The relationship between the plasma concentration of bepridil and its efficacy in the treatment of atrial fibrillation in Japanese patients.

Bepridil hydrochloride is used for treatment of atrial fibrillation (AF) in Japan. We investigated the relationship between plasma concentrations of bepridil just before dosing (Cbep) and its clinical efficacy in Japanese patients (n=36) with AF. Patients were treated orally with 100, 150 or 200 mg/d bepridil. Cbep were measured with UV-HPLC. In the first 14 d, when 150, 200, 250 or 300 ng/mL was set as a boundary value, the efficacy of bepridil was significantly higher in all patients with Cbep above than below the boundary value (p<0.05). In the maintenance stage (3 months longer after starting therapy), the efficacy of bepridil was significantly higher in patients with Cbep above than below 300 ng/mL (p=0.04). The clinical efficacy of bepridil was closely related to Cbep. The target value of Cbep to obtain a clinical benefit was approximately 300 ng/mL. Monitoring Cbep should be useful in the treatment of patients with AF.