Pharmacology and Therapeutics
What this domain tests
Rational prescribing, drug classes and their dental applications, interactions, and adverse effects relevant to the mouth.
Core rules
- Local anaesthetics: amide agents (lidocaine, articaine, bupivacaine) are metabolised in the liver; esters (benzocaine) by plasma esterases. The maximum dose of lidocaine with adrenaline is about 7 mg/kg (commonly capped near 500 mg), and 4.4 mg/kg for plain lidocaine. Adrenaline 1:80,000 means 12.5 µg per 1 mL.
- Analgesics: paracetamol is first line; NSAIDs are effective for dental pain but are avoided in peptic ulcer disease, renal impairment, asthma with NSAID sensitivity, and third-trimester pregnancy.
- Antibiotics are adjunctive to drainage and debridement, not a substitute. Amoxicillin is a common first choice; metronidazole covers anaerobes; penicillin allergy warrants clindamycin or a macrolide depending on local guidance.
- Adverse effects: tetracyclines cause intrinsic staining, amoxicillin causes rash and candidosis, NSAIDs cause gastric irritation, and chlorhexidine causes staining and taste disturbance.
- Interactions: warfarin with metronidazole or azoles raises the INR; erythromycin and azoles inhibit CYP3A4.
Worked example
A patient on warfarin needs metronidazole for a dental abscess. Reasoning: metronidazole inhibits warfarin metabolism and raises the INR. The safer approach is to choose an alternative antibiotic, or, if metronidazole is essential, coordinate with the physician for INR monitoring and dose adjustment while maintaining local measures.
Traps
- Prescribing antibiotics for a drained, localised abscess without systemic involvement.
- Quoting local anaesthetic maximum doses per cartridge rather than by weight.
- Forgetting that adrenaline-containing solutions are avoided in uncontrolled hyperthyroidism and phaeochromocytoma.