Absorption of digoxin from different oral preparations in normal subjects during steady state.

Abstract

Digoxin bioavailability was studied in 6 normal volunteers during chronic dosing. The absorption of digoxin was estimated by: (1) steady‐state serum dtgoxin levels; (2) the area IInder the serllm concentration‐time curve (AUC) du ring a dosittg interval; and (3) the excretion of digoxin in the urine during one dosing interval during steady state. Using the mean of these three methods, the absolute bioavailability of the 0.25 mg digoxin tablet (Lanoxin) was 62%, and an equivalent dose of digoxin solution was 77%. When the dose of digoxin administered was doubled (0.125 mg to 0.25 mg), the steady state serum level increased by 50% for oral administration and 80% for intravenous administration. Despite failure to double serum level and AUC, there was doubling in urinm‐y digoxin excretion. Results indicate that urinary excretion of digoxin is the most valid measure of bioavailability of oral digoxin preparations.