Pharmacology · single question
What is the MECHANISM OF ACTION of propranolol increasing lidocaine toxicity?
Show answer and explanation
Correct answer: B. Beta-blockers decrease cardiac output → reduced hepatic blood flow → decreased lidocaine clearance, AND compete for the same hepatic CYP enzymes
✓ B) Two mechanisms: reduced cardiac output → less hepatic clearance + CYP enzyme competition.
Propranolol (non-selective beta-blocker) increases AMIDE LA (lidocaine) toxicity by: (1) Propranolol decreases cardiac output → decreased hepatic blood flow → SLOWER lidocaine metabolism in liver → higher plasma levels; (2) Propranolol and lidocaine COMPETE for same CYP enzymes (CYP1A2, CYP2D6) in the liver → less lidocaine metabolism → prolonged duration + toxicity. CLINICAL IMPORTANCE: in patients on propranolol, limit LA dose, aspirate carefully, inject slowly. The same interaction applies to other amide LAs (mepivacaine, bupivacaine).
Propranolol (non-selective beta-blocker) increases AMIDE LA (lidocaine) toxicity by: (1) Propranolol decreases cardiac output → decreased hepatic blood flow → SLOWER lidocaine metabolism in liver → higher plasma levels; (2) Propranolol and lidocaine COMPETE for same CYP enzymes (CYP1A2, CYP2D6) in the liver → less lidocaine metabolism → prolonged duration + toxicity. CLINICAL IMPORTANCE: in patients on propranolol, limit LA dose, aspirate carefully, inject slowly. The same interaction applies to other amide LAs (mepivacaine, bupivacaine).