Interaction of low molecular weight heparin with ketorolac

Postoperative patients may receive ketorolac, a nonsteroidal antiinflammatory drug that inhibits platelet function, for analgesia and may receive low-molecular-weight heparin (LMWH) for thrombosis prevention. We investigated whether the combination of these two agents increases blood loss in a rabbit model of hemostasis. In a randomized, blinded study, animals received either intramuscular ketorolac (0.5 mg/kg or 1.0 mg/kg) and subcutaneous saline solution, subcutaneous LMWH (100 U/kg) and intramuscular saline solution, ketorolac (0.5 mg/kg or 1.0 mg/kg) and subcutaneous LMWH (100 U/kg), or intramuscular and subcutaneous saline solution given 30 minutes before ear incision and measurement of blood loss. Collagen-induced platelet aggregation was examined and anti-Xa levels were determined by using a chromogenic substrate method. As compared with results in saline- treated controls, blood loss was significantly increased in animals receiving ketorolac in a dose of 1.0 mg/kg but not in those treated with 0.5 mg/kg. The addition of LMWH did not further increase blood loss above that observed with either dose of ketorolac alone. Platelet aggregation was inhibited by both doses of ketorolac. The anti-Xa levels in the LMWH- treated animals were comparable to those measured in patients receiving these agents for prophylaxis (0.09 to 0.13 U/ml). We conclude that in the rabbit model, LMWH does not augment ketorolac-associated bleeding when both agents are used in doses comparable to those given to human patients.