In Australia, arthritis sufferers have been told to keep taking the painkiller Celebrex despite the drug’s manufacturer finding.

Pfizer Inc has announced that a US study found patients taking 400 mg to 800 mg of the drug daily in long-term cancer prevention trials had a two-and-a-half times greater risk of experiencing major heart problems than those not taking the drug.

Celebrex is part of a class of drugs called COX-2 inhibitors and is popular for its effectiveness in treating the pain of arthritis and other ailments and used by tens of thousands of Australians.

Despite the announcement from Pfizer, Australian Medical Association president Bill Glasson urged Australians taking the drug not to panic.

Dr Glasson said most arthritis sufferers would take doses of 100 mg to 200 mg of the drug, which was much less than the doses used in the US study.

“We are telling people to talk to their GP and not to go off the drug, and reminding people that they will be taking one quarter of the dose that people were taking in this particular study,” he said.

Dr Glasson said the study was also based on people suffering from cancer and was not a study of the broader population, he said.

Dr Glasson said the Therapeutic Drugs Administration (TGA) was reviewing COX-2 inhibitors.

“We are currently reviewing all the literature and all the studies that have been undertaken into COX-2 inhibitors across the board and the TGA in Australia will (soon) be coming out with a recommendation, both in relation to the class of drugs and individual drugs,” he said.

The US Food and Drug Administration said, however, that action could be taken over the findings of one new cancer study, which led to an immediate halt in dosing of Celebrex in the trial. A second new study did not find an increased risk however.

Celebrex is used by 26 million people, according to Pfizer, and is the latest COX-2 type pain drug to face controversy. Vioxx, made by the rival Merck and Co., was withdrawn in September because of the increased risk of heart attacks.

Three US doctors on Friday appealed for doctors to stop prescribing Bextra, another COX-2 painkiller, also made by Pfizer.

News of the Celebrex study sent Pfizer shares slumping but the US firm’s chairman Hank McKinnell said the drug would not be withdrawn.

“Any decision to withdraw a drug has to be made in the context of all of the information,” said Mr McKinnell.

“Until the study results became known to us late last night we saw a very acceptable safety profile for Celebrex. I don’t think this one study, even though it is a large, well-controlled study, characterises the drug in any significant way,” he continued.

A study into the use of Celebrex to prevent benign tumours, or adenomas, showed patients taking 400mg and 800mg of Celebrex daily had an approximately 2.5-fold increased risk of major cardiovascular problem compared to patients on a placebo, according to the US National Cancer Institute.

Based on the “statistically significant” findings, the institute, which sponsored the trial, suspended the dosing of Celebrex. The news was given to Pfizer late Thursday.

A separate study into whether Celebrex can prevent polyps showed no increased risk to the heart.

Pfizer gave the results of the study straight to the US Food and Drug Administration and European regulators as soon as they were received, the company chief said.

In a statement earlier, Mr McKinnell said: “These clinical trial results are new. The cardiovascular findings in one of the studies are unexpected and not consistent with the reported findings in the second study.”

He added that “Pfizer is taking immediate steps to fully understand the results and rapidly communicate new information to regulators, physicians and patients around the world.”

Merck announced a global withdrawal of its painkiller Vioxx on September 30, prompted by a study showing an increased risk of strokes and heart attacks.

Merck’s share price has crumbled and it is now engulfed in lawsuits.

Pfizer shares plunged $US3.23, 11.15 per cent, to close at $US25.75, wiping out $US24.3 billion in Pfizer market capitalisation.

The drug earned $US2.29 billion in the first nine months of 2004 for Pfizer, against $US1.07 billion for the same period last year.

Celebrex is approved in the United States for the treatment of arthritis and pain at recommended doses of 100mg to 200mg daily for osteoarthritis and 200mg to 400mg a day for rheumatoid arthritis.

John Jenkings, a senior official with the US pharmaceutical regulatory body, indicated that the FDA could take action before an agency meeting in February.

He told a press conference that all information about COX-2 drugs would be reviewed. “We are not necessarily waiting until the February advisory meeting to consider what action is warranted,” Mr Jenkins said.

FDA acting commissioner Lester Crawford said earlier the agency had seen only “preliminary results” of the study showing an increased heart risk and it was advising doctors to consider alternative pain drugs for patients and to try to prescribe Celebrex in the lowest effective dose.