BACKGROUND

Topiramate is approved for epilepsy and migraine headache management and has potential antidiabetic activity. Because topiramate and antidiabetic drugs may be co-administered, the potential drug-drug interactions between topiramate and glyburide (glibenclamide), a commonly used sulfonylurea antidiabetic agent, was evaluated at steady state in patients with type 2 diabetes mellitus (T2DM).

METHODS

This was a single-center, open-label, phase I, drug interaction study of topiramate (150 mg/day) and glyburide (5 mg/day alone and concomitantly) in patients with T2DM. The study consisted of 14-day screening, 48-day open-label treatment, and a 7-day follow-up phase. Serial blood and urine were obtained and analyzed by liquid chromatography coupled mass spectrometry/mass spectrometry for topiramate, glyburide, and its active metabolites M1 (4-trans-hydroxy-glyburide) and M2 (3-cis-hydroxy-glyburide) concentrations. Pharmacokinetic parameters were estimated by model-independent methods. Changes in fasting plasma glucose from baseline and safety parameters were monitored throughout the study.

RESULTS

Of 28 enrolled patients, 24 completed the study. Co-administration of topiramate resulted in a significant (p < 0.05) decrease in the glyburide area under the concentration-time curve (25 %) and maximum plasma concentration (22 %), and reduction in systemic exposure of M1 (13 %) and M2 (15 %). Renal clearance of M1 (13 %) and M2 (12 %) increased during treatment with topiramate. Steady-state pharmacokinetics of topiramate were unaffected by co-administration of glyburide. Co-administration of topiramate and glyburide was generally tolerable in patients with T2DM.

CONCLUSION

Glyburide did not affect the pharmacokinetics of topiramate. Co-administration of topiramate decreased systemic exposure of glyburide and its active metabolites; combined treatment may require dosing adjustments of glyburide as per clinical judgment and glycemic control.