Pharmacology and Medication Safety
What this domain tests
This domain tests pharmacokinetics and pharmacodynamics, high-alert medicines, the rights of administration, dose calculation, adverse reactions, interactions and adjustments in renal or hepatic impairment. Expect calculation items and scenarios about preventing harm.
Core rules
- Pharmacokinetics is absorption, distribution, metabolism and excretion. Pharmacodynamics is what the drug does to the body, including agonist and antagonist action.
- The therapeutic index is the ratio between toxic and effective doses; a narrow index demands monitoring, as with digoxin, warfarin, lithium and aminoglycosides.
- High-alert medicines carry a heightened risk of serious harm: insulin, anticoagulants, opioids, concentrated electrolytes, chemotherapy and neuromuscular blockers.
- The rights of administration include right patient, drug, dose, route, time and documentation. They support, but do not replace, clinical judgement and double-checking.
- Calculate doses with consistent units. Convert milligrams to micrograms by multiplying by 1,000; convert micrograms to milligrams by dividing by 1,000.
- Check renal function for renally cleared drugs, liver function for hepatically metabolised drugs, and interactions with food, alcohol and other medicines.
- Report suspected adverse drug reactions through the national pharmacovigilance system.
Worked example
A 24 kg child is prescribed 15 mg/kg/day of an antibiotic divided every 8 hours. Daily dose = 15 × 24 = 360 mg. Three doses per day means 360 ÷ 3 = 120 mg per dose. If the suspension is 50 mg/5 mL, each 5 mL contains 50 mg, so the volume is 120 ÷ 50 × 5 = 12 mL. The reasoning is to calculate the daily dose, divide by the number of doses, then convert milligrams to millilitres using the concentration.
Traps that cost marks
- Confusing milligrams and micrograms, or writing a trailing zero such as 1.0 mg instead of 1 mg.
- Abbreviating units as U; write units in full.
- Crushing modified-release tablets or opening capsules without advice.
- Giving an intravenous push faster than the manufacturer or protocol allows.
- Assuming the five rights make a prescription safe when the dose is outside the therapeutic range.