Pharmacology
This domain tests local anaesthetics, analgesics, antibiotics and emergency drugs, with emphasis on doses, contraindications and interactions. Calculations and patient-specific risk are common.
Local anaesthetics
- Lidocaine 2% with 1:100000 epinephrine is standard. The maximum lidocaine dose is about 4.4 mg/kg, with an absolute limit around 300 mg. A 1.8 mL cartridge of 2% lidocaine contains 36 mg.
- Articaine 4% has a higher maximum dose and good bone penetration; mepivacaine 3% is useful without vasoconstrictor; bupivacaine is long-acting. Always calculate both anaesthetic and vasoconstrictor limits.
Analgesics and antibiotics
- Ibuprofen 400 mg every six to eight hours or paracetamol 1 g every six hours, maximum 4 g daily, are first-line. Avoid aspirin in children and use caution with NSAIDs in renal disease.
- Amoxicillin 500 mg every eight hours is common; amoxicillin-clavulanate, metronidazole and clindamycin are alternatives. Antibiotics are not a substitute for drainage.
Worked example
A 60 kg patient needs lidocaine 2% with 1:100000. Reasoning: 60 x 4.4 mg = 264 mg maximum. Each 1.8 mL cartridge contains 36 mg, so about seven cartridges is the theoretical limit. Clinically, use the lowest effective dose and account for epinephrine.
Traps that cost marks
Do not exceed weight-based doses. Do not give articaine or lidocaine without checking allergy and vasoconstrictor risk. Antibiotic prophylaxis is not routine for every cardiac patient. NSAIDs interact with anticoagulants and can worsen asthma.