Dipyridamole kinetics

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Abstract
The kinetics of the antiplatelet drug dipyridamole were studied in 6 normal subjects (3 men and 3 women) 22-34 yr old. Each received 20 mg i.v. and 4 also took a 50-mg oral dose. Blood samples were collected after each dose for a period of 3 days, and concentrations of dipyridamole were measured by a sensitive and specific high-performance liquid chromatographic assay. Concentrations after the i.v. dose showed a triexponential decline and a terminal half-life of 11.6 .+-. 2.2 h. Total plasma clearance was 8.27 .+-. 1.82 l/h and the apparent distribution volume was 141 .+-. 51 l. Concentrations rose 6-10 h after i.v. dipyridamole in each female subject, but not in the male subjects. Dipyridamole blood/plasma concentration ratio changed from an average of 0.7 over the 1st h to 1.2 after 5 h after the i.v. dose. There was an absorption lag time ranging from 34-75 min after the oral dose; concentrations peaked at .apprx. 2-2.5 h after the dose. The percentage of unbound drug in plasma was 0.88 .+-. 0.24%. Systemic availability of the oral dose was 43 .+-. 13%. These results suggest widely varying concentrations in patients receiving the drug and raise questions about the current clinical practice of using empirical dosage schedules.