A comparison of every-third-day versus daily low-dose aspirin therapy on serum thromboxane concentrations in healthy men and women

Aspirin's antithrombotic effect is mediated predominately by inhibition of platelet cyclooxygenase-1, leading to a decline in serum thromboxane A(2) c oncentrations. We performed a placebo-controlled, randomized, double-blind trial to determine whether aspirin could be given at 3-day intervals and st ill achieve potent serum thromboxane inhibition. One hundred nine healthy m en and women with no recent exposure to aspirin and no contraindications to its use participated. Subjects received 325 mg, 81 mg, or 40 mg of plain a spirin every third day, with placebo on other days; 81 mg of aspirin every day; or placebo every day. Serum concentrations of thromboxane B-2 (the met abolite of thromboxane A(2)) were measured at 3-day intervals during a 31-d ay treatment period, as well as 4, 7, and 14 days after treatment ended. Se rum thromboxane B-2 concentrations were nearly identical during treatment w ith 325 mg of aspirin every third day or 81 mg of aspirin per day (86% inhi bition [84%, 89%] and 85% inhibition [73%, 96%], respectively). An aspirin dose of 81 mg every third day was nearly as potent (74% inhibition [70%, 79 %]), whereas 40 mg of aspirin every third day achieved only 50% inhibition (40%, 60%). Every-third-day low-dose aspirin regimens (325 and 81 mg) deser ve comparison with daily low-dose aspirin regimens in controlled clinical t rials because the former regimens could prove to have equal efficacy with r educed toxicity.