Within-individual variation in steady state plasma levels of different neuroleptics and prolactin.

Eleven male chronic schizophrenics were given, serially, oral pimozide, fluphenazine, and flupenthixol; the two latter were also given intramuscularly as decanoates in oil. Oral haloperidol was given before and after each drug. Analysis of variance of steady state plasma levels of the different neuroleptics showed considerable within-individual variation in such levels, probably due to differences in absorption and metabolism and between routes of administration. The findings suggest that if a patient fails to respond to one neuroleptic, there may be good pharmacokinetic reasons for switching him to another belonging to a different group, or for giving the same neuroleptic by a different route of administration. The study also showed that previous administration of one neurololeptic may influence the steady state level of another. The various neuroleptics produced different effects on plasma prolactin levels.