Pharmaceutics, Dosage Forms and Drug Delivery
Core concepts
This domain asks you to select and justify dosage forms. Know the advantages and limits of tablets, capsules, syrups, suspensions, emulsions, suppositories, injections, inhalers, transdermal patches, and modified-release systems. Understand the difference between immediate-, delayed-, extended-, and controlled-release mechanisms (matrix, reservoir, osmotic, ion-exchange). Know routes of administration and first-pass effects: oral drugs undergo hepatic metabolism before systemic circulation, while sublingual, rectal (partially), transdermal, and parenteral routes avoid it. Understand particle size effects on deposition in the lung, and the role of theophylline-like therapeutic windows in choosing controlled release. Paediatric and geriatric considerations (taste, swallowing, dosing flexibility) frequently appear.
Traps in questions
- Assuming all modified-release products can be crushed or split; many cannot.
- Forgetting that rectal absorption is partial and variable due to venous drainage.
- Confusing a suspension (solid in liquid) with an emulsion (two immiscible liquids).
- Overlooking that transdermal delivery is limited by skin permeability and drug molecular size.
Worked example / rule of thumb
A patient cannot swallow tablets and needs a drug available only as an extended-release matrix tablet. The correct reasoning is: do not crush; look for an alternative formulation or route rather than altering the product. Rule of thumb: "if the label says ER, SR, XL, or CR, assume it must stay intact unless the product information explicitly permits splitting."