Food and Drug Administration 

Science Paper 

 9/8/2006

Concomitant Use of Ibuprofen and Aspirin: Potential for Attenuation of the AntiPlatelet Effect of Aspirin 

Healthcare professionals should be aware of an interaction between low dose aspirin (81 

mg per day) and ibuprofen which might render aspirin less effective when used for its 

anti-platelet cardioprotective effect. Healthcare professionals should advise consumers 

and patients regarding the appropriate concomitant use of ibuprofen and aspirin. 

Summary 

• Existing data using platelet function tests suggest there is a pharmacodynamic 

interaction between 400mg ibuprofen and low dose aspirin when they are dosed 

concomitantly. The FDA is unaware of data addressing whether taking less than 

400 mg of ibuprofen interferes with the antiplatelet effect of low dose aspirin. 

• The clinical implication of this interaction may be important because the 

cardioprotective effect of aspirin, when used for secondary prevention of 

myocardial infarction, could be attenuated. 

• For single doses of ibuprofen, the pharmacodynamic interaction can be minimized 

if ibuprofen is given at least 8 hours before or at least 30 minutes after immediate 

release aspirin (81mg; not enteric coated). 

• The clinical implication of the interaction has not been evaluated in clinical 

endpoint studies. 

• There is no clear data regarding the potential effect of chronic ibuprofen dosing of 

greater than 400mg on the antiplatelet effect of aspirin. 

• The timing of dosing of ibuprofen and low-dose aspirin is important for 

preserving the cardioprotective effect of aspirin. 

Recommendations for Concomitant Use 

• Health care providers should counsel patients about the appropriate timing of 

ibuprofen dosing if the patients are also taking aspirin for cardioprotective effects. 

• With occasional use of ibuprofen, there is likely to be minimal risk from any 

attenuation of the antiplatelet effect of low dose aspirin. 

• Patients taking immediate release low-dose aspirin (not enteric coated) and 

ibuprofen 400mg should take the ibuprofen at least 30 minutes after aspirin 

ingestion, or at least 8 hours before aspirin ingestion to avoid any potential 

interaction. 

• Other nonselective OTC NSAIDs should be viewed as having potential to 

interfere with the antiplatelet effect of low-dose aspirin unless proven otherwise. 

• Analgesics that do not interfere with the antiplatelet effect of low dose aspirin 

should be considered for populations at high risk for cardiovascular events. 
• Recommendations about concomitant use of ibuprofen and enteric-coated low 

dose aspirin cannot be made based upon available data. One study showed that 

the antiplatelet effect of enteric-coated low dose aspirin is attenuated when 

ibuprofen 400mg is dosed 2, 7, and 12 hours after aspirin.6

Discussion 

Background 

Ibuprofen has been marketed in the United States as an anti-inflammatory, 

analgesic, and antipyretic drug for decades. It is widely available in a variety of strengths 

and formulations for children and adults as single-ingredient over-the-counter (OTC) and 

prescription products, and can also be found in combination OTC and prescription 

products. 

Chemically, ibuprofen is a propionic acid derivative and a member of the class of 

non-steroidal anti-inflammatory drugs (NSAIDs). The NSAIDs include aspirin, and 

several other classes of organic acids, including the propionic acid derivatives naproxen 

and ketoprofen, acetic acid derivatives diclofenac and indomethacin, and the enolic acid 

piroxicam, and newer agents such as celecoxib. 

How does ibuprofen work and why does it interact with aspirin? 

All NSAIDs work by inhibiting the enzyme cyclooxygenase (COX). Aspirin 

inhibits COX irreversibly, while all non-aspirin NSAIDs are reversible inhibitors of 

COX. There are two forms of cyclooxygenase; namely, COX-1 found in blood vessels, 

stomach and kidney, and COX-2, which is induced in settings of inflammation by 

cytokines and inflammatory mediators. A putative COX-3 has been suggested but not 

proven in humans.1 All currently available OTC NSAIDs are nonselective COX 

inhibitors, and inhibit both COX-1 and COX-2 to varying degrees. The antipyretic, 

analgesic, and antiinflammatory actions of NSAIDs are related to their ability to inhibit 

COX-2. Side effects such as gastrointestinal (GI) bleeding and renal toxicity are a result 

of the inhibition of COX-1 and are well known complications of NSAID therapy2,3,4. By 

inhibiting COX-1, the NSAIDs prevent the formation of thromboxane from arachadonic 

acid, and thereby prevent thromboxane-induced platelet aggregation. Aspirin has an 

irreversible anti-platelet effect, while other NSAIDs, including ibuprofen, have a 

reversible anti-platelet effect.5

 Low dose aspirin is effective in the secondary prevention 

of cardiovascular events because of its antiplatelet effect. Because they bind at similar 

sites on COX, concurrent use of aspirin and ibuprofen may change the pharmacodynamic 

effect of either drug depending on the timing of dosing of each drug. 

What types of aspirin are currently available Over-the-Counter?

 Aspirin is available over-the-counter as a tablet, buffered tablet, effervescent 

tablet, or caplet in immediate-release formulations and as a tablet in enteric-coated 

formulations in strengths ranging from 81 mg to 500 mg. 

 

What is the interaction between aspirin and ibuprofen in single dose studies? 

It has been demonstrated in published and unpublished human ex vivo studies, 

that ibuprofen interferes with the antiplatelet activity of low dose aspirin (81 mg; not 

enteric coated) when they are ingested concurrently.6

 The mechanism by which this 
occurs may be through competitive inhibition of the acetylation site of cyclooxygenase in 

the platelet. Both ibuprofen (reversible inhibition) and aspirin (irreversible inhibition) 

occupy nearby sites on cyclooxygenase, such that the presence of ibuprofen interferes 

with aspirin binding. Once the ibuprofen releases from the binding site, COX will not be 

inhibited because some aspirin available to bind will have been excreted due to aspirin’s 

short half-life. This ibuprofen interference attenuates the expected aspirin-mediated 

irreversible inhibition of thromboxane B2 (TXB2) production and attenuates the expected 

inhibition in platelet aggregation. 

There are no clinical endpoints studies conducted specifically to evaluate the 

interaction. Attenuation of 90% or more of the antiplatelet effect of aspirin has been 

defined as clinically significant7 by some investigators. Unpublished single dose trials 

with ibuprofen 400 mg indicate that interference with aspirin’s antiplatelet activity, as 

measured by TXB2 levels and platelet activation studies, occurs when ibuprofen is taken 

within 30 minutes after immediate release aspirin dosing. The interaction also occurs 

when a single dose of ibuprofen 400 mg is taken within 8 hours prior to aspirin dosing. 

At least 8 hours should elapse after ibuprofen dosing, before giving aspirin, in order to 

avoid significant interference. 

What is the interaction between aspirin and ibuprofen in a multiple dose study? 

One published study demonstrated that if immediate-release aspirin 81 mg is 

given daily for an 8 day run-in, followed by ibuprofen 400 mg dosed at 1, 7, and 13 hours 

after the daily aspirin dose for the next 10 days, then no interference is found with the 

aspirin-induced inhibition of thromboxane, when measured as TXB2 production ex vivo.7 

How can the data regarding the interaction between aspirin and ibuprofen from the 

single and multiple dose studies be interpreted? 

It thus appears that taking low-dose immediate release aspirin at least 30 minutes 

before ibuprofen will preserve the anti-platelet effect of aspirin. 

Does the same interaction occur with enteric- coated aspirin? 

A published study showed that with no aspirin run-in period, enteric-coated 

aspirin 81 mg given daily with ibuprofen 400 mg dosed 2, 7, and 12 hours after aspirin, 

leads to interference with aspirin-induced inhibition of thromboxane, when measured as 

TXB2 production ex vivo.6

 This seems to contradict the observations of other studies 

using non-enteric-coated aspirin but may be explained by the absorption of enteric-coated 

aspirin being delayed compared to non-enteric-coated aspirin. More data are needed to 

reach a conclusion about the interaction between a single daily enteric-coated low dose 

aspirin and multiple daily doses of ibuprofen. 

What is the relationship between these observations and clinical outcomes? 

There has not been a prospective, randomized clinical trial with pre-identified 

cardiovascular endpoints that could provide data to clarify the clinical consequence of 

such concomitant dosing with ibuprofen and low dose aspirin. Epidemiological data on 

the cardiovascular event clinical outcome of concomitant dosing has been 

equivocal.8,9,10,11,12,13,14 
Do other nonprescription pain relievers show a similar interaction with aspirin? 

Acetaminophen appears to not interfere with the antiplatelet effect of low dose 

aspirin. 6

 FDA is unaware of studies that have looked at the same type of interference by 

ketoprofen with low dose aspirin. One study of naproxen and low-dose aspirin has 

suggested naproxen may interfere with aspirin’s anti-platelet activity when they are coadministered.15 However, naproxen 500 mg administered two hours before or after the 

administration of aspirin 100 mg did not interfere with aspirin’s antiplatelet effect. There 

is no data looking at doses of naproxen less than 500mg. Naproxen is available OTC 

only as 220mg. Prescription strengths of naproxen are 250, 375, and 500mg. 

Conclusions 

• There may be a pharmacodynamic interaction between ibuprofen and aspirin 

when they are dosed concomitantly. This interaction may interfere with the 

antiplatelet activity of the aspirin, as measured by TXB2 levels and platelet 

activation. 

• The clinical implication of this interaction is unclear, but may be important since 

the cardioprotective effect of aspirin, when used for secondary prevention of 

myocardial infarction, could be minimized or negated. 

• A negative clinical impact on aspirin’s cardioprotection is unlikely from an 

occasional dose of ibuprofen because the effect of aspirin taken daily is longlasting. 

• Ibuprofen given at least 30 minutes after immediate-release aspirin or at least 8 

hours before taking immediate-release aspirin does not appear to interfere with 

aspirin’s anti-platelet effect. 

References 

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