Published online by Cambridge University Press: 15 September 2005
Summary
Background and objective: Recent studies have suggested that cytochrome P-450 isoenzyme 1A2 has an important role in lidocaine biotransformation. We have studied the effect of a cytochrome P-450 1A2 inhibitor, ciprofloxacin, on the pharmacokinetics of lidocaine. Methods: In a randomized, double-blinded, cross-over study, nine healthy volunteers ingested for 2.5 days 500 mg oral ciprofloxacin or placebo twice daily. On day 3, they received a single dose of 1.5 mg kg−1 lidocaine intravenously over 60 min. Plasma concentrations of lidocaine, 3-hydroxylidocaine and monoethylglycinexylidide were determined for 11 h after the start of the lidocaine infusion. Results: Ciprofloxacin increased the mean peak concentration and area under plasma concentration–time curve of lidocaine by 12% (range −6 to +46%; P < 0.05) and 26% (8–59%; P < 0.01), respectively. The mean plasma clearance of lidocaine was decreased by ciprofloxacin by 22% (7–38%; P < 0.01). Ciprofloxacin decreased the area under the plasma concentration–time curve of monoethylglycinexylidide by 21% (P < 0.01) and that of 3-hydroxylidocaine by 14% (P < 0.01). Conclusion: The plasma decay of intravenously administered lidocaine is modestly delayed by concomitantly administered ciprofloxacin. Ciprofloxacin may increase the systemic toxicity of lidocaine.