Pharmaceutical technology and extemporaneous compounding of dosage forms
What the exam tests
This domain tests compounding calculations, dosage-form technology, prescription legality, hygiene, stability, and labeling. It covers solutions, powders, suspensions, ointments, suppositories, and drops, with attention to mass-volume concentration and incompatibilities.
Core rules
- A compounding prescription must be legally valid: prescriber details, patient details, date, dosage form, ingredients and quantities, and signature or stamp as required.
- Calculations must be checked independently, especially for potent substances, children’s doses, and alcohol dilutions.
- Percentage solutions are usually mass-volume for solids in liquids: 1% means 1 g in 100 mL.
- Isotonicity, pH, solubility, and compatibility determine whether a preparation is pharmaceutically acceptable.
- Label with the preparation name, strength, quantity, batch or preparation date, expiry, storage conditions, and warning labels.
Worked example
Prepare 100 mL of 0.9% sodium chloride solution from a 10% concentrated stock solution.
Reasoning: 0.9% means 0.9 g NaCl in 100 mL. A 10% stock contains 10 g in 100 mL, so each 1 mL contains 0.1 g. To obtain 0.9 g, measure 9 mL of the 10% stock and add purified water to a final volume of 100 mL. Do not add 91 mL water first and then adjust blindly; measure to volume after mixing. Check clarity, labeling, and expiry.
Traps that cost marks
- Confusing w/v, w/w, and v/v percentages.
- Forgetting that “to 100 mL” means final volume, not added volume.
- Using tap water or an unclean vessel for a preparation intended for mucous membranes or wounds.
- Ignoring incompatibilities such as alkaloids with tannins or oxidizing agents with reducing agents.
- Omitting the beyond-use date and storage instructions.
Exam focus
Show the calculation, state the final volume, and name the quality check.