Withdrawal from clozapine: the "rebound phenomenon".

Clozapine is an "atypical" antipsychotic agent for treating previously resistant schizophrenic patients. Its main advantages over "typical" neuroleptics are low incidence of extrapyramidal side effects and its capacity to induce therapeutic response in previously treated refractory patients. However, withdrawal from clozapine has been observed to lead to "atypical" clinical characteristics or a "rebound phenomenon," manifested in two interwoven clinical forms: (1) psychotic exacerbation, and (2) cholinergic rebound. The underlying pathophysiological mechanism of this phenomenon is postulated to be a result of cholinergic supersensitivity. In this paper, the "rebound phenomenon" will be discussed and exemplified by three case histories in which abrupt cessation of clozapine led to serious deterioration and psychotic exacerbation, and one case in which gradual titration from the drug was employed in order to preempt this hazardous occurrence.