Pharmacy and Pharmacology
This domain tests whether you can move safely between a prescription on the treatment sheet and a syringe in your hand: drug classes and their monitoring, dosage forms, storage and handling rules, and the arithmetic that links a dose written in mg/kg to a volume drawn in mL.
Core rules
- Every dose is a chain: body weight, then dose rate, then total amount, then concentration, then volume. Convert pounds first (1 kg = 2.2 lb).
- Percent solutions are grams per 100 mL, so 1% = 10 mg/mL, 2% = 20 mg/mL, and 0.9% saline = 9 mg/mL.
- Ratio expressions: 1:1000 epinephrine is 1 g in 1000 mL, which is 1 mg/mL, not 0.1 mg/mL.
- Constant rate infusions: (mg/kg/hr x kg x hours) / concentration = amount to add to the bag; subtract the drug volume from the diluent.
- Extra-label use is legal under AMDUCA only inside a valid veterinarian-client-patient relationship, when no labeled alternative exists for the condition, with extended withdrawal times in food animals.
- Storage: insulin refrigerated and never frozen, reconstituted vaccines used within the labeled window, light-sensitive drugs protected, controlled substances double-counted in a locked log.
- Chemotherapy and hormone products need closed-system transfer and personal protective equipment.
Worked example
A 15 kg dog is prescribed 8 mg/kg of a 4% oral suspension every 12 hours. Total dose = 15 x 8 = 120 mg. Because 4% = 40 mg/mL, the volume is 120 / 40 = 3 mL per dose. A 100 mL bottle therefore holds about 33 doses, roughly 16 days of therapy, which is exactly the kind of calculation that flags a refill problem before the client runs out.
Traps that cost marks
Mixing mg/kg with mg/lb; decimal slips between mg and mcg (0.2 mg/kg = 200 mcg/kg); assuming dose ceilings do not exist (bupivacaine about 2 mg/kg, lidocaine about 4 mg/kg without epinephrine); and drawing from a bottle whose concentration changed after a manufacturer reformulation.