[Clozapine withdrawal. A review]

The article describes the symptoms of withdrawal of clozapine and their possible causes as well as research on switching from clozapine to another antipsychotic drug. A computerised search was conducted using MEDLINE (1966-1997) to retrieve reports of clozapine withdrawal. Fifteen case reports and sixteen withdrawal studies (only one of them double-blind and two single-blind) were identified. Clozapine multi-receptors profile seems to be responsible for withdrawal symptoms--several specific mechanisms are suggested: cholinergic supersensitivity, dopaminergic supersensivity, special role of D4 receptors, possibilities of serotonergic, noradrenergic and GABA-ergic involvement. Risk of relapse after withdrawal of clozapine seems to be greater than after withdrawal of classical neuroleptics. Some patients might become de novo neuroleptic resistant for at least several weeks after withdrawal. Therefore, clozapine should be stopped only due to strong clinical indications, and if only possible, the withdrawal should be slow (50 mg/week). To prevent relapse of psychosis some experts advocate starting new antipsychotic drugs in therapeutic dosage before withdrawal of clozapine is completed. In case of emergency, when clozapine (high dosage) must be withdrawn immediately, patient must be hospitalised and cholinergics might be considered to prevent, cholinergic rebound". There are no established guidelines which antipsychotic to choose after withdrawal of clozapine. In general, classical antipsychotics are ineffective. Thioridazine is suggested because of its prominent anticholinergic activity, but there is no clinical evidence of advantage of this treatment in comparison to classical drugs. Risperidon and especially olanzapine are promising possibilities, but initial data are disappointing. Benzamides might be another possibility but clinical data are scarce. These important issues require further studies.