Absolute Agranulocytosis After 9 Weeks of Clozapine 25 mg Daily

Clozapine has been shown to be an effective and well-tolerated treatment for Parkinson disease (PD) psychosis as well as for refractory tremor in PD. Doses used are generally less than one tenth those used in treating schizophrenia. While the risk of leukopenia and agranulocytosis are reported to be independent of dose, that belief is based on the use of doses used in refractory schizophrenia. There are no published data on the risk of agranulocytosis in patients taking extremely low doses of clozapine.

This 87-year-old man with diabetes and PD experienced a granulocyte count drop from normal, 3900, at dose initiation, to 0, at the ninth week of treatment taking clozapine 12.5 mg twice daily for refractory tremor. He recovered without developing an infection.

This is the first known reported case of agranulocytosis due to clozapine used at an extremely low dose. This report underscores the importance of blood monitoring, even at extremely low doses, although the exact risk remains unknown.