TY - JOUR T1 - Biomarker Optimization to Track the Antithrombotic and Hemostatic Effects of Clopidogrel in Rats JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 369 LP - 377 DO - 10.1124/jpet.106.119156 VL - 322 IS - 1 AU - William A. Schumacher AU - Jeffrey S. Bostwick AU - Martin L. Ogletree AU - Anne B. Stewart AU - Thomas E. Steinbacher AU - Ji Hua AU - Laura A. Price AU - Pancras C. Wong AU - Robert P. Rehfuss Y1 - 2007/07/01 UR - http://jpet.aspetjournals.org/content/322/1/369.abstract N2 - We determined the dose response of the ADP antagonist clopidogrel (0.3-50 mg/kg p.o.) in rat models of thrombosis and provoked bleeding and correlated these activities to ex vivo platelet activation. Carotid artery thrombosis was induced by FeCl2. Bleeding time was measured by mesenteric vessel puncture and renal cortex or cuticle incision. Platelet biomarkers included standard ADP-induced aggregation, P2Y12 receptor occupancy, and phosphorylation of vasodilator-stimulated phosphoprotein. Clopidogrel decreased thrombus weight up to 78%, caused maximal prolongation of cuticle and mesenteric bleeding, but had little effect on renal bleeds. Due to the steep mesenteric dose response, further comparisons concentrated on cuticle bleeding. The half-maximal inhibitory dose (ED50) for thrombus reduction was 2.4 ± 0.4 mg/kg, with 10 mg/kg providing optimal blood flow preservation and thrombus reduction. The ED50 for bleeding was 10.5 ± 3.4 mg/kg. Increased bleeding was intermediate (3-fold) at 10 mg/kg and maximal (6-fold) at 30 mg/kg. All biomarkers were affected, but with differing sensitivity. ED50s for peak platelet aggregation to 10 μM ADP (11.9 ± 0.4 mg/kg) and the vasodilator-stimulated phosphoprotein index (16.4 ± 1.3 mg/kg) approximated the higher ED50 for bleeding. ED50s for ligand binding (3.0 ± 0.3 mg/kg) and late aggregation (5.1 ± 0.4 mg/kg) better matched the lower ED50 for antithrombotic activity. Aspirin exerted lesser effects on bleeding (42-70% increase in all models) and thrombosis (24% inhibition). In summary, antithrombotic doses of clopidogrel have limited effects on bleeding and standard measures of platelet aggregation. Other biomarkers may be more sensitive for tracking antithrombotic efficacy. The American Society for Pharmacology and Experimental Therapeutics ER -