Local Anesthetic Metabolism - Verified

| Factor | Effect | | :--- | :--- | | | High extraction ratio for lidocaine → reduced hepatic perfusion (e.g., heart failure, cirrhosis) decreases clearance → toxicity risk. | | CYP450 inhibition | Cimetidine, amiodarone, fluconazole (CYP3A4 inhibitors) → ↓ LA clearance. | | CYP450 induction | Rifampin, phenytoin, St. John’s Wort → ↑ LA clearance, potentially reducing duration. | | Liver disease (Cirrhosis) | Reduced CYP activity & flow → dose reduction of amides (e.g., lower bupivacaine dose) is mandatory. | | Age & Neonates | Immature CYP system (neonates) → prolonged half-life (e.g., lidocaine t½ 3 hrs vs 1.5 hrs in adults). |

Once the liver has broken the anesthetic down—stripping it of its anesthetic power and its lipid disguise—the remains are handed to the kidneys. The kidneys act as the final gatekeepers, flushing the inert metabolites into the bladder and out of the body. local anesthetic metabolism