No abstract

No abstract

The effects of pretreatment with cimetidine (1 gm daily for 3 days) on the disposition of lidocaine were examined in 18 healthy subjects, seven of whom were chronic cigarette smokers. Each subject received separate oral (200 mg) and intravenous (75 or 100 mg) doses of lidocaine before and after cimetidine. After cimetidine, lidocaine apparent oral clearance (Clo) reduced 42% +/- 7%; oral bioavailability increased 35% +/- 10%; and systemic clearance (Cls) and volume of distribution at steady-state (Vdss) decreased 21% +/- 6% and 20% +/- 7%. Elimination t 1/2 was unchanged. Calculated values for Cls after cimetidine based on reduction in Clo and consequent decrease in hepatic extraction ratio correlated significantly with observed values for Cls (r = 0.67). Women had larger Vdss (64% +/- 19%), longer t 1/2 (50% +/- 18%), and greater oral lidocaine bioavailability (63% +/- 29%) than did men. There was no sex difference in and no influence of cigarette smoking on the effects of cimetidine. The results indicate that cimetidine reduces metabolic clearance of lidocaine. The consequent reduced hepatic extraction explains the observed reduction in Cls.

No abstract

1 The effects of separate 5 day pretreatments of propranolol 120 mg day-1 and 720 mg day-1 on theophylline clearance and metabolism at steady-state were determined in seven healthy males. 2 Propranolol 120 mg day-1 decreased theophylline plasma clearance (CL) by 30%. Clearance of theophylline to each metabolite was reduced by this treatment, clearances to the two demethylated products by 42-43% and clearance to the 8-hydroxylation product by 27%.3 Propranolol 720 mg day-' decreased theophylline CL by 52%. Again, clearance of theophylline to each metabolite was reduced by this treatment, clearances to the two demethylation products by 73-77% and clearance to the 8-hydroxylation product by 44%. 4 These data are consistent with a dose-dependent and selective inhibitory effect of propranolol on the separate forms of cytochrome P-450 involved in theophylline demethylation and 8-hydroxylation.Keywords drug metabolism drug interactions cytochrome P-450 propranolol theophylline