ibuprofen and aspirin

Pharmacodynamic interaction. Aspirin irreversibly acetylates cyclooxygenase-1 (COX-1) in platelets, inhibiting thromboxane A2 production and platelet aggregation. Ibuprofen reversibly binds to the COX-1 active site, and if present at the time of aspirin exposure, it prevents aspirin from accessing the site. This reduces the antiplatelet effect of aspirin. Additionally, both drugs have additive gastrointestinal irritant and ulcerogenic effects, increasing the risk of bleeding.

Reduced cardioprotective effect of aspirin when ibuprofen is taken before or around the same time, potentially increasing the risk of cardiovascular events in patients using aspirin for secondary prevention. The risk of gastrointestinal bleeding and peptic ulceration is also increased due to additive COX-1 inhibition. Renal function may be further impaired in susceptible individuals.

Avoid concomitant use where possible. If an NSAID is required, consider alternatives such as paracetamol or a non-NSAID analgesic. If combined use is necessary, administer aspirin at least 30 minutes before ibuprofen or at least 8 hours after the last ibuprofen dose, to allow aspirin to irreversibly inhibit platelet COX-1 first. Monitor for signs of gastrointestinal bleeding and renal impairment. The evidence for the specific timing recommendation is moderate, and local formulary or specialist guidance should be consulted.

Well-established interaction based on pharmacodynamic studies and clinical observations. The interference of ibuprofen with aspirin's antiplatelet effect has been demonstrated in vitro and in clinical pharmacokinetic/pharmacodynamic studies, though clinical outcome data are mixed. Guidance on timing varies by region and is not universally adopted.