Bioavailability of digoxin capsules and tablets: effect of coadministered fluid volume

The effect of different coadministered fluid (water) volumes on the consistency of digoxin absorption was studied in 16 male volunteers. Each volunteer received four single-dose treatments (two 0.25-mg digoxin tablets with 30- and 240-mL of water and two 0.2-mg digoxin capsules with 30- and 240-mL of water). Digoxin present in serum and urine samples collected for 48 h after dosing was quantified by RIA. Treatments were compared by evaluating the following model-independent pharmacokinetic parameters: maximum serum concentration (Cmax); time of maximum serum concentration (tmax); area under the serum concentration-time curve for 0-12 h (AUC0-12); cumulative urinary excretion for 0-48 h (CUE48). No significant differences were found between dosage form (tablets versus capsules) and coadministered water volume (30 mL versus 240 mL) for any of the parameters. For both fluid volumes the AUC0-12 and Cmax were significantly larger (p less than 0.01) and the tmax significantly shorter (p less than 0.01) for the capsules than for the tablets. The volume of coadministered water had no effect on the amount of digoxin absorbed from either dosage form.