Antiemetic effect of haloperidol in the dog as related to plasma level and dose

Effect of haloperidol on dopamine-induced increase in renal blood flow

Increasing renal blood flow (RBF) by the administration of low-dose dopamine is one mechanism to increase urine output in oliguric patients. This response is mediated in part by stimulation of dopaminergic receptors in the kidney, which could be attenuated by the dopamine blocker haloperidol. We evaluated this interaction by administering both drugs in clinically used doses to six anesthetized mongrel dogs. A dopamine regimen of 2.5 micrograms/kg/min significantly increased RBF along with cardiac output and stroke volume. Simultaneous administration of haloperidol 50 micrograms/kg iv did not influence the ability of low-dose dopamine to increase RBF. Although haloperidol is an antagonist of dopaminergic receptors, the increase in RBF associated with low-dose dopamine is maintained when intravenous haloperidol is concurrently administered to dogs.

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.

Reduced haloperidol in the post-mortem brains of haloperidol-treated patients

We measured the concentrations of haloperidol and its reduced alcohol metabolite in human post-mortem tissues with high-performance/liquid chromatography using electrochemical detection. Both haloperidol and reduced haloperidol were detected and quantified in the occipital cortex of nine schizophrenic patients with a history of haloperidol treatment, but not in six samples from nontreated subjects. Reduced haloperidol concentrations were below the detection limit of the assay in several tissues of rats and mice even after 10 days of haloperidol treatment. The results suggest that reduced haloperidol is present in the brains of haloperidol-treated patients at slightly higher concentrations than haloperidol itself. Further studies are warranted to establish the possible biological importance of this haloperidol metabolite.

The dissociation rate of unlabelled dopamine antagonists and agonists from the dopamine-D2 receptor, application of an original filter method

A filtration technique was developed to measure the dissociation rate of unlabelled drugs from membrane receptors. Receptor preparations saturated with unlabelled drug were adsorbed to glass fibre filters positioned on a filtration apparatus. Dissociation of the drug from the receptor sites was achieved by repeatedly applying small buffer samples on the filter, this was followed by short incubation on the filter with a [3H]ligand. Rat striatal membrane preparations adsorbed on filters retained the same dopamine-D2 receptor binding properties as the tissue in aqueous suspension. Stereospecific [3H]haloperidol binding was maximal with 20 mg tissue per filter and 5 min incubation, KD = 2.8 nM and Bmax = 24 fmoles/mg tissue was found. The dissociation from the dopamine-D2 receptor for 18 dopamine antagonists and 3 agonists followed first order reaction kinetics. Half-lifes of dissociation ranged from 3.5 min for azaperone to 233 min for metitepine. There was no strict relationship between dissociation half-life and apparent equilibrium binding affinity or lipophilicity of the drugs. Half-life of receptor dissociation appeared neither to be a primary determining factor in the duration of pharmacological action of the drugs. The importance of the drug receptor dissociation rate for binding experiments in vitro as well as for chronic drug treatment is discussed.