A NEW METHOD FOR MEASUREMENT OF PLASMA-CONCENTRATION OF ORALLY-ACTIVEGLYCOPROTEIN IIB IIIA ANTAGONISTS/

A bioassay for determining concentrations of antiplatelet compounds in plasma or aqueous solution has been developed. The method uses an ali quot of plasma from treated animals to inhibit collagen-induced platel et aggregation in pooled platelet-rich plasma (PRP) obtained from dono r dogs. The concentration in plasma from treated animals was estimated using a standard curve of inhibition established using plasma from un treated animals which had been spiked with known amounts of compound. For independent validation, plasma concentrations of certain compounds were determined in identical dog plasma samples by both bioassay and HPLC. Results from the two methods were concordant. The bioassay provi des an accurate and sensitive method for measuring antiplatelet activi ty without the need for extraction of plasma samples and may be used t o measure activity in any solution which is compatible with PRP. This assay is routinely used to provide an estimate of absorption of prodru gs and systemic conversion to active compound after oral dosing. Some of the compounds of interest are ester-acid pairs with the inactive es ter prodrug being cleaved to the active acid following administration. Compounds were administered orally (ester) or IV (acid) and blood sam ples were taken periodically for 24 hours. Plasma concentration of act ive moiety was determined for each time point and the area under the c urve (AUC) of concentration vs. time was calculated. Comparing the AUC s for oral and IV routes of administration yielded the Oral Systemic A ctivity (OSA), a measure of active compound available after oral dosin g.