The absolute and relative bioavailability of dipyridamole from different preparations and the in vitro-in vivo comparison.

The in vitro liberation and the bioavailability (BV) of dipyridamole (D) in three different brands (A, B, C) were determined in a three way cross-over study on 12 healthy subjects. Also, the pharmacokinetics of D given intravenously was investigated. The in vitro liberation of B is only to be achieved by repeated touching. The tmax for the preparations, expressed as mean +/- s mean amounts as follows: A: 0.8 +/- 0.06; B: 1.1 +/- 0.1; C: 0.8 +/- 0.09 hours and is in the case of B significantly different (p less than 0.05) from the others. The cmax values (A: 1.01 +/- 0.25; B: 1.16 +/- 0.15; C: 1.51 +/- 0.3 mumol X l-1) and the AUC values (A: 3.8 +/- 0.9; B: 3.1 +/- 0.5; C: 3.8 +/- 0.7 mumol X h X l-1) are not different. The absolute BV of D is 27 +/- 5.5% (range: 11-44%) independent of the used brand. In 4 subjects a second tmax at the 4th-6th hour is to be observed irrespective of the way of dosing. An enterohepatic circulation is assumed. It is concluded that the determination of the in vitro liberation is a necessary and useful parameter, but cannot be used alone for characterization of the BV in every case, as e.g., for problem drugs.