Overall pharmacokinetics during prolonged treatment of healthy volunteers with digoxin and beta-methyldigoxin

Abstract

Five healthy volunteers received digoxin 0.4 mg or beta-methyldigoxin 0.4 mg i.v., daily for 14 days, in a randomized cross-over arrangement. By monitoring minimal plasma concentrations during multiple dosing, it was found that the steady state pharmacokinetics of digoxin and beta-methyldigoxin could be estimated even better by a one-compartment than by a two-compartment model. The following mean parameters were calculated: the half life of digoxin of 1.54 +/- 0.31 days was significantly shorter than the half life of 2.29 +/- 0.34 days for beta-methyldigoxin. The distribution volume of 807 +/- 187 liters for digoxin was not significantly larger than the 735 +/- 227 liters for beta-methyldigoxin. Renal digoxin clearance of 191 +/- 25 ml/min was significantly higher than both the renal clearance of beta-methyldigoxin of 111 +/- 23 ml/min and also the creatinine clearance, which indicates tubular secretion of digoxin. There was a 2.8-fold accumulation of beta-methyldigoxin injected once a day, which was significantly higher than the 1.80-fold accumulation of digoxin.