Pharmacology Basics and Medication Safety
Pharmacology Basics and Medication Safety tests routes, simple pharmacokinetics, dosage calculation and the checking habits that prevent medication errors.
Core rules
- Pharmacokinetics is absorption, distribution, metabolism (mainly liver) and excretion (mainly kidney). Half-life is the time for plasma concentration to halve; it sets the dosing interval.
- Routes: oral, sublingual, rectal, topical, inhalation, subcutaneous, intramuscular, intravenous. Intravenous acts fastest; oral is slowest and affected by food and first-pass metabolism.
- Rights of administration: right patient, right drug, right dose, right route, right time, right documentation, plus right to refuse and right reason.
- Common abbreviations: OD once daily, BD twice, TDS three times, QID four times, HS at bedtime, SOS when needed, PRN as required, AC before food, PC after food, NPO nothing by mouth.
- High-alert drugs (insulin, heparin, potassium chloride, digoxin, opioids) need independent double-checking and clear labelling. Watch look-alike, sound-alike names.
- Never crush enteric-coated or sustained-release tablets unless advised; never write U for units or a trailing zero such as 10.0 mg.
Worked example
A 12 kg child needs paracetamol at 15 mg/kg per dose. Dose = 12 × 15 = 180 mg. The syrup available is 120 mg per 5 mL, so volume = (180 ÷ 120) × 5 = 7.5 mL. Reasoning: convert the prescribed weight-based dose to milligrams first, then use the strength on the label to get millilitres; mg and mL are not interchangeable, so the final answer is 7.5 mL, not 180 mL.
Traps that cost marks
- Confusing milligrams with millilitres.
- Crushing a sustained-release tablet to make it easier to swallow.
- Using U instead of writing units.
- Recording a dose before it is actually given.