reconstituted, the suspension will yield 200mg per 5 mls. The
prescription order requires the patient to take 300mg per dose. Calculate the equivalent
volume in mls of the reconstituted suspension to yield 300mg per dose.
1.
Use ratio and proportion:
200mg : 5ml:: 300mg: X
X = 300mg x 5 ml
200mg
X = 7.5 ml per dose equivalent of 300mg Erythromycin
2.
Calculate the amount of medication needed to be dispensed:
= 7.5 mls (amount per dose) x 3 (three times a day-frequency of administration) x 7
days (duration of treatment)
Answer: 157.5 mls
3.
Round up the quantity. The bottle will yield 100 mls of reconstituted
suspension, since we cannot break the bottle, 2 x 100mls Erythromycin 200mg/5ml
suspension will be dispensed to the patient to be consumed for the treatment duration
indicated (7 days). Special instruction to “discard the remainder” of the suspension
should be given to the patient during patient counseling.
4.
Prescription Labeling:
Dawood Khan National Military Hospital
Pharmacy Department
Dr. Omar Abdullah
Date: 20 April 2013
Patient: Ali Karimi
Father: Abdul Karimi
Medication: Erythromycin 200mg/5ml susp Quantity:
200 mls
Directions: Take 7.5 mls (300mg) three times daily for 7 days.
*Keep in the refrigerator. Discard the remainder
*May be taken with or without food
*Shake well before using
Reconstituting Injectable Medications
Before you can produce a reconstituted product, you need to read the package
insert or drug label to identify the proper diluent when reconstituting a powder for IM
or IV injection. Diluents are used to prepare powdered medications for transfer to IV
solutions. Not all diluents are suitable to reconstitute injectable medications.
Calculate amounts of reconstituted solutions:
1. Use the provided resources, especially the label and package insert.
2. Double check units in all calculations.
3. Ensure your answers make sense by working the problem in reverse or solving for a
different factor.
Determine the correct diluent:
1. Always use your reference materials.
2. Determine if you need bacteriostatic or sterile agents.
3. Ensure the information on a diluent label or product label matches what is in the
reference material.