Population pharmacokinetics of digoxin in Japanese patients - A 2-compartment pharmacokinetic model

Objective: To clarify the observed variability of digoxin disposition by pe rforming population pharmacokinetic analysis in a Japanese population. Design: Retrospective analysis of clinical pharmacokinetic data. Patients and participants: Data were obtained from 106 patients with heart failure and atrial fibrillation (43 males and 63 females). Methods: Digoxin concentrations in serum were measured by fluorescence pola risation immunoassay. Population pharmacokinetic analysis was performed usi ng a 2-compartment open pharmacokinetic model with the computer program NON MEM. Results: 246 serum concentrations were obtained. Final pharmacokinetic. par ameters were: CL (L/h) = (0.036 . TBW + 0.112 . CLCR) . 0.77(SPI) . 0.784(C CB), V-1 = 1.83 L/kg, V-2 = 22.6 L/kg and Q = 0.629 L/h/kg, where CL is tot al body clearance, VI and V2 are the apparent volumes of distribution in th e central and peripheral compartments, Q is intercompartmental clearance, T BW is total bodyweight (in kg), CLCR is creatinine clearance (in ml/min), S PI = 1 for concomitant administration. of spironolactone (and zero otherwis e) and CCB = 1 for concomitant administration of calcium antagonists (and z ero otherwise). Concomitant administration of digoxin and spironolactone re sulted in a 23% decrease in digoxin clearance. Concomitant administration o f digoxin and calcium antagonists (diltiazem, nicardipine, nifedipine or ve rapamil) resulted in a 21.6% decrease in digoxin clearance. Conclusions: The estimated population parameter values may assist clinician s in the individualisation of digoxin dosage regimens.