Pharmacokinetics and therapeutic efficacy of haloperidol decanoate after loading dose administration

For this open study, we selected 21 chronic psychotic female in-patients (16 of them schizophrenics) who were being maintained on oral neuroleptics. After a wash-out period, they were treated by intramuscular depot injections of haloperidol decanoate, once a month for four months. The dose was calculated from the previous oral dosage, and the amount of the first injection was double that of the three following injections. Relatively stable plasma levels of haloperidol were achieved with the first injection, and corresponded to those observed with oral medication. A very significant correlation was found between plasma level and the dose administered, but not between plasma level and therapeutic effect. The clinical condition of about two-thirds of the patients remained unchanged or improved, compared with the period of oral treatment. During the first two months of treatment, there was more rigidity and tremor, but from the third month, the extrapyramidal symptoms were less pronounced than during the period of oral neuroleptics.