The effect of thioridazine on prolactin levels in acutely schizophrenic patients: challenge-dose and steady-state levels.

Prolactin (PRL) levels in unmedicated male patients with acute schizophrenia were within normal range at baseline, increased five fold after a challenge dose of thioridazine, did not significantly increase further after therapeutic dosages, and remained elevated for the duration of treatment. The rise in PRL levels was significantly correlated with the steady-state plasma levels of thioridazine and/or mesoridazine. Baseline and challenge-dose PRL levels did not correlate with severity of symptoms as measured by the Brief Psychiatric Rating Scale, or predict response to thioridazine. Overall, there was a trend for the drug and PRL levels to increase very quickly and remain elevated while the clinical response was gradual over the four-week period. clinically, it may be useful monitoring PRL levels, since the therapeutic dosage should usually be above the dosage required to produce maximal PRL levels.