FDA advises about potential attenuation of anti-platelet effect of low-dose aspirin with concomitant use of ibuprofen

FDA recently released an information sheet advising healthcare professionals about a potential pharmacodynamic interaction between low-dose aspirin (81 mg/d) and ibuprofen 400 mg when they are dosed concomitantly. This interaction may attenuate aspirin's anti-platelet cardioprotective effect in patients taking aspirin for secondary prevention of myocardial infarction.

Although the clinical implications of the interaction have not been evaluated in clinical end point studies, some unpublished trials involving single-dose ibuprofen 400 mg have demonstrated through measurements of thromboxane B₂ (TXB₂) levels and studies of platelet activation that ibuprofen ingested within 30 minutes of taking immediate-release aspirin may interfere with aspirin's antiplatelet activity. The possible mechanism for the interference may be the competitive inhibition of the acetylation site of cyclooxygenase (COX) in the platelet. Similar interference also has been observed when a single dose of ibuprofen has been taken 8 hours before aspirin or sooner.

Occasional use of ibuprofen by patients likely carries a minimal risk of the interaction, according to FDA, because of aspirin's long-lasting anti-platelet effects when taken daily.

FDA also said that it could not issue recommendations at this time about the effects of chronic ibuprofen doses of <400 mg or >400 mg, nor about the effects of ibuprofen on enteric-coated low-dose aspirin because clear data for those situations are not available.

FDA recommends that other nonselective OTC NSAIDs should be viewed as having potential to interfere with the antiplatelet effect of low-dose aspirin unless proven otherwise. In addition, analgesics such as acetaminophen that do not interfere with the antiplatelet effect of low-dose aspirin should be considered for populations at high risk for cardiovascular events.

SOURCES US Food and Drug Administration. Concomitant use of ibuprofen and aspirin: potential for attenuation of the anti-platelet effect of aspirin. Washington, DC: US Food and Drug Administration; September 8, 2006. Available at: http:// http://www.fda.gov/cder/drug/infopage/ibuprofen/science_paper.htm. Accessed November 1, 2006.

US Food and Drug Administration. New information for healthcare professionals: Concomitant use of ibuprofen and aspirin. Washington, DC: US Food and Drug Administration; September 2006. Available at: http:// http://www.fda.gov/cder/drug/infosheets/hcp/ibuprofen_aspirinhcp.htm. Accessed November 1, 2006.