Neuroleptic drug-induced coagulopathy: mechanism of reaction and duration of effect.

Patients (N = 32) with documented phenothiazine-induced reductions in platelet levels were evaluated after drug substitution with haloperidol; 28 (88%) patients had normal platelet levels after 1 year of treatment with haloperidol. Coagulation studies indicated that activated partial thromboplastin time (APTT) elevations were more common in patients previously treated with chlorpromazine than in those previously treated with fluphenazine. There was no relationship between attenuation of reduced platelet levels and reduced APTT ratios. This preliminary study indicates that there may be two mechanisms of phenothiazine-induced coagulopathy.