Variability in Response to Non-steroidal Anti-inflammatory Drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of inflammatory pain. Pain is a highly subjective experience, and selecting an analgesic regimen that provides optimal pain relief for a specific patient can be challenging. Moreover, patients often express a preference for a particular NSAID, raising the possibility that the efficacy in relieving pain is variable among individuals. However this has never been studied systematically. The clinical decision-making process has been further complicated by the recognition that NSAIDs cause serious thrombotic adverse events in some patients (1). Elucidating the factors that influence an individual patient's risk of cardiovascular complications and the likelihood of analgesic efficacy will enable clinicians to prescribe NSAIDs rationally in order to maximize their therapeutic benefit while minimizing the risk of adverse cardiovascular events.

NSAIDs are a chemically diverse class of therapeutic agents that exert their analgesic and anti-inflammatory effects via inhibition of cyclooxygenase (COX)-1 and/or COX-2, enzymes that catalyze the first committed step in prostaglandin (PG) synthesis. PGs produce a diverse array of biologic effects via activation of prostanoid receptors, and play important roles in a variety of pathologic and homeostatic processes (2). COX-2 is readily induced in response to pro-inflammatory stimuli and has been considered the primary source of inflammatory PGs. In contrast, the production of PGs with homeostatic functions, such as gastric epithelium cytoprotection, has been ascribed to COX-1, which is constitutively expressed in most tissues (2). Consequently, COX-2-selective NSAIDs, including rofecoxib, valdecoxib, and celecoxib, were developed in order to retain the anti-inflammatory and analgesic effects of inhibition of COX-2-derived PG formation, while avoiding the gastrointestinal toxicity of traditional NSAIDs (i.e. aspirin, ibuprofen, naproxen, etc) that inhibit both isoforms. Although fewer gastrointestinal complications were observed in clinical trials, treatment with COX-2-selective NSAIDs increased the risk of serious cardiovascular adverse events, including myocardial infarction, stroke, and heart failure (1,3).

The risk of thrombotic events associated with the use of NSAIDs, particularly those selective for COX-2, is mediated via suppression of COX-2-derived prostacyclin formation in endothelial and vascular smooth muscle cells (4,5). Prostacyclin possesses potent anti-thrombotic and vasodilatory effects, and thus acts as a general inhibitor of platelet activation in vivo (2). Traditional NSAIDs also inhibit COX-2 in the vasculature, but the associated risk of thrombosis is mitigated to some extent by inhibition of formation of thromboxane A2 (TxA2), a COX-1-derived PG released by activated platelets that promotes platelet activation and aggregation (1,3). Thus, the risk of thrombosis for a particular NSAID is dependent upon its relative selectivity for COX-2 over COX-1 (3,6). In addition to their effects on vascular PG production, all NSAIDs inhibit renal PG formation, resulting in sodium retention and hypertension, which may further augment cardiovascular risk (1,3,7).

Currently, it is recommended that NSAIDs be avoided or used only for a limited duration in patients classified as high cardiovascular risk (8). These recommendations are supported by studies demonstrating that even short-term NSAID use increased the incidence of cardiovascular events in patients undergoing coronary artery bypass grafting (9,10) and following a myocardial infarction (11,12). However, long-term treatment with COX-2-selective NSAIDs also increased the incidence of cardiovascular events in patients considered to be at low baseline risk (13,14), consistent with risk transformation due to atherogenesis and indicating traditional cardiovascular risk factors alone are not sufficient to guide therapeutic decisions. Thus, additional studies are necessary to define comprehensively the factors that modify the cardiovascular risk of NSAID use and facilitate the progressive personalization of NSAID therapy.