Effect of Concomitant Administration of Trospium Chloride Extended Release on the Steady-State Pharmacokinetics of Metformin in Healthy Adults

BACKGROUND Overactive bladder (OAB) is often associated with a number of co-morbid medical conditions, including diabetes mellitus. This may necessitate several concomitant treatments, thus creating the potential for drug-drug interactions (DDIs). Trospium is renally eliminated, not metabolized via cytochrome P450; therefore, cytochrome P450 DDIs are unlikely. However, coadministration with another renally eliminated drug (e.g., metformin) may theoretically result in a DDI. OBJECTIVE The objective of this study was to evaluate the pharmacokinetics (plasma and urine) and safety/tolerability of the coadministration of trospium chloride extended release (XR) and metformin under steady-state conditions in healthy male and female subjects. METHODS In a single-centre, randomized, open-label, two-group, two-period study in healthy males and females aged 18-45 years, 44 subjects received oral metformin 500 mg twice daily for 3.5 days during one period, and oral trospium chloride XR 60 mg once daily for 10 days, followed by trospium chloride XR 60 mg once daily for 4 days plus metformin 500 mg twice daily for 3.5 days during the other period. The two periods occurred in a crossover fashion, separated by a 3-day washout period. RESULTS Trospium chloride XR coadministration did not alter metformin steady-state pharmacokinetics. Metformin coadministration reduced trospium steady-state maximum plasma concentration (by 34 %) and area under the concentration-time curve from 0-24 hours (by 29 %). Neither drug's renal clearance was affected. No safety/tolerability issues of concern were observed with coadministration. CONCLUSION No dosage adjustment is necessary for metformin when coadministered with trospium chloride XR.