Arterial antithrombotic effects of aspirin, heparin, enoxaparin and clopidogrel alone, or in combination, in the rat.
BACKGROUND
Many antithrombotic drugs may have a deleterious effect on normal haemostasis leading to bleeding complications. The aim of this study was to determine if sub-therapeutic (low) doses of antithrombotic agents, when administered in combination, have enhanced efficacy without augmentation of bleeding time.


METHODS
The antithrombotic effects of i.v. aspirin (4-30 mg/kg), heparin (100-500 U/kg), enoxaparin (4-30 mg/kg) and clopidogrel (10-20 mg/kg) were studied in a rat Folts-like preparation of carotid arterial thrombosis. The frequency of cyclic flow reductions (CFRs; indicating occlusive thrombus formation) and bleeding time were measured. Drug doses that were singly ineffective at preventing occlusive thrombus formation were tested in the following combinations: aspirin (10 mg/kg) with heparin (250 U/kg); aspirin (4 mg/kg) with enoxaparin (4 mg/kg); and aspirin (10 mg/kg) with clopidogrel (10 mg/kg).


RESULTS
Control period (pretreatment) CFRs were not significantly different between groups; average 7.0+/-0.3 CFRs/30 min (n=64). Tail bleeding time before drug(s) was 3.1+/-0.1 min (n=86). When administered alone, aspirin (4-30 mg/kg), heparin (250 U/kg) or enoxaparin (4 mg/kg) had no effect on CFRs or bleeding time. Heparin (500 U/kg), enoxaparin (10 and 30 mg/kg) and clopidogrel (20 mg/kg) significantly decreased CFRs. Single administration of heparin (500 U/kg) or enoxaparin (30 mg/kg) increased bleeding time by 4- or 11-fold. When co-administered, aspirin 10 mg/kg and heparin 250 U/kg decreased CFRs, but also increased bleeding time by 11-fold. However, combination of aspirin and enoxaparin (4 mg/kg each), or aspirin and clopidogrel (10 mg/kg each), decreased CFRs with no effect on bleeding.


CONCLUSIONS
In a preparation of arterial thrombosis in the rat, combinations of sub-efficacious (low) doses of aspirin with enoxaparin or clopidogrel inhibited thrombus formation without augmenting bleeding time. However, low-dose aspirin combined with heparin, whilst inhibiting thrombus formation, exacerbated bleeding time. If these findings translate into the clinic, the use of effective low-dose combinations may have therapeutic advantages.
Daykin
Heather J
HJ
Cardiovascular Therapeutics Unit, Department of Pharmacology, University of Melbourne, Victoria 3010, Australia.
Sturgeon
Sharelle A
SA
Jones
Catherine
C
Wright
Christine E
CE
D000818:Animals; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D001241:Aspirin / Q000008:administration & dosage* / Q000009:adverse effects; D001760:Bleeding Time; D002339:Carotid Arteries / Q000473:pathology; D000077144:Clopidogrel; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D017984:Enoxaparin / Q000008:administration & dosage* / Q000009:adverse effects; D006493:Heparin / Q000008:administration & dosage* / Q000009:adverse effects; D008297:Male; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D013927:Thrombosis / Q000188:drug therapy* / Q000517:prevention & control; D013988:Ticlopidine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives*
D000925:Anticoagulants; D017984:Enoxaparin; D006493:Heparin; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin