Effects of meloxicam on platelet function in healthy adults: a randomized, double-blind, placebo-controlled trial.

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase-1 (COX-1), thereby inhibiting platelet function via blockade of thromboxane A2 (TxA2) formation, and COX-2, the enzyme that mediates inflammatory responses. Meloxicam is a relatively COX-2-selective anti-arthritis drug that shows significant TxA2 inhibition, albeit less than traditional NSAIDs. A randomized, double-blind, placebo-controlled trial was conducted in 79 healthy adults to compare the effects of once-daily therapeutic (7.5 mg, 15 mg) and supratherapeutic (30 mg) doses of meloxicam with extended-release indomethacin (Indo-ER 75 mg once daily) on bleeding time, TxA2 formation, and platelet aggregation. The authors measured platelet aggregation to COX-1-dependent (ADP arachidonate) and COX-1-independent (high-dose collagen) agonists, bleeding time, serum TxB2, and clotting times (aPTT and PT) after 8 days' administration and at 3 and 6 hours after steady-state dosing. Meloxicam significantly decreased TxB2 production compared with placebo in a dose-dependent fashion, reaching a peak of 77% inhibition 6 hours after 30 mg meloxicam; Indo-ER blocked TxB2 formation by 96% at the same time point. However, neither acute nor 8 days' administration of meloxicam at any dose caused a significant increase in bleeding time or inhibition of platelet aggregation to any agonist when compared with placebo. By contrast, Indo-ER significantly increased the bleeding time and inhibited platelet aggregation to COX-1-dependent agonists 6 hours after dosing. Clotting times were unaffected by any drug. It was concluded that unlike nonselective NSAIDs, meloxicam's blockade of TxA2 formation (even at supratherapeutic doses) does not reach levels that result in decreased in vivo platelet function, as measured by bleeding time and aggregometry. In this study of healthy subjects, meloxicam did not interfere with platelet-mediated hemostasis.