Shire Pharmaceutical’s share price took a hammering this morning, dropping by as much as 19% during trading on the London Stock Exchange after the UK company revealed that the Canadian regulators had suspended sales of its top-selling ADHD medication, Adderall XR (amphetamine salts extended-release), over concerns it had been linked to cases of sudden death.

Health Canada says it suspended the product after safety reports indicated that 20 people – 14 children and six adults – had died after taking the drug. In addition, 12 people, including two children, suffered a stroke. None of the deaths or strokes occurred in Canada.

Shire was quick to slam the move, saying it strongly disagreed with Health Canada’s conclusions. Although the firm is complying with the request, it is “considering appropriate responsive action.” Chief executive, Matthew Emmens, commented: “We are surprised by this action from Health Canada. Shire remains confident in the safety and efficacy of Adderall XR.” He added that the drug’s availability in the USA is not affected by the latest development. “Shire remains confident in the safety and effectiveness of this drug for the treatment of ADHD when used in accordance with the approved labelling.” The company notes that, armed with the same data, the US Food and Drug Administration last year revised the Adderall XR label, clarifying that the drug generally should not be used in children or adults with structural cardiac abnormalities. However, regulators seem to be taking a tougher stance on drug safety in the wake of Merck & Co’s withdrawal of its top-selling osteoarthritis and acute pain medicine, Vioxx (rofecoxib) [[01/10/04a]].

Adderall XR won Canadian approval early last year [[04/02/04d]], and Shire notes that around 11,000 patients are currently prescribed the drug in this market. Canadian sales of Adderall XR contributed some $10 million dollars to Shire’s annual revenue in its first year on the market.