The sudden withdrawal of the drug, which is used to treat attention deficit hyperactivity disorder (ADHD), was caused by an order from Health Canada, the Canadian drug authority, after reports indicated that 14 children and six adults had died suddenly after taking regular doses of the drug. Of the deaths, 12 were due to strokes, two of which occurred in children.
The authority undertook a further study comparing Adderall with rival drugs for ADHD, which showed the incidence of adverse reactions that could lead to death was higher with Adderall than with other treatments. About 11,000 patients are now being advised to consult their doctors about finding alternative drugs.
Shares in Shire crashed 16 per cent on the news, as fears spread that the Food and Drug Administration (FDA) would take similar action in the United States.
The FDA, however, said that although it had seen the same data as Health Canada regarding the deaths, it does not believe the information gives rise to sufficient safety concerns to warrant revoking approval for Adderall. This helped the shares in the company slightly and they closed down 10 per cent at 577.5p.
Shire said it "strongly disagrees" with Health Canada's decision. Matthew Emmens, the chief executive, said: "We are surprised by this action. Shire remains confident in the safety and efficacy of Adderall."
The 20 deaths - which Health Canada said occurred outside the country - happened over 10 years, during which time 38 million prescriptions for Adderall had been written.
Frances Cloud, an analyst at Nomura, said: "These deaths were extremely rare. Since Canadian sales of Adderall were only $10m (pounds 5m), the financial impact of this decision is negligible. Were the FDA to remove approval, it would be disastrous for Shire, which obtains more than 40 per cent of its sales from this product. But this is extremely unlikely."
Tony Butler, at Lehman Brothers, said rivals such as the US drug maker Eli Lilly could benefit from Canada's move. "We view the US impact for [Lilly's ADHD treatment] Strattera could be positive, but not necessary imminent," he added.
The FDA said yesterday that it had evaluated the risk of sudden death with Adderall before giving it approval, but it does not believe the number of deaths reported is greater than the number of sudden deaths that would be expected to occur in the population.
It believes new labelling requirements it asked Shire to introduce in September, which beefed up warnings on the danger of taking the drug if the patient has heart problems, is adequate for the risks involved.
Adderall had been on sale in Canada for 12 months. It is not sold in Europe.Reuse content