Summary
Inhibition of platelet function by aspirin results from irreversible inhibition of
platelet cyclooxygenase (COX)-1. While sufficient inhibition is obtained at antiplatelet
doses (75–325 mg/day) in most (≥95%) treated patients, the antiplatelet effect of
aspirin and subsequent cardiovascular risk reduction is much less in clinical settings
and disease-dependent. Several reasons for this “high on treatment platelet reactivity”
are known. This paper reviews the evidence for an interaction between aspirin and
other COX inhibitors, namely non-steroidal antiinflammatory drugs (NSAIDs). Numerous
experimental studies demonstrated a pharmacodynamic interaction between aspirin and
NSAIDs. This likely occurs within the hydrophobic substrate channel of platelet COX-1
and might be explained by molecular competition between inhibitor drugs and substrate
(arachidonic acid) at overlapping binding sites. This interaction is found with some
compounds, notably ibuprofen and dipyrone (metamizole), but not with others, such
as diclofenac and acetaminophen (paracetamol). Hence, this interaction is not a class
effect of NSAIDs and/or non-steroidal analgesics but rather due to specific structural
requirements which still remain to be defined. In vivo studies on healthy subjects and patients tend to confirm this type of interaction
as well as large differences between NSAIDs and non-steroidal analgesics, respectively.
These interactions may be clinically relevant and may increase the cardiovascular
risk in long-term treatment for primary and secondary cardiovascular prevention in
patients with chronic inflammation, such as rheumatoid arthritis. These patients have
an elevated risk for myocardial infarctions and may require chronic antiplatelet treatment
by aspirin in addition to treatment of inflammatory pain.
Keywords
Aspirin - drug-interaction - non-steroidal anti-inflammatory drugs - dipyrone - platelet
function