As manufacturers Pfizer prepare to launch Viagra in Europe and Australia in coming weeks, statistics posted on the US Food and Drug Administration's (FDA) Website have identified 123 deaths linked with the drug, of which 69 were in the US.

Most of the US deaths were linked to heart attacks and related medical conditions, the FDA said.

The deaths could be a result of "physical exertion"

Some 25 of the victims died within four or five hours of taking the drug, and 18 of these succumbed during or immediately after intercourse, according to the FDA.

Almost three-quarters of the 69 Americans who died had one or more risk factors for cardiovascular disease such as high blood pressure, diabetes or obesity, contraindicating the use of Viagra.

Of the remaining 54 fatalities, 12 were foreign deaths and 30 were unverifiable. Reporters said they did not know if the drug had been used in the other 12 cases.

Bestseller

Viagra is one of the most widely prescribed medicines ever.

Over 3.6 million prescriptions have been written for the drug in the US since its launch.

The product is in the final stages of approval by the European Commission and is likely to become available in all European Union member states in September.

The European Agency for Evaluation of Medicinal Products (EMEA) has recommended to the EC that the sexual dysfunction drug be licensed.

Professor Bass: "We've recommended that Viagra can be licensed"

But the head of the EMEA's human medicines unit, Professor Rolf Bass, added: "We're certainly reviewing very carefully the situation developing in the US."

Physical exertion

Theories as to why the deaths in the US occurred point not to a direct side-effect of taking the drug itself but to a strain on the heart from the "physical exertion" of sexual activity.

Speaking on Radio 4's Today programme, Professor Bass said it is difficult to give proof that this argument is true.

"But it is certainly the argument put forward from the company and accepted so far by the US FDA, and by their explanation it wouldn't make any difference whether you shovel snow in the winter or cut trees," he said.

Patient information has been put out in advance of the European launch because of the massive public interest in Viagra, Professor Bass said.

The labelling "contains information and warnings relating to the heart and sensations and so forth which are not in the American labelling", he said.

Viagra for Australians

Viagra is scheduled to be launched in Australia within weeks.

Australian Health Minister Michael Wooldridge predicted that sales would probably outstrip those of the century's other wonder drug, penicillin.

But before the drug can go on sale, Pfizer Australia will have to alter its packaging to include health warnings.

Similar to the European labelling, the revised patient information will warn: "The use of Viagra in men with cardiac disease has been associated with sudden death. The concomitant use of nitrates and Viagra is contraindicated."

'Unprecedented demand'

Mr Wooldridge said the approval process had been fast-tracked for fear of a burgeoning black market and sales of the drug over the Internet.

"If overseas experience is anything to go by, there will be unprecedented demand for it," Mr Wooldridge said.

The drug will be expensive to deter men from indulging beyond the prescribed dosage.