Effect of rifampin and tobacco smoking on the pharmacokinetics of ropivacaine.

OBJECTIVE

Our objective was to assess the effect of rifampin (INN, rifampicin) and tobacco smoking on the pharmacokinetics of ropivacaine.

METHODS

A randomized, 2-phase, crossover study was performed in both a group of 10 healthy nonsmokers and a group of 8 healthy smokers. In both groups each subject ingested daily for 5 days either placebo or 600 mg rifampin. On day 6 each subject received intravenously over 30 minutes a single dose of 0.6 mg/kg ropivacaine. Ropivacaine, 3-hydroxyropivacaine (3-OH-ropivacaine), and (S) -2',6'-pipecoloxylidide (PPX) in venous plasma and urine were measured for up to 12 hours and 24 hours, respectively. Pharmacokinetic parameters were calculated with noncompartmental methods, and t tests were used for comparisons between the phases and between the smokers and nonsmokers. The electrocardiogram was monitored for 3 hours.

RESULTS

There were no statistically significant differences in the area under the plasma concentration-time curve (AUC), plasma clearance (CL), or half-life (t(1/2)) of ropivacaine between the smokers and nonsmokers. However, smokers excreted in urine 31% more 3-OH-ropivacaine and 62% less PPX than nonsmokers did. Rifampin decreased the AUC of ropivacaine in nonsmokers by 52% and in smokers by 38%. In nonsmokers rifampin increased the CL of ropivacaine by 93% and shortened its t(1/2) by 25%. In smokers rifampin increased the CL of ropivacaine by 47% and shortened its t(1/2) by 20%. Rifampin decreased the urinary excretion of 3-OH-ropivacaine in nonsmokers by 74% and in smokers by 68%, and it increased the excretion of PPX by 97% and 158%, respectively. No clinically significant differences in the QTc times were found between the groups or treatments.

CONCLUSIONS

Tobacco smoking increases the excretion of 3-OH-ropivacaine in urine, probably because of the increased cytochrome P450 (CYP) 1A2-mediated metabolism of ropivacaine, and decreases the excretion of CYP3A4-formed PPX in urine. Rifampin considerably increases the metabolism of ropivacaine to PPX and decreases the metabolism to 3-OH-ropivacaine in both nonsmokers and smokers.