US doctors are proving more wary than many had expected about prescribing the Elan's multiple sclerosis drug Tysabri.
The drug was relaunched in July after being suspended because of safety concerns.
Over the past month or so, analysts have drawn down their 2006 sales forecasts as it becomes clear that doctors wary of the risk posed by the rare but potentially fatal brain disease PML are reserving the drug as a treatment of last resort.
The drug, which is made by Elan and Biogen, had been expected by some analysts to generate sales this year of more than $100 million, but those figures have dropped dramatically.
Ian Hunter, an analyst at Goodbody stockbrokers in Dublin, said that he has cut his full-year Tysabri forecast to $25.7 million from $78 million, in part because of continuing safety concerns and the complexity of reimbursement systems in Europe.
A survey of 63 neurologists conducted by Reuters Primary Research indicates that in 2006 Tysabri will be used in less than 1 per cent of multiple sclerosis patients - translating into revenue of under $30 million.
Since July, only 47 of more than 8,500 patients treated by the physicians had used Tysabri, even though more than 700 patients had discussed using it, according to the report.
And more than 75 per cent of the patients who had used Tysabri prior to its 2005 suspension have decided not to use it since its reintroduction, the survey showed.
In taking the rare decision to allow a withdrawn drug back onto the market, the US Food and Drug Administration was partially influenced by calls from patients who said they were willing to take the risk of contracting progressive multifocal leukoencephalopathy because of the potential benefits of the drug.