The recent introduction of celecoxib in India is set to be a turning point for the market of antiinflammatory drugs in this country. Belonging to a new and exciting class of COX-2 (cyclooxygenase-2) inhibitors, celecoxib and its congener rofecoxib are two agents that are already revolutionising the treatment of rheumatic and inflammatory disorders in the world’s largest pharmaceutical market, the United States of America. Even before their actual launch, both celecoxib (Celebrex, Searle) and rofecoxib (Vioxx, Merck) were expected to be blockbuster drugs, each with annual sales of 2-3 billion dollars by the year 2002. Current trends show that the drugs are living up to these expectations. In the U.S., Vioxx was approved in May 1999 and by July, U.S. sales totaled 92 million dollars. Celebrex, the first of these COX-2 inhibitors to be launched, may reach an even greater milestone. Some analysts predict that Celebrex will outsell even the well-known impotency treatment Viagra (sildenafil), which in its first month became the fastest-selling drug in history. Viagra’s annual sales are expected to be in the region of 3 billion dollars by the year 2002 and the celecoxib brand could cross this sales figure.
In India too, doctors have indicated their preference for antiinflammatory drugs that hit at the disease and not the patient. For years, cyclooxygenase has been known to be an enzyme responsible for the production of inflammatory mediators, the prostaglandins. Conventional nonsteroidal antiinflammatory drugs (NSAIDs) e.g., aspirin and ibuprofen, owe their antiinflammatory activity to their ability to inhibit cyclooxygenase. However, prostaglandins contribute inter alia to gastric mucosal protection, and such inhibition by NSAIDs comes with adverse effects, most notably, gastric irritation. Selective COX-2 inhibitors such as celecoxib and rofecoxib block inflammation mediated through COX-2, but do not have many of the side effects of nonselective NSAIDs that result from concurrent inhibition of COX-1. Celecoxib 200 mg/day exhibits comparable efficacy to naproxen 500 mg b.i.d. in the treatment of osteoarthritis and rheumatoid arthritis, but with a lower incidence of gastrointestinal adverse effects. Gastrointestinal adverse effects are statistically significantly less when compared to other NSAIDs, including naproxen, diclofenac and ibuprofen. One report says that treatment with celecoxib cuts the rate of gastrointestinal events to just 0.18%, versus 2-4% in patients treated with conventional NSAIDs. Celecoxib also has no action on platelet aggregation and bleeding time.
The concept of selective COX-2 inhibition is not new to the Indian pharmaceutical market. For some time now, meloxicam and nimesulide, which have greater selectivity for COX-2 than conventional NSAIDs, have been accepted and prescribed. Meloxicam and nimesulide brands already account for about Rs 150 crore of a combined antiinflammatory, antirheumatic, analgesic and antipyretic market that is close to Rs 1000 crore. Celecoxib and rofecoxib are even more selective for COX-2 than meloxicam and nimesulide. Surely the new COX-2 inhibitors would further tilt prescribing preferences away from conventional NSAIDs and towards the better tolerated newer antiinflammatory drugs. The Indian antiinflammatory and antirheumatic market owes much of its current modest growth to nimesulide and meloxicam brands, and the introduction of a what is sure to be a horde of new celecoxib brands can only push the growth rate in one direction -- up. With the antiinflammatory, antirheumatic, analgesic and antipyretic markets already having a market share of over 7% in the Rs 13,000+ crore total Indian pharmaceutical market, it would appear worthwhile for a pharmaceutical company to have a presence in this market. Incidentally, in addition to its role in pain and inflammation, celecoxib has also been found to be useful in familial adenomatous polyposis (FAP), to reduce the number of colorectal polyps.
Though the COX-2 inhibitors have been widely touted as safer alternatives to NSAIDs, gastrointestinal adverse effects, including deaths related to gastrointestinal bleeding, have occurred. It is therefore advisable to employ the lowest effective dosage in a patient. In any case, studies involving a higher dose of celecoxib 200 mg BID have not shown any additional benefit over the recommended dosage of 100 mg BID or 200 mg/day. Commoner side effects include headache, dizziness, insomnia, abdominal pain, diarrhoea, dyspepsia, flatulence, nausea, skin rash, and rhinitis. The most common gastrointestinal side effects of celecoxib are dyspepsia, diarrhoea, and abdominal pain. Patients who have a known allergy to other NSAIDs are advised not use celecoxib.
Celecoxib and rofecoxib can be expected to be only the first of many drugs in this class. Other companies, including Smith-Kline Beecham and American Home Products Corporation’s Wyeth-Ayerst, are developing COX-2 inhibitors as well - a widening choice that is sure to bring a smile to the face of patients who till recently could relieve their pain, only to throw their stomachs out of gear.
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This article was published in Pharma Business 2nd June 2000.
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