The effect of oral cimetidine on total and unbound serum lidocaine concentrations in patients with suspected myocardial infarction

In this study, we prospectively evaluated the effect of oral cimetidine on serum lidocaine concentrations in 6 patients with suspected myocardial infraction. Compared to baseline lidocaine levels, total lidocaine concentrations increased by 8.2 ± 7.8% at 6 hours, 16.4 ± 9.0% at 12 hours and 27.9 ± 9.4% at 24 hours after two doses of oral cimetidine. Unbound lidocaine concentrations increased by 14.3 ± 4.1% at 6 hours, and 18.3 ± 10.3% at 24 hours after cimetidine. In patients with myocardial infraction (3), total lidocaine concentrations increased by 24.2 ± 10.4%, whereas unbound lidocaine increased by 8.9 ± 10.2% at 24 hours. Therefore, increases in total lidocaine concentrations after cimetidine administration were considerably less than those previously reported and empiric dosage reductions of lidocaine in patients receiving cimetidine may not be appropriate.