Evolution of plasma homovanillic acid (HVA) in chronic schizophrenic patients treated with haloperidol

In a 4‐week study of 14 drug‐free schizophrenic patients (according to DSM‐III‐R), free and conjugated fractions of plasma homovanillic acid (pHVA) were repeatedly measured. Free HVA levels decreased during the first 2 h of haloperidol intake (P<0.03). Conjugated HVA levels slowly decreased during the following weeks (P<0.05), while free HVA levels remained stable. After 4 weeks, free HVA levels remained unchanged 2 h after morning haloperidol intake, but conjugated HVA levels tended to increase. In haloperidol responders, at baseline the free/total HVA ratio was significantly higher than that in non‐responders (P<0.01). Tolerant patients, i.e. those whose post‐treatment free HVA levels decreased below pre‐treatment levels, were not found to respond better to haloperidol than non‐tolerant patients. The balance between free and conjugated pHVA may be a better reflection of the action of haloperidol than free pHVA levels and it may be of prognostic value in terms of drug response.