Pharmaceutical Sciences
Pharmaceutical Sciences in the OMSB Pharmacist Exam integrates pharmaceutics, pharmacology, medicinal chemistry, and pharmacognosy. Questions test whether you can connect drug physicochemical properties and receptor mechanisms to measurable pharmacokinetic and clinical outcomes.
Core rules
- For a one-compartment IV drug, t½ = 0.693 × Vd / CL. Clearance determines maintenance rate; Vd determines loading dose.
- Bioavailability F applies to oral loading dose: Loading dose = (Vd × target concentration) / F. Maintenance dose = (CL × target concentration × dosing interval) / F.
- First-order elimination gives constant t½; zero-order (phenytoin at high concentration, ethanol) gives concentration-dependent clearance and saturable metabolism.
- Prodrugs require activation (enalapril to enalaprilat); chiral drugs can differ in activity (S-warfarin is more potent). Polymorphs differ in dissolution, not necessarily intrinsic activity.
- Excipients are not inert: lactose, sulfites, benzyl alcohol, and propylene glycol can cause toxicity or intolerance.
Worked example
A 70 kg patient needs an oral drug with Vd 0.7 L/kg, CL 3.5 L/h, F 0.7, target Css 2 mg/L, dosed every 12 h. Vd = 49 L. Loading dose = (49 × 2) / 0.7 = 140 mg. Maintenance dose = (3.5 × 2 × 12) / 0.7 = 120 mg q12h. Check: the maintenance rate is CL × Css = 7 mg/h; dividing by F adjusts for incomplete absorption.
Traps
- Using Vd as a real body-fluid volume rather than a proportionality constant.
- Forgetting F in oral loading doses, or using renal clearance alone as total clearance.
- Applying a fixed t½ to saturable drugs such as phenytoin.
- Assuming a salt form is equivalent milligram-for-milligram to the base.