Prediction of time-dependent interaction of aspirin with ibuprofen using a pharmacokinetic/pharmacodynamic model.

WHAT IS KNOWN AND OBJECTIVE: Low-dose aspirin is widely used for prevention of thrombosis, but combined use of aspirin with non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, reduces the antiplatelet effect of aspirin. However, there has been no report describing the effects of the timing of the ibuprofen dose on the degree of interaction between low-dose aspirin and ibuprofen. The purpose of this study was to predict the time-course of the antiplatelet effect of low-dose aspirin when ibuprofen is administered as a single dose or repeatedly in combination with aspirin at various time intervals. METHODS: We simulated ex vivo platelet aggregation using a previously developed pharmacokinetic (PK)/pharmacodynamic (PD) model. RESULTS AND DISCUSSION: The antiplatelet effect of low-dose aspirin (81 mg) was predicted to be markedly reduced when ibuprofen (200 mg; the usual prescribed dose in Japan) was administered 1 h or less after aspirin, but not when it was administered more than 2 h after the administration of aspirin. Moreover, the administration of ibuprofen up to 12 h before aspirin completely abrogated the antiplatelet effect of aspirin. When ibuprofen (200 mg) was administered three times daily for 3 days (day 1 to day 3) on a background of continuous low-dose aspirin (81 mg) once daily, 2 h after aspirin, no reduction in the antiplatelet effect of aspirin was predicted on day 1, but a reduction is predicted from day 2, with no return to the initial level until more than 3 days after discontinuation of ibuprofen. A marked reduction in the antiplatelet effect of aspirin was also seen on the same schedule when the dosage of ibuprofen was 150 mg, which is the dose used in over-the-counter (OTC) preparations. WHAT IS NEW AND CONCLUSION: This study indicates that the antiplatelet effect of low-dose aspirin can be markedly reduced with combined use of ibuprofen, depending on the timing of co-administration. As even the lower OTC dose of ibuprofen (150 mg) was enough to affect the antiplatelet effect of aspirin, health professionals should take into account patients' use of OTC ibuprofen when prescribing low-dose aspirin.