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VIOXX mechanism (COX-1 & 2) explained

COX-2 INHIBITORS  Mechanism, risk, etc.


Article explains the action of COX-1 & COX-2 inhibitors (what was used to justify VIOXX and Celebrex) the drugs that accounted for over 60,000 deaths--jk.





Published online before print March 21, 2005, doi:10.1161/01.CIR.0000160005.90598.41

(Circulation. 2005;111:1713-1716.)
2005 American Heart Association, Inc.;111/13/1713

AHA Science Advisory (American Heart Association)

The Use of Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

A Science Advisory From the American Heart Association

Joel S. Bennett, MD; Alan Daugherty, PhD; David Herrington, MD, MHS; Philip Greenland, MD; Harold Roberts, MD; Kathryn A. Taubert, PhD

Recent clinical trial data have raised questions about the degree to which patients and their physicians should consider an increased  risk of cardiovascular or cerebrovascular events when selecting medications for pain relief. In September 2004, Merck announced a voluntary worldwide withdrawal of Vioxx (rofecoxib) because of an increased risk of heart attack and stroke. In early December 2004, the US Food and Drug Administration (FDA)  announced a "black box" warning for Bextra (valdecoxib), stating that its use in patients undergoing coronary artery bypass grafting is contraindicated. A week later, the National Institutes of Health suspended the use of Celebrex (celecoxib) in the APC (Adenoma Prevention with Celecoxib) clinical trial because of increased cardiovascular events. The drug was not removed from the market, but the FDA advised physicians to consider alternate therapy or to use the smallest effective dose of Celebrex. Three days later, the National Institutes of Health announced that the ADAPT (Alzheimer’s Disease Anti-inflammatory Prevention Trial) showed an increase in the risk of cardiovascular events in patients given naproxen but not in those given celecoxib; the trial was halted. At the end of 2004, the FDA issued a Public Health Advisory summarizing the agency’s recent recommendations concerning the use of the nonsteroidal anti-inflammatory drug products (NSAIDs) Vioxx, Bextra, Celebrex, and naproxen.1 Quoting from the Public Health Advisory:

  • "Physicians prescribing Celebrex (celecoxib) or Bextra (valdecoxib) should consider this emerging information when weighing the benefits against risks for individual patients. Patients who are at a high risk of gastrointestinal (GI) bleeding, have a history of intolerance to non-selective NSAIDs, or are not doing well on non-selective NSAIDs may be appropriate candidates for COX-2 selective agents.
  • Individual patient risk for cardiovascular events and other risks commonly associated with NSAIDs should be taken into account for each prescribing situation.
  • Consumers are advised that all over-the-counter (OTC) pain medications, including NSAIDs, should be used in strict accordance with the label directions. If use of an OTC NSAID is needed for longer than ten days, a physician should be consulted."

We support these recommendations and here provide a brief scientific background for them. We also expand on the relevance of these recommendations to patients with or at risk for cardiovascular disease.

MECHANISM OF ACTION:  [T]he primary property of this class of drugs is the inhibition of cyclooxygenase (COX). COX enzymes have 2 major classes. COX-1 is broadly considered to be expressed constitutively (constantly) in most tissues, whereas COX-2 is induced in inflammation. Both COX-1 and -2 enzymes use arachidonic acid to generate the same product, prostaglandin H2 (PGH2). A number of enzymes further modify this product to generate bioactive lipids (prostanoids), including prostacyclin, thromboxane A2, and prostaglandins D2, E2, and F2, which influence immune, cardiovascular, GI, renovascular, pulmonary, central nervous system, and reproductive function. The COX-2 inhibitors vary in their selectivity for the COX-2 versus the COX-1 enzyme (for medications currently or formerly on the market in the US, rofecoxib > valdecoxib > parecoxib > celecoxib). Other COX-2 inhibitors are under development and may be introduced onto the US market in the future. The differences in the biological effects of COX inhibitors are a consequence of the degree of selectivity for COX-2 versus COX-1 and tissue-specific variations in the distribution of COX and related enzymes that convert prostaglandin H2 into specific prostanoids. For example, several prostanoids, including prostaglandin E2 and prostacyclin, are both hyperalgesic (ie, elicit an increased sense of pain) and gastroprotective. Thus, nonselective COX inhibition with agents such as aspirin, ibuprofen, indomethacin, and naproxen, which inhibit both COX-1 and COX-2 enzymes, provides effective pain relief for inflammatory conditions but carries with it a risk for erosive gastritis and GI bleeding. Selective COX-2 inhibitors (valdecoxib, rofecoxib, celecoxib, and others yet in development) were developed to minimize GI toxicity because of the relative paucity of COX-2 expression in the GI tract and the relative abundance of COX-2 expression in inflamed and painful tissues.  [The comparison is between a coated medication which dissolves in the intestines and that of uncoated—usually aspirin--which with prolonged usage in high doses produces a statistically significant upper GI issues—heartburn and bleeding.  Coated aspirin is not used in these comparisons—jk]  

In the cardiovascular system, the products of COX regulate complex interactions between platelets and the vessel wall. Prostacyclin is the dominant prostanoid produced by endothelial cells.2,3 In addition to producing local smooth muscle cell relaxation and vasodilation, prostacyclin can also interact with platelet IP receptors, thereby antagonizing aggregation. Platelets contain only COX-1, which converts arachidonic acid to the potent proaggregatory, vasoconstrictive eicosanoid thromboxane A2 (TXA2), the major COX product formed by platelets. Nonselective COX inhibition with aspirin is effective for arterial thrombosis because of its ability to reduce COX-1–dependent production of platelet TXA2; however, selective inhibition of COX-2 could produce a relative reduction in endothelial production of prostacyclin, but leave the platelet production of TXA2 intact. It has been speculated that this imbalance of hemostatic prostanoids may increase the risk for cardiovascular events.4,5 COX-2 inhibitors, like NSAIDs, also raise blood pressure slightly, and in one study the incidence of heart failure was significantly increased compared with placebo.6 Prostacyclin may also retard the pathogenesis of atherosclerosis,4 and inhibition of prostacyclin with a COX-2 inhibitor has been predicted to promote lesion formation4; however, results in different mouse models of atherosclerosis have been contradictory.7–13  The extent to which these effects may contribute to adverse cardiovascular effects of COX-2 is unclear. However, renal function and blood pressure should be monitored in subjects taking COX-2 inhibitors and extra caution should be taken when giving these drugs to subjects with preexisting hypertension, renal disease, and heart failure.

In mid-February 2005, the FDA conducted an extensive review of all of the data concerning the cardiovascular risks of selective and nonselective COX inhibitors. It is anticipated that more information and guidance are forthcoming as a result of this meeting. In the meantime, practical guidance is needed by patients (and their physicians) who are making decisions about the use of these drugs for pain relief, especially if the patients are also at high risk for cardiovascular events. The importance of these issues for patients with or at risk for cardiovascular or cerebrovascular disease cannot be overstated because it is in these patients that the absolute risks are likely the greatest.

From the patient’s—and the physician’s—perspective, the decision turns on balancing the risks and benefits of medications for pain relief. Of course, risks and benefits are not unique to these medications, but their use highlights the issues to be considered. The following lists several issues that should be considered when treatment decisions are made concerning pain medications in patients with or at high risk for cardiovascular disease.

RISK RATIOS:  Recently published results of three randomized, placebo-controlled clinical trials, although not primarily designed to evaluate the effects of COX-2 inhibitors on cardiovascular outcomes, provide some estimates of absolute risk associated with COX-2 inhibitor use in various populations. The APC trial included patients with a history of colorectal neoplasia who were given two different doses of celecoxib or placebo. There was a 1% composite cardiovascular end point of death from cardiovascular causes, nonfatal myocardial infarction, nonfatal stroke, or nonfatal heart failure in the placebo group, compared with a 2.3% composite cardiovascular end point in patients receiving a total dose of 400 mg per day celecoxib and a 3.4% composite cardiovascular end point in those taking 800 mg celecoxib per day.14 The APPROVE trial included patients with a history of colorectal adenomas who received long-term rofecoxib or placebo. An increased risk of thrombotic events was observed in the treatment group after 18 months of treatment (0.78 events/100 patient-years versus 1.5 events/100 patient-years in the rofecoxib group).6 Finally, a study in post-CABG patients compared valdecoxib/parecoxib with placebo and found that cardiovascular events were more frequent in the treatment group (2.0% versus 0.5% for the placebo group).15 [1% VS 2.3% and 3.4% for the higher dosage of celecoxib, and similar numbers for other studies when comparing to placebo; viz., a three fold increase.  Since the damage to blood vessels is accumulative, the percentage would increase with time—jk]



  1. US Food and Drug Administration. Public Health Advisory: Non-Steroidal Anti-Inflammatory Drug Products (NSAIDS). Available at: Accessed February 4, 2005.

  1. Bunting S, Gryglewski R, Moncada S, Vane JR. Arterial walls generate from prostaglandin endoperoxides a substance (prostaglandin X) which relaxes strips of mesenteric and coeliac arteries and inhibits platelet aggregation. Prostaglandins. 1976; 12: 897–913.[CrossRef][Medline]

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  1. Solomon SD, McMurray JJV, Pfeffer MA, Wittes J, Fowler R, Finn P, Anderson WF, Zauber A, Hawk E, Bertagnolli M. Cardiovascular risk associated with celecoxib in a clinical trial for colorectal adenoma prevention. N Engl J Med 2005;352. Available at: Accessed February 15, 2005.

  1. Nussmeier NA, Whelton AA, Brown MT, Langford RM, Hoeft A, Parlow JL, Boyce SW, Verburg KM. Complications of the COX-2 inhibitors parecoxib and valdecoxib after cardiac surgery. N Engl J Med 2005;352. Available at: Accessed February 15, 2005.

  1. Chan FK, Chung SC, Suen BY, Lee YT, Leung WK, Leung VK, Wu JC, Lau JY, Hui Y, Lai MS, Chan HL, Sung JJ. Preventing recurrent upper gastrointestinal bleeding in patients with Helicobacter pylori infection who are taking low-dose aspirin or naproxen. N Engl J Med. 2001; 344: 967–973.[Abstract/Free Full Text]

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