Possible drug–drug interaction between quetiapine and lamotrigine – evidence from a Swedish TDM database

Abstract

AIM The aim of the present study was to investigate a previously proposed interaction between quetiapine and lamotrigine resulting in reduced serum quetiapine concentrations. METHODS Data on 402 patients subjected to analysis of quetiapine concentration in serum were extracted from a routine therapeutic drug monitoring database. Among these patients, those concomitantly treated with lamotrigine (n = 22) were identified and matched with 22 controls receiving quetiapine while unexposed to lamotrigine. The dose-corrected quetiapine concentrations (C : D ratios) in the two groups were compared in both paired and unpaired analyses. RESULTS Patients co-treated with lamotrigine had a lower mean C : D ratio (0.71, 95% CI 0.46, 0.97) compared with controls (1.64, 95% CI 1.00, 2.28). Dose-corrected quetiapine concentrations were 58% lower in patients co-medicated with lamotrigine. CONCLUSIONS This study indicates that lamotrigine exposure is associated with substantially reduced serum concentrations of quetiapine, possibly due to induced glucuronidation. These findings need to be confirmed in experimental studies.