The fall-out from the decision by Canadian drug regulators to suspend sales of Shire’s attention deficit hyperactivity disorder medication, Adderall XR (amphetamine salts extended-release), over concerns it had been linked to the sudden death of 20 patients [[10/02/05a]], shows little sign of abating.

Angry with Health Canada’s request to withdraw the drug, Shire has been vigorous in its defence of the safety of its treatment, a stance that seemed to be backed wholeheartedly by the US Food and Drug Administration, which said that it does not feel that any immediate changes are warranted in the labelling or approved use of Adderall XR. However, just a couple of days after that announcement, the FDA was reportedly thinking of asking Shire to consider conducting further epidemiological studies to determine risk. Citing “a top official at the agency”, Reuters noted that the FDA could conduct trials to determine whether the risks are higher in children than the general population. This would probably cause some consternation at Shire given that the data presented to the Canadian authorities was also seen by the FDA last year when it revised the Adderall XR label, clarifying that the drug should not be used in people with structural cardiac abnormalities.

As if this was not enough, the New York Times reported claims from US senator Charles Grassley that a whistleblower at the FDA told him that the agency asked Health Canada officials not to withdraw Adderall XR from the market, because it could not handle another “drug safety crisis”.

The director general of the therapeutic products directorate at Health Canada, Dr Robert Peterson, reportedly denied the allegation, but Senator Grassley has written to the FDA demanding that it discloses information about any discussions it may have held with Canadian officials about Adderall. The senator has been investigating the FDA’s activities for over a year.