Lack of tolerance to long-term neuroleptic treatment in dopamine tuberoinfundibular system

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Abstract
The plasma prolactin (PRL) levels of 35 chronic schizophrenic patients undergoing long‐term maintenance treatment with neuroleptic drugs were measured before and after either neuroleptic withdrawal or a switch to a fixed dose of chlorpromazine 900 mg/ day. In both men and women there tended to be a significant correlation between the initial log plasma PRL level while on neuroleptic maintenance treatment and the dosage received converted to chlorpromazine equivalents. Neuroleptic withdrawal in each of 19 cases was followed by a decline in PRL plasma levels. Switching to chlorpromazine 900 mg/day (16 cases) produced either increases or decreases in PRL plasma levels that were significantly correlated with the change in neuroleptic dosage converted to chlorpromazine equivalents. Thus there was no evidence of tolerance to the PRL‐elevating effect of neuroleptics in these patients who had been treated for many years with neuroleptics.