Determination of plasma haloperidol concentrations by radioreceptor assay in schizophrenia: clinical utility.

1. Haloperidol concentrations were determined by radioreceptor assay (RRA) and prolactin concentrations were measured in 20 patients diagnosed as schizophrenia (DSM-III). 2. The patients were treated with a fixed dose of haloperidol for 21 days. 3. Our results suggest the existence of a curvilinear relationship, in the form of an inverted U, between stable haloperidol levels and clinical improvement assessed by total BPRS score. 4. We also found a curvilinear relationship between the improvement observed in positive symptoms and state steady levels. 5. No relationship was seen between improvement in negative symptoms and state steady levels. 6. An interval of optimal haloperidol concentration was found: 8.1 ng/ml to 19.6 ng/ml. 7. No relation was found between the dose of haloperidol administered and plasmatic concentration, nor between haloperidol and prolactin levels. 8. Our findings suggest that haloperidol concentrations determined by RRA have clinical utility as predictors of response in schizophrenia.