Thrombocytopenia with quetiapine: two case reports, one with positive rechallenge.

Antipsychotic-induced thrombocytopenia is generally rare, but seems to occur more frequently with quetiapine. Accordingly, the relative risk of thrombocytopenia can be described as very rare with loxapine and clozapine (o 0.01%), uncommon with risperidone (X 0.1%, o 1%), but very common with quetiapine (X 10%). However, very few cases are reported in the literature, with one published case of idiopathic thrombocytopenic purpura, and it remains unclear whether rechallenge may be considered. Patient no. 1 was a 78-year-old male hospitalized for depressive syndrome and treated with mirtazapine 45 mg/day, valpromide 1,000 mg/day, and oxazepam 30 mg/day. Quetiapine was added at 50 mg/day, while mirtazapine was reduced to 30 mg/day. Laboratory tests carried out the following day and 5 days after the start of treatment with quetiapine revealed platelet counts of 100,000/mm and 56,000/mm respectively. Two further measurements were obtained, 8 days and 28 days after discontinuing treatment with quetiapine, showing higher platelet levels of 85,000/mm and 120,000/mm respectively. Patient no. 2 was a 72-year-old female hospitalized for personality disorders with hallucinations and treated with aripiprazole 15 mg/day, clonazepam 0.6 mg/day, valproic acid 1,500 mg/day, furosemide 40 mg/day, lisinopril 20 mg/day, nebivolol 5 mg/day, and amlodipine 10 mg/day. During her hospitalization, aripiprazole was stopped and quetiapine 50 mg/day was introduced. Tests performed 3 months after initiating treatment with quetiapine were notable for a platelet count of 107,000/mm. Six days later, a second test was carried out, and the platelet count was down to 95,000/mm. Treatment with quetiapine was suspended for 3 days, following which the platelet count went back up to 120,000/mm. The psychiatrist reintroduced quetiapine and scheduled a control platelet test 5 days later, which showed a decrease to 84,000/mm. In view of this positive rechallenge, quetiapine was discontinued definitively. Fifteen days after quetiapine discontinuation, the platelet count was 123,000/mm. In both situations, no other clinical or iatrogenic parameter seemed to account for the onset of thrombocytopenia. To our knowledge, the second patient described herein is the first case of quetiapine-induced thrombocytopenia with positive rechallenge to be in the literature.