Neuroleptic serum levels measured by radioreceptor assay in patients receiving intramuscular depot neuroleptics. Some preliminary findings.

Twenty-six chronic schizophrenic patients on well established depot neuroleptic regimes with stable doses (16 on fluphenazine decanoate, ten on flupenthixol decanoate) had serum neuroleptic levels measured by a radioreceptor assay (RRA) method. The assay was sufficiently sensitive to measure serum levels in all cases, with acceptable levels of inter-assay variation. Blood level measurements were repeated on two occasions, at the same time interval from the last injection, in 18 patients (11 on fluphenazine decanoate, seven on flupenthixol decanoate) and remained reasonably stable in most cases, although others showed a wider variation. Despite a wide range of doses (X 32 fluphenazine decanoate, X 21 flupenthixol decanoate) the serum levels fell in a remarkably narrow range (X 4, X 6). There was a significant correlation between dose and blood level for flupenthixol decanoate, but not for fluphenazine decanoate.