Pharmaceutical Dosage Forms and Compounding
Core concepts
Know the major dosage forms - tablets, capsules, liquids (solutions, suspensions, emulsions), topical preparations (creams, ointments, gels), suppositories, inhalers, injectables, and transdermal systems - and how each is prepared, stored, and administered. Understand the difference between a solution (clear, dissolved) and a suspension (particles that settle and must be shaken), and why that matters for dosing accuracy. Learn the basics of compounding: equipment, weighing and measuring, geometric dilution for mixing powders, levigation, and the importance of a clean, organized workspace and accurate records.
Traps in questions
Questions often test the reason a form is chosen (for example, why a suspension must be shaken, or why an enteric coating exists) rather than the definition. Watch for confusion between sterile and non-sterile compounding, and between terms like ointment (greasy, occlusive) and cream (water-containing, less greasy). Another trap is assuming all liquids are interchangeable; a suspension dosed without shaking delivers an inaccurate dose.
Rule of thumb
Match the dosage form to the route and the patient's needs, and remember that preparation method affects dose accuracy. For powders, use geometric dilution to ensure uniform mixing of a small amount of active ingredient into a larger bulk.
Worked example
When compounding a small quantity of a potent powder into a larger base, add the powder to an approximately equal volume of base, mix thoroughly, then add successive equal portions of base until the full amount is incorporated - this is geometric dilution and prevents uneven distribution.