DRUG FIRM Elan has reported a 22 per cent rise to 31,800 in the number of patients using its multiple sclerosis (MS) treatment Tysabri at the end of June, compared with the first three months of the year.

In a statement yesterday, the biotechnology company said 17,800 of the patients currently prescribed the drug were based in the US, with 13,400 patients in the remaining 35 countries in which use of the drug is approved.

Approximately 6,600 have been on the drug for at least 18 months, the company added.

A further 600 people are taking the drug as part of global clinical trials.

The company also said that in the two years since the drug was reintroduced in the US there have been no been "no confirmed cases" of progressive multifocal leukoencephalopathy, a fatal brain infection.

Elan and its US partner Biogen withdrew Tysabri in February 2005 after two patients developed infections. The companies jointly market the product.

Tysabri returned to the market in July 2006 after the Federal Drug Administration decided that the benefits of slowing relapsing forms of multiple sclerosis from the drug outweighed the risks.

It operates by blocking white blood cells from crossing into the brain and attacking nerves there.

Davy analyst Jack Gorman said the patient numbers were impressive and supported his full-year revenue forecast of $842 million.

He said the data suggested that 438 patients a week were being prescribed the drug, accelerating from the 392 per week recorded at the end of the first quarter.

"The acceleration was driven for the most part by Tysabri's performance outside the US, a recurring theme in recent quarters," he added.

In the US it is estimated that a year's supply of the drug could cost approximately $30,000.

Elan will report its second quarter results this week.

Biogen yesterday reported an 11 per cent rise in second-quarter profits on higher sales of Tysabri, its fastest-growing medicine. The company has also raised its 2008 forecast.

Net income climbed to $207 million, or 70 cents a share, from $186.1 million, or 54 cents, a year earlier, the company said in a statement. Excluding certain costs, Biogen earned 91 cents, beating estimates. Revenue rose 28 per cent to $993.4 million as more doctors prescribed Tysabri.

Biogen and Elan have set a target of 100,000 patients using Tysabri by 2010.