Effect of obesity on serum amiodarone concentration in Japanese patients: population pharmacokinetic investigation by multiple trough screen analysis

To evaluate the influence of obesity on pharmacokinetics of amiodarone (AMD) using Non-Linear Mixed Effects Modelling (nonmem) in Japanese patients treated with oral therapy. Serum concentrations of AMD were determined by high performance liquid chromatography. One hundred and fifty-one trough concentrations from 23 patients receiving repetitive oral AMD were collected. Body mass index (BMI) and body fat percentage were measured. Estimates generated using nonmem indicated that the clearance of AMD was influenced by BMI, age and daily dosage of AMD. The final pharmacokinetic model was CL (L/h) = 0.16 . TBW . 0.53(AGE >= 65) . 0.78(BMI >= 25) . DD0.51, V-d (L) = 10.2 . TBW, where CL is total body clearance, TBW is total body weight (kg), DD (mg/kg/day) is daily dosage of AMD, AGE (years) >= 65 = 1 for patient was 65 years old or over and 0 otherwise, BMI (kg/m(2)) >= 25 = 1 for patient was 25 kg/m(2) or over and 0 otherwise and V-d is apparent volume of distribution. The clearance of AMD decreased significantly by 22.3% with a BMI higher than 25 kg/m(2). The clearance of AMD also decreased significantly by 46.9% when patient age was more than 65 years. Population pharmacokinetic analysis confirms that obesity affects the pharmacokinetics of AMD.