Clozapine in the treatment of tremor in Parkinson's disease.

Tremor at rest is a classic symptom of Parkinson's disease that causes significant disability and distress for the patient and is generally only weakly responsive to conventional treatment, like anticholinergic and dopaminergic medication. This study describes the treatment with Clozapine in patients with Parkinson's disease, who despite optimal antiparkinson medical therapy still have a major disabling tremor at rest. Clozapine is an "atypical" neuroleptic agent, producing fewer extra pyramidal side effects common to conventional antipsychotic drugs. Clozapine, however, has as its most serious complication agranulocytosis, and hence all patients taking Clozapine must undergo blood tests at least several times a month. Under these frequent blood monitoring conditions, in this study Clozapine produced a substantial alleviation of parkinsonian tremor in 17 of 23 patients (73%). The beneficial response was reached with a relative low dose of Clozapine (18 mg./day), while previous antiparkinson medication was kept unchanged. The improvement of tremor at rest was noticeable generally within 2 weeks of beginning Clozapine therapy. No tolerance to the antitremor efficacy of Clozapine was seen during study-period of at least 6 months. Leucopenia developed in one patient, other major adverse events were hypersalivation and day-time drowsiness. These findings confirm the substantial antitremor efficacy of Clozapine in Parkinson's disease.