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Quetiapine (Seroquel) is an atypical antipsychotic drug indicated for the management of the symptoms of schizophrenia and the acute management of manic episodes associated with bipolar disorder.1 In Canada, quetiapine has been marketed since December 1997.
From Dec. 1, 1997, to Oct. 31, 2006, Health Canada received 615 domestic reports of adverse reactions (ARs) suspected of being associated with the use of quetiapine. Nine reports involved cases of pancreatitis and 11 involved cases of thrombocytopenia. Neither of these ARs is mentioned in the Canadian product monograph.1
Pancreatitis
The 9 reported cases of pancreatitis involved patients aged 24-71 years (median 32 years). One patient experienced severe hemorrhagic pancreatitis, and another had necrotizing pancreatitis. In one case, the patient experienced pancreatitis on 2 occasions while taking quetiapine. In 5 cases, quetiapine was the only suspect drug; in the other 4 cases, reported cosuspect drugs included medications that, like quetiapine, have been associated with pancreatitis: clozapine, divalproex sodium, fenofibrate and minocycline.2,3
Acute pancreatitis typically presents as an acute inflammation of the pancreas that may or may not involve the surrounding tissues.2 Gallstones and heavy alcohol use are the most common causes.2 Drug-induced pancreatitis is less common, with an incidence of 2%-5% of reported cases of acute pancreatitis in the general population.2 Of the 9 cases reported to Health Canada, concomitant alcohol use was reported in 1 case. The severity of drug-induced pancreatitis is variable; the majority of patients recover without any long-term morbidity, but 5%-15% of patients experience life-threatening complications.4 People at risk of drug-induced pancreatitis include elderly patients taking multiple medications, patients who are HIV positive, patients who have cancer and patients receiving immunomodulatory agents.5
Thrombocytopenia
The 11 reported cases of thrombocytopenia involved patients aged 28-84 years (median 63.5 years). In 6 cases, quetiapine was the only suspect drug. In 1 of these 6 cases, the patient was rechallenged 1 month after the drug was stopped; the thrombocytopenia recurred 3 months after the quetiapine was reintroduced. In 5 cases, reported co-suspect drugs included medications that, like quetiapine, have been associated with thrombocytopenia: citalopram, clozapine, olanzapine, pantoprazole, rofecoxib and zuclopenthixol.6-12
Thrombocytopenia is usually defined as a platelet count of less than 150...