Pharmacology and Pharmacy Calculations
This domain tests drug classes, routes, storage, controlled-drug handling, and accurate dose calculations, including dilutions and constant-rate infusions.
Calculation rules
Convert all units before calculating: 1 g = 1,000 mg; 1 mg = 1,000 mcg; 1 L = 1,000 mL. Use the formula dose × weight = amount, then amount ÷ concentration = volume. For a 5% solution, 5 g per 100 mL equals 50 mg/mL.
Worked example
An 8 kg cat is ordered 2 mg/kg of a 10 mg/mL solution. Reasoning: 8 kg × 2 mg/kg = 16 mg; 16 mg ÷ 10 mg/mL = 1.6 mL. The answer is 1.6 mL, not 16 mL. Check that the concentration is per mL, not per vial.
Constant-rate infusions
For a CRI, calculate the total dose per hour, then divide by concentration. If a 10 kg dog needs 1 mg/kg/hr from a 1 mg/mL solution, that is 10 mg/hr = 10 mL/hr. Account for the fluid rate and any added drug volume.
Drug classes and safety
Know opioid, alpha-2 agonist, benzodiazepine, NSAID, corticosteroid, antibiotic, antiparasitic, and anesthetic induction classes. Store controlled substances securely and log each use. Check expiry, species contraindications, and route.
Traps
Mixing mg and mcg; placing a decimal in the wrong position; using the vial concentration as the dose; failing to label a mixed solution; ignoring species-specific toxicity, such as permethrin in cats; dispensing without a valid veterinarian-client-patient relationship.