The US Food and Drug Administration on May 21 approved Vioxx for treating both osteoarthritis and acute pain. Vioxx is part of a new class of drugs called cox-2 inhibitors that aim to provide the same relief as existing anti-inflammatory drugs such as ibuprofen, but without the older drugs' tendency to cause bleeding ulcers.

Vioxx will compete with Monsanto Co. and Pfizer Inc.'s Celebrex arthritis medicine, the first drug in the new cox-2 class to get FDA approval.

Celebrex, which was introduced at the beginning of the year, has enjoyed one of the fastest new-drug launches in industry history, although its sales growth has slowed recently. Now, Merck will try to steal market share away from Celebrex as well as older drugs that still make up the majority of the market.

Success is crucial for Merck. Several of the New Jersey-based company's big-selling drugs areset to lose patent protection in 2000 and 2001. Merck hopes Vioxx will help offset revenue that is likely to be lost when the patents expire on the older drugs.

Overall, Celebrex and Vioxx are similar, but Merck is expected to try to take advantage of its broader FDA approval: Vioxx was approved for treating both acute pain and osteoarthritis, while Celebrex was approved only for arthritis. Merck also maintains that Vioxx is a "true" once-a-day pill and has a longer duration of action than Celebrex, which is taken either once or twice a day. Merck said it is conducting comparative studies to prove this.Monsanto officials said Celebrex works just fine when taken once a day. Moreover, Monsanto noted that unlike Vioxx, Celebrex is approved for treating rheumatoid arthritis, the most severe form of the disease.

Jeffrey Chaffkin, an industry analyst at PaineWebber Inc., says the battle will ultimately be decided by marketing clout because, "despite the hype, there is not all that much difference between thetwo drugs." In the end, he predicts, Celebrex will retain the largest market share because of its head start, but Vioxx will also do well because there's room in the market for two major players.

In clinical trials, Vioxx was as effective as older anti-inflammatory drugs such as ibuprofen in relieving symptoms of osteoarthritis. But the tests showed that significantly fewer patients taking Vioxx got small early-stage ulcers than those who took ibuprofen. Nevertheless, the FDA included in Vioxx's label a standard warning about the potential of anti-inflammatory drugs to cause ulcers.

This warning, which is also on Celebrex's label, is expected to stand until longer-term human studies, under way at both Monsanto and Merck, conclusively prove that cox-2 drugs cause fewer bleeding ulcers and other serious stomach side-effects than the older drugs.

Vioxx will cost about $70 a month, and will be available in US stores in about a week. Side-effects are generally mild and include diarrhoea and upper-respiratoryinfection, Merck said.

--The Asian Wall Street Journal