The manufacturer of mesoridazine besylate (Serentil®) has advised doctors and pharmacists of important prescribing information changes to the 25 mg and 50 mg tablets. Mesoridazine besylate has been shown to prolong the QTc interval in a dose-related manner and drugs with this potential have been associated with torsade de pointes and sudden death. The following major modifications should be implemented immediately:

• Mesoridazine besylate is now indicated only for schizophrenic patients who fail to show an acceptable response to other antipsychotic drugs. Efficacy of mesoridazine besylate in treatment refractory schizophrenic patients is unknown.

• Mesoridazine besylate is contraindicated with other drugs known to prolong the QTc interval, in patients with congenital long QT syndrome or a history of cardiac arrhythmias.

• Patients considered for treatment with mesoridazine besylate should have a baseline ECG performed and serum potassium levels measured.

Patients currently being treated with mesoridazine besylate should be fully informed of these information changes and switching to a different antipsychotic agent should be considered. Thioridazine, a metabolic precursor of mesoridazine also appears to have the capacity to prolong the QTc interval.

Reference: Communication from Novartis Pharmaceuticals Canada Inc., Canada, dated 22 September 2000.