EFFECT OF ASPIRIN ON HEMOSTASIS: SYNERGISM OR ANTAGONISM WITH NON STEROIDAL ANTI-INFLAMMATORY AGENTS

Aspirin and the other non steroidal anti-inflammatory drugs (NSAIDs) are among the most often prescribed medicines. Co-administration of aspirin and NSAIDs is also common especially among patients suffering from arthritis and cardiovascular disease. An interaction between aspirin and NSAIDs could affect both the antiplatelet effect of aspirin and the safety of these agents in case of co-administration. For example, co-administration of aspirin with another NSAID could produce a pharmacodynamic interaction with subsequent enhancement or inhibition of antiplatelet effect of aspirin. On the other hand, such a pharmacodynamic interaction could result in increased incidence of gastrointestinal and non gastrointestinal haemorrhage. This review aimed to summarize available data on the possible pharmacodynamic interaction between aspirin and NSAIDs and the clinical consequences of such an interaction. Databases were searched electronically for relevant trials. Identified data were quite limited. Theoretically at the molecular level, a competitive interaction between aspirin and NSAIDs could be anticipated in case of prior administration of a NSAID. However, in vitro data indicate that concurrent administration of aspirin and diclofenac potentiates the inhibition of platelet aggregation. Yet, in vivo studies have failed to prove competitive interaction between aspirin and diclofenac in platelet aggregation, or suggest minimal effect of diclofenac on platelet aggregation, when administered concurrently with aspirin. Retrospective studies based on prescription databases have suggested that ibuprofen counteracts the antiplatelet effect of aspirin. There is limited evidence on how NSAIDs affect platelet aggregation in vivo when they are given together with aspirin according to a regular clinical schedule e.g. a morning dose of aspirin and repeated doses of NSAIDs during the day. Existing data suggest an interaction between aspirin and NSAIDs on haemostasis. However, there is controversy regarding the direction of this interaction, i..e. synergism or antagonism. Since, co-administration of aspirin and NSAIDs is quite common in people with comorbidities, further research is needed to clarify the clinical significance of this interaction.