Human platelet function as a model for investigating the clinical efficacy of chlorpromazine.

1 Enhancement of platelet aggregation response (PAR) to 5-hydroxytryptamine (5-HT) in some schizophrenic patients receiving chlorpromazine (CPZ) may provide a biological index for the efficacy of this drug. 2 In a double-blind study 33 schizophrenic patients hospitalized following their first psychotic breakdown were followed up clinically with concurrent assessment of their PAR to 5-HT. The patients followed a standardized treatment schedule with (CPZ) as the sole antipsychotic medication. 3 Twelve patients (Group A) developed an enhanced biphasic 5-HT PAR, within 2-3 weeks and improved clinically by the sixth week. In most cases, the appearance of the enhanced biphasic PAR preceded clinical improvement. Twenty-one patients (Group B) did not have enhanced biphasic PAR to 5-HT by the sixteenth week of treatment. However, twelve subjects from this group showed clinical response to CPZ by the end of this period, while the remaining patients did not improve. 4 The enhanced PAR to 5-HT in Group A discriminated best between good and bad outcome cases when Feighner's research diagnostic criteria were used. We could not confirm the previous reports of platelet aggregation response to dopamine in pre- or post-chlorpromazine treatment.