Nonsteroidal anti-inflammatory drugs represent the most commonly used medications for the treatment of pain and inflammation, but numerous well-described side effects can limit their use. Cyclooxygenase-2 (COX-2) inhibitors were initially touted as a therapeutic strategy to avoid not only the gastrointestinal but also the renal and cardiovascular side effects of nonspecific nonsteroidal anti-inflammatory drugs. However, in the kidney, COX-2 is constitutively expressed and is highly regulated in response to alterations in intravascular volume. COX-2 metabolites have been implicated in mediation of renin release, regulation of sodium excretion, and maintenance of renal blood flow. This review summarizes the current state of knowledge about both renal and cardiovascular side effects that are attributed to COX-2 selective inhibitors.Clin J Am Soc Nephrol 1: 236 -245, 2006236 -245, . doi: 10.2215 N onsteroidal anti-inflammatory drugs (NSAID) are the most commonly used class of medications for the treatment of pain and inflammation and represent one of the most common classes of medications used worldwide, with an estimated usage of Ͼ30 million per day (1). Nonselective NSAID inhibit both constitutive cyclooxygenase-1 (COX-1) and inducible cyclooxygenase-2 (COX-2), the rate-limiting enzymes that are involved in production of prostaglandins and thromboxane. In addition to their role in inflammation, prostaglandins are important regulators of vascular tone, salt and water balance, and renin release, and nonselective NSAID exhibit adverse effects, including salt retention and reduced GFR, which may elevate BP or make pre-existing hypertension worse (2). It has been estimated that as many as 2.5 million Americans experience NSAID-mediated renal effects yearly (3). Risk factors that predispose to NSAID-induced renal functional alterations include age Ͼ65 yr, cardiovascular disease, diabetes, male gender, high NSAID dosage, and concurrent use of other nephrotoxic drugs (3). Up to 20% of patients who take nonselective NSAID and have more than one of these risk factors may manifest alterations in renal function.In addition to renal side effects, nonselective NSAID have long been known to predispose to gastrointestinal (GI) toxicity. It has been estimated that one third of patients who taking long-term nonselective NSAID develop endoscopically proven gastric or duodenal ulcers (4). The risk for serious bleeding from these lesions is somewhat lower, with approximately 100,000 hospitalizations for GI complications of NSAID (5). One study estimated that nonselective NSAID-induced GI abnormalities constitute the 15th leading cause of death in the United States (6). The premise that COX-1 performs cellular "housekeeping" functions for normal physiologic activity and is the predominant isoform expressed in platelets and the GI tract, whereas COX-2 acts at inflammatory sites, led to the development of COX-2 selective inhibitors. It also was originally hypothesized that the renal effects of nonselective NSAID were also linked to COX-...