The Merck & Co's decision to voluntarily withdraw its patented drug Vioxx (rofecoxib) from the world market on the basis of severe adverse reaction, will pose serious questions over the future of 40 odd brands that are being marketed in India.

The generic versions of rofecoxib, which enjoys a Rs 91 crore cumulative sales in domestic market (MAT, August 2004), would now come under the scanner of Drugs Controller General of India for a possible ban shortly, it is feared.

The companies and their brands that are to be affected include Ranbaxy (Rofibax - Rs 13.5 crore sales), Unichem (Roff - 12.7 crore), Torrent (Torrox - 6.15 crore), Lupin (Rofaday - 5.35 crore), Dr Reddys (Mcrofy - 4.26 crore), Aristo (4.26 crore), Macleods (Rofica - 4 crore), Cipla (Rofixx - 3.75 crore) and Sun (Rofact - 3.5 crore).

The urgency shown by the innovator company to withdraw the product, and the manner in which it wanted the patients to stop using the product and return the unused packets for reimbursement is indicative of the potential ADR that can be caused by rofecoxib it is felt.

According to Merck's own submission, the product poses an increased risk of cardiovascular events (including heart attack and stroke) in patients on Vioxx. The study, which revealed the seriousness of the side effects was published in the US based journal "Circulation" (issue dated April 19, 2004). The study, meant to see if the drug prevents colon cancer was carried out on 2600 subjects and came out with startling observation that the drug (25 mg) doubles the risk of heart attack in placebo and becomes three times more if the dose is doubled to 50 mg. Though Merck had not introduced 50 mg doses in the market, Indian drug authorities are known to have given approval for both the strengths, thereby explaining its presence in the domestic market.

Interestingly, the latest MAT figures show that the Indian rofecoxib brands had shown a 13 % decline in the sales. The decline has been attributed not to the heightened risks attached to the drug, but to the aggressive marketing of other "coxib" brands that are available in the market. The Merck withdrawel is expected to increase the sales of various other 'coxib' brands like etoricoxib, parecoxib and valdecoxib.

Foreseeing the trend, Dr C M Gulhati, editor, Monthly Index of Medical Specialities (MIMS) has warned that all such 'coxibs' are likely to have similar adverse effect and hence should be treated with caution. He explained that the very reason why there are no reported cases of myocardiac risk in these alternatives is the absence of study in that direction.

The inventor's product Vioxx got US FDA approval as a prescription COX-2 selective, non-steroidal anti-inflammatory drug (NSAID) in May 1999. The drug prescribed for the relief of the signs and symptoms of osteoarthritis, for the management of acute pain in adults, and for the treatment of menstrual symptoms, and was later approved for the relief of the signs and symptoms of rheumatoid arthritis in adults and children. In India, the drug was first given marketing approval in June, 2000.