Bioavailability of digoxin tablets in healthy volunteers

The bioavailability of digoxin generic tablets manufactured in Korea (formulations A & B) were compared to a standard (formulation C; Lanoxin brand digoxin, Burroughs Wellcome, USA) in 12 healthy Korean male volunteers (mean age 31.4 years) in a single dose, randomized, complete block crossover study. Using a Latin square design, each of the subjects was randomized to the order number and allocated to each of the three treatments of 0.5 mg oral digoxin. Digoxin concentrations in serum and urine samples collected for 48 hours after dosing were measured by fluorescence polarization immunoassay and radioimmunoassay, respectively. Treatments were compared by using nonlinear least squares regression analysis to evaluate the following pharmacokinetic parameters: maximum serum concentration (Cmax); time of maximum serum concentration (Tmax); area under the serum concentration-time curve for 0-12 hours (AUC0-12); and cummulative urinary excretion for 0-48 hours (CUE0-48). Mean AUC0-12, Cmax, and CUE0-48 values for formulations B and C were significantly different from formulation A (p < 0.001), but not significantly different from each other. Based on AUC0-12 and CUE0-48, respectively, the relative availability of formulation B was 87.5% and 89.6% and the relative availability of formulation A was 43% and 35% when compared to formulation C (the standard).