Plasma homovanillic acid in schizophrenics: supportive evidence for the two-subtype hypothesis.

Plasma levels of homovanillic acid (pHVA), a major metabolite of dopamine (DA), were measured in a group of 51 schizophrenic inpatients before and during 6 weeks of neuroleptic treatment. Steady-state plasma drug concentrations were monitored in parallel with pHVA. Good responders (n = 22) had higher pretreatment pHVA levels as compared to poor responders (n = 22). Differential pHVA changes during neuroleptic treatment were also found between each group. The two groups did not differ significantly in terms of age, duration of illness, severity of presenting symptoms, neuroleptic, dose, or plasma drug concentration. Two hypothetical subtypes in the group of schizophrenics were proposed.