PROPRANOLOL REDUCES BUPIVACAINE CLEARANCE

Propranolol reduces the clearance of lidocaine by both reducing hepatic blood flow and inhibiting lidocaine metabolism. The authors investigated the possibility that propranolol reduces the clearance of bupivacaine as well. Bupivacaine, 30-50 mg, was administered intravenously to six normal human volunteers, over 10-15 min on two occasions, at least 2 weeks apart. Propranolol, 40 mg orally every 6 h, was used on one occasion, beginning 24 h prior to the bupivacaine administration. The sequence of the sessions was randomized. Twenty-two venous blood samples were obtained over 36 h in order to determine bupivacaine clearance, terminal elimination rate constant, and volume of distribution. All subjects experienced mild CNS toxicity, consisting of tinnitus, facial tingling, or subtle visual disturbances, associated with peak venous plasma concentrations of 0.81 to 2.7 μg/ml. Mean bupivacaine clearance was 0.33 ± 0.12 l/min for the control session and 0.21 ± 0.12 l/min during propranolol use, a significant 35% reduction (P < 0.01). The terminal elimination rate constant (beta) was 0.27 ± 0.16 h-1 for the control session and 0.14 ± 0.069 h-1 with propranolol (P < 0.05); terminal elimination half-lives were 2.6 and 4.9 h, respectively. Volume of distribution was unchanged. Because bupivacaine clearance should be relatively insensitive to hepatic perfusion, it appeared that propranolol caused a substantial inhibition of bupivacaine metabolism at the level of the hepatocyte. These data suggest that concomitant use of propranolol could result in the accumulation of a toxic concentration of bupivacaine.