The British Journal of Psychiatry 139: 400-404 (1981)
© 1981 The Royal College of Psychiatrists
Neuroendocrine tests during treatment with neuroleptic drugs I. Plasma prolactin response to haloperidol challenge
T Kolakowska, L Braddock, D Wiles, M Franklin and M Gelder
The plasma prolactin (PRL) response to haloperidol 2 or 4 mg i.m. was
studied in 18 schizophrenic men during their routine treatment with
neuroleptic drugs. A substantial rise of the PRL level above the treatment
baseline occurred in all but four of the 20 tests showing that the PRL
elevation induced by treatment was not maximal. The challenge was
ineffective only in patients receiving very high daily doses of medication.
The increment was inversely correlated to the daily dose of medication but
unrelated to plasma haloperidol concentrations during the test. Chronic
schizophrenics who were receiving long term treatment and had low basal PRL
levels did not show tolerance to the prolactin stimulating effect of
haloperidol. That prolactin rose during the test in patients who had
improved during their current treatment indicates that the degree of
dopamine receptor blockade required for therapeutic effects is below that
which produces a maximal PRL response.