Possible serotonin syndrome associated with clomipramine after withdrawal of clozapine

To report on the possible development of serotonin syndrome in a patient receiving clomipramine after clozapine was withdrawn from the treatment regimen.

A 44-year-old white man with a 23-year history of undifferentiated schizophrenia and obsessive-compulsive behavior had been treated with clozapine and clomipramine for several years. He tolerated both agents together well, with the exception of experiencing chronic constipation. Clomipramine was tapered and reduced to 50 mg over a period of 10 days. A worsening of ritualistic behavior was noted, and the clomipramine dosage was increased to 150 mg/d over 14 days. Simultaneously with the clomipramine dosage increase, clozapine was tapered and stopped ever a period of 19 days. The day after clozapine was stopped, while he was still receiving clomipramine 150 mg/d, he began behaving oddly, started sweating profusely, shivering, and became tremulous, agitated, and confused. He was diagnosed with possible serotonin syndrome; his symptoms resolved after clomipramine was stopped but before clozapine was restarted eight days later.

There are similarities in symptoms between serotonin syndrome and clozapine withdrawal. This article discusses the reasons why this case may represent serotonin syndrome rather than clozapine withdrawal and the possible pharmacologic mechanisms involved.

Clinicians should be aware that removing a serotonin-2a (S-HT2a) antagonist 1mm a treatment regimen including an agent that increases serotonin in the synaptic cleft may worsen clozapine withdrawal or potentially result in serious adverse drug reactions, such as serotonin syndrome.