A drug used to treat multiple sclerosis (MS) patients in New Zealand can cause fatal brain infections, and new evidence from the United States shows the potential risk increases each time it is administered.
Medsafe said the drug Tysabri -- sold here as Natalizumab -- is still needed by some patients.
Senior advisor Susan Kenyon said manufacturer Biogen Idec advised doctors about a link between the drug and the brain infections in 2008 -- shortly after Medsafe approved the drug in this country.
She said the manufacturer was not obliged to alert the regulator.
Now it is waiting on Biogen to update datasheets for the medicine on the Medsafe website, with advice on the potential for increasing risks with increasing used of the drug.
Nine patients in New Zealand are taking Natalizumab as part of a clinical trial -- due to end in 2011 -- and a further eight are being prescribed the drug.
Dr Kenyon told NZPA that so far, there have been no reports of adverse reactions here.
Multiple sclerosis was a serious condition for which there was no cure, she said.
"While the prognosis is difficult to predict, some patients suffer significant disability. There is a need for effective treatments to slow disease progression."
About half the patients with the "relapsing remitting" form of the disease go on to get secondary progressive MS within 20 years, where the disease steadily worsens.
Symptoms can include muscle weakness and spasms, difficulties with coordination, balance, speech, swallowing, sight, continence, and thinking.
Originally approved by the Food and Drug Administration (FDA) in the United States in 2004, the drug was temporarily withdrawn in 2005 because of its links to brain infections in MS patients. It was re-launched in 2006.
The drug was approved for prescription use in New Zealand -- where 3500 people have been diagnosed with MS -- in February 2008.
Dr Kenyon said Medsafe had been told that a letter was sent later in 2008 by the manufacturer to New Zealand doctors about the potential link to a rare viral disease -- progressive multifocal leukoencephalopathy (PML).
It was the company's responsibility to update the data sheet, which already includes information on a risk of PML.
"The further update is to include warnings that the risk is dose-related," said Dr Kenyon.
The FDA has said the risk of developing PML appeared to increase with the number of infusions received by a patient.
For the 13 patients with confirmed PML last September, the number of monthly infusions ranged from 12 to 35, and the average number of infusions received before diagnosis of PML was 25.
The FDA now said it had received 31 confirmed cases of PML up to last month.
One MS patient who signed up for the New Zealand clinical trial was painter and sculptor, Carole Hebberd, of Cambridge, who was diagnosed 14 years ago at the age of 39.
The drug has kept her illness fairly stable, though she still has some symptoms.
"I stay very stable and it's not progressing," Mrs Hebberd told the Waikato Times.
"The only thing that worries me is what happens when this trial ends, in 2011," said the mother of two, who said the drug -- which would cost $41,000 a year to buy -- should be funded by Pharmac.
