Celecoxib

Celecoxib

Celecoxib (INN) is a non-steroidal anti-inflammatory drug (NSAID) used in the treatment of osteoarthritis, rheumatoid arthritis, acute pain, painful menstruation and menstrual symptoms, and to reduce numbers of colon and rectum polyps in patients with familial adenomatous polyposis. It is marketed by Pfizer. It has the brand name Celebrex and Celebra (in other countries) for arthritis and Onsenal for polyps. Celecoxib is available by prescription in capsule form.

Indications

Celecoxib is licensed for use in osteoarthritis, rheumatoid arthritis, acute pain, painful menstruation and menstrual symptoms, and to reduce the number of colon and rectal polyps in patients with familial adenomatous polyposis. It was originally intended to relieve pain while minimizing the gastrointestinal adverse effects usually seen with conventional NSAIDs. In practice, its primary indication is in patients who need regular and long term pain relief: there is probably no advantage to using celecoxib for short term or acute pain relief over conventional NSAIDs. In particular, the pain relief offered by celecoxib is similar to that offered by paracetamol.

Availability

Pfizer sells Celecoxib under the brand name Celebrex. Celecoxib is not currently available as a generic in the United States, because the intellectual property is still controlled by Pfizer. However, in other countries, including India and the Philippines, it is legally available as a generic under the brand names Cobix, Celcoxx, and others.

Pharmacology

Celecoxib is a highly selective COX-2 inhibitor and primarily inhibits this isoform of cyclooxygenase (inhibition of prostaglandin production), whereas traditional NSAIDs inhibit both COX-1 and COX-2. Celecoxib is approximately 7.6 times more selective for COX-2 inhibition over COX-1. In theory, this specificity allows celecoxib and other COX-2 inhibitors to reduce inflammation (and pain) while minimizing gastrointestinal adverse drug reactions (e.g. stomach ulcers) that are common with non-selective NSAIDs.

Dosing

The usual adult dose of celecoxib is 100 to 200mg once or twice a day. The lowest effective dose should be used.

Adverse effects

Gastrointestinal ADRs

In theory the COX-2 selectivity should result in a significantly lower incidence of gastrointestinal ulceration than traditional NSAIDs. The main body of evidence touted to support this theory were the preliminary (6 month) results of the Celecoxib Long-term Arthritis Safety Study (CLASS) as published in 2000, which demonstrated a significant reduction in the combination of symptomatic ulcers plus ulcer complications in those taking celecoxib versus ibuprofen or diclofenac, provided they were not on aspirin (Silverstein et al, 2000). However, this was not significant at 12 months (full study length). It should be noted that this study used a very high dose of Celebrex, 800mg daily (400mg twice a day).

Allergy

Celecoxib contains a sulfonamide moiety and may cause allergic reactions in those allergic to other sulfonamide-containing drugs. This is in addition to the contraindication in patients with severe allergies to other NSAIDs.

Risk of heart attack and stroke

There has been much concern about the possibility of increased risk for heart attack and stroke in users of NSAID drugs, particularly COX-2 selective NSAIDs such as celecoxib, since the withdrawal of the COX-2 inhibitor rofecoxib (Vioxx) in 2004. Like all NSAIDs on the U.S. market, celecoxib carries an FDA-mandated "black box warning" for cardiovascular and gastrointestinal risk. In February 2007, the American Heart Association warned that celecoxib should be used "as a last resort on patients who have heart disease or a risk of developing it", and suggested that paracetamol (acetaminophen), or certain older NSAIDs, such as naproxen, may be safer choices for pain relief in these patients.

The cardiovascular risks of celecoxib are controversial, with apparently contradictory data produced from different clinical trials. In December 2004, "APC," the first of two trials of celecoxib for colon cancer prevention, found that long-term (33 months) use of high-dose Celebrex (400 and 800mg daily) demonstrated an increased cardiovascular risk compared with placebo. A similar trial, named PreSAP, did not demonstrate an increased risk. Still, the APC trial, combined with the recent Vioxx findings, suggested that there might be serious cardiovascular risks specific to the COX-2 inhibitors. On the other hand, a large Alzheimers prevention trial, called ADAPT, was terminated early after preliminary data suggested that the nonselective NSAID naproxen, but not celecoxib, was associated with increased cardiovascular risk. In April 2005, after an extensive review of data, the FDA concluded that it was likely "that there is a 'class effect' for increased CV risk for all NSAIDs.

Two studies on the cardiovascular risks of celecoxib and other NSAIDs were meta-analyses, published in 2006. The first of these, published in the British Medical Journal, looked at the incidence of cardiovascular events in all previous randomized controlled trials of COX-2 inhibitors, as well as some trials of other NSAIDs. The authors concluded that a significant increased risk did exist for celecoxib, as well as some other selective and nonselective NSAIDS. However, the increased cardiovascular risk in celecoxib was only noted at daily doses of 400 mg or greater. A second meta-analysis published in the Journal of the American Medical Association, which included observational rather than randomized studies (mostly at lower doses) did not find an increased cardiovascular risk of celecoxib vs placebo.

To more conclusively establish the true cardiovascular risk profile of celecoxib, Pfizer has agreed to fund a large, randomized trial specifically designed for that purpose. The trial, centered at the Cleveland Clinic, has a planned enrollment of 20,000 high-risk patients. Celecoxib will be compared to the non-selective NSAIDS naproxen and ibuprofen. Since all patients have arthritis, ethical considerations make it difficult to have a placebo group. This trial has just begun enrollment according to the Clinical Trials database, and is not scheduled to be completed until 2010. Ultimately, this trial will help answer the question as to whether Celebrex has a riskier cardiovascular profile compared to naproxen or ibuprofen.

History

Celecoxib was developed by G. D. Searle & Company and co-promoted by Monsanto (parent company of Searle) and Pfizer under the brand name Celebrex. Monsanto merged with Pharmacia, from which the Medical Research Division was acquired by Pfizer, giving Pfizer ownership of Celebrex. The drug was at the core of a major patent dispute that was resolved in Searle's favor (later Pfizer) in 2004. In University of Rochester v. G.D. Searle & Co., 358 F.3d 916 (Fed. Cir. 2004), the University of Rochester claimed that United States Pat. No. 6,048,850 (which claimed a method of inhibiting COX-2 in humans using a compound, without actually disclosing what that compound might be) covered drugs such as celecoxib. The court ruled in favor of Searle, holding in essence that the University had claimed a method requiring, yet provided no written description of, a compound that could inhibit COX-2 and therefore the patent was invalid.

After the withdrawal of rofecoxib (Vioxx) from the market in September 2004, Celebrex enjoyed a robust increase in sales. However, the results of the APC trial in December of that year raised concerns that Celebrex might carry risks similar to those of Vioxx, and Pfizer announced a moratorium on direct-to-consumer advertising of Celebrex soon afterwards. After a significant drop, sales of Celebrex have recovered, and reached $2 billion in 2006. Pfizer resumed advertising Celebrex in magazines in 2006, and resumed television advertising in April of 2007 with an unorthodox, 2 1/2 minute advertisement which extensively discussed the adverse effects of Celebrex in comparison to other anti-inflammatory drugs. The ad drew criticism from the consumer advocacy group Public Citizen, which called the ad's comparisons misleading. Pfizer has responded to Public Citizens concerns with assurances that they are truthfully advertising the risk and benefits of Celebrex as set forth by the FDA.

In late 2007, Pfizer released another US television ad for Celebrex, which also discussed Celecoxib's adverse effects in comparison to other anti-inflammatory drugs.

Research into cancer prevention

The role that celecoxib might have in reducing the rates of certain cancers has been the subject of many studies. However, given the side effects of anti-COX-2 on rates of heart disease, there is no current medical recommendation to use this drug for cancer reduction.

  • Colorectal cancer risk is clearly reduced in people regularly taking a NSAID like aspirin or celecoxib. In addition, some epidemiological studies, and most preclinical studies pointed out that specific COX-2 inhibitors like celecoxib are more potent and less toxic than "older" NSAIDs. Twelve carcinogenesis studies support that celecoxib is strikingly potent to prevent intestinal cancer in rats or mice (data available on the Chemoprevention Database). Small-scale clinical trials in very high risk people (belonging to FAP families) also indicate that celecoxib can prevent polyp growth. Hence large-scale randomized clinical trials were undertaken and results published by N.Arber and M.Bertagnolli in the New England Journal of Medicine, August 2006 Results show a 33 to 45% polyp recurrence reduction in people taking 0.4-0.8 g celecoxib each day. However, serious cardiovascular events were significantly more frequent in the celecoxib treated groups (see above, cardiovascular toxicity). Aspirin shows a similar (and possibly larger) protective effect, has demonstrated cardioprotective effects and is significantly cheaper, but there have been no head-to-head clinical trials comparing the two drugs.

Research into cancer treatment

Different from cancer prevention, cancer treatment is focused on the therapy of tumors that have already formed and have established themselves inside the patient. Many studies are ongoing to determine whether celecoxib might be useful for this latter condition. However, during molecular studies in the laboratory, it became apparent that celecoxib could interact with other intracellular components besides its most famous target, cyclooxygenase 2 (COX-2). The discovery of these additional targets has generated much controversy, and the initial assumption that celecoxib reduces tumor growth primarily via the inhibition of COX-2 became contentious.

Certainly, the inhibition of COX-2 is paramount for the anti-inflammatory and analgesic function of celecoxib. However, whether inhibition of COX-2 also plays a dominant role in this drug’s anticancer effects is unclear. For example, a recent study with malignant tumor cells showed that celecoxib could inhibit the growth of these cells in vitro, but COX-2 played no role in this outcome; even more strikingly, the anticancer effects of celecoxib were also obtained with the use of cancer cell types that don’t even contain COX-2.

Additional support for the idea that other targets besides COX-2 are important for celecoxib’s anticancer effects has come from studies with chemically modified versions of celecoxib. Several dozen analogs of celecoxib were generated with small alterations in their chemical structures. Some of these analogs retained COX-2 inhibitory activity, whereas many others didn’t. However, when the ability of all these compounds to kill tumor cells in cell culture was investigated, it turned out that the antitumor potency did not at all depend on whether or not the respective compound could inhibit COX-2, showing that inhibition of COX-2 was not required for the anticancer effects. One of these compounds, 2,5-dimethyl-celecoxib, which entirely lacks the ability to inhibit COX-2, actually turned out to display stronger anticancer activity than celecoxib itself.

References

Footnotes

External links

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