Effects of paracetamol on the pharmacokinetics of ciprofloxacin in plasma using a microbiological assay

Abstract

Background and objective: Pharmacokinetic drug interactions may result in a decrease or increase in the oral bioavailability of some drugs. Therefore, co-administration of drugs should be avoided, or at least undertaken only when careful therapeutic drug monitoring is possible. Because of the common practice of co-administering paracetamol (acetaminophen) for fever in patients taking the antibacterial ciprofloxacin for infection, we investigated the influence of paracetamol on the pharmacokinetics of ciprofloxacin.

Methods: In a randomised, two-way crossover study, 10 healthy male volunteers received a single oral dose of ciprofloxacin 500 mg or ciprofloxacin 500 mg plus paracetamol 500 mg. Pharmacokinetic parameters were measured in plasma samples using a microbiological assay.

Results: No significant differences were found as a result of concomitant administration of paracetamol in the ciprofloxacin pharmacokinetic parameters oral clearance (CL/F) and apparent volume of distribution (Vd/F). However, the ratio of the area under the concentration-time curves (AUCs) suggested that paracetamol increases ciprofloxacin concentrations on average by 16%. Concomitant administration of paracetamol slightly increased ciprofloxacin AUC(infinity) from 14.37 +/- 0.91 to 16.71 +/- 0.99 microg . h/mL (p = 0.073) and ciprofloxacin maximum plasma concentration (C(max)) from 2.52 +/- 0.18 to 2.61 +/- 0.24 microg/mL (p = 0.113), while slightly decreasing time to ciprofloxacin C(max) from 1.5 to 1.3 hours (p = 0.376).

Conclusion: The results confirm an increased concentration-time profile of ciprofloxacin when the latter is co-administered with paracetamol. We believe that a pharmacokinetic interaction may have occurred.