Absolute bioavailability of amiodarone in normal subjects

The relative and absolute bioavailability of different oral forms of amiodarone was examined in 12 subjects. The doses were 5 mg/kg iv, two 200-mg commercial tablets by mouth, two 200-mg tablets (new formulation) by mouth, and 400 mg in a drinkable solution. Plasma levels of amiodarone and its N-desethylated metabolite were determined by HPLC. Statistical analysis indicated bioequivalence of the oral forms for all the kinetic parameters examined. After oral dosing, amiodarone was slowly absorbed and the maximum plasma level (0.55 +/- 0.20 mg/l) was reached in 4.5 hr. The absolute bioavailability of oral amiodarone was calculated by comparison of AUCs after oral dosing with those after intravenous injection. A mean oral bioavailability of 65% +/- 22% was indicated. Since the tablets were bioequivalent to the drinkable solution, incomplete absorption seems not be a result of the dissolution characteristics of the commercial formulation but rather of a first-pass effect.