Haloperidol chemical structureImage:Haloperidol_decanoate_chemical_structure.png
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Haloperidol

Haloperidol (sold as Aloperidin®, Bioperidolo®, Brotopon®, Dozic®, Einalon S®, Eukystol®, Haldol®, Halosten®, Keselan®, Linton®, Peluces®, Serenace®, Serenase®, Sigaperidol®) is a conventional butyrophenone antipsychotic drug. It was developed in 1957 by the Belgian company Janssen Pharmaceutica and submitted to first clinical trials in Belgium in the same year. After being rejected by U.S. company Searle due to side effects, it was later marketed in the U.S. more...

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by McNeil Laboratories.

Chemistry

Haloperidol is an odourless white to yellow crystalline powder. Its chemical name is 4--4'-fluorobutyrophenone and its empirical formula is C21H23ClFNO2

Pharmacology

Haloperidol is a neuroleptic, a butyrophenon. Due to its strong central antidopaminergic action, it is classified as a highly potent neuroleptic. It is approximately 50 times more potent than chlorpromazine on a weight basis (50mg chlorpromazine are equivalent to 1mg haloperidol). Haloperidol possesses a strong activity against delusions and hallucinations, most likely due to an effective dopaminergic receptor blockage in the mesocortex and the limbic system of the brain. Too, it blocks the dopaminergic action in the nigrostriatal pathways, which is the probable reason for the high frequency of extrapyramidal-motoric side-effects (dystonias, akathisia, pseudoparkinsonism). It has minor antihistaminic and anticholinergic properties, therefore cardiovascular and anticholinergic side-effects such as hypotension, dry mouth, constipation, etc., are seen quite infrequently, compared to less potent neuroleptics such as chlorpromazine. Haloperidol also has sedative properties and displays a strong action against psychomotor agitation, due to a specific action in the limbic system. It therefore is an effective treatment for mania and states of agitation. Additionally, it can be given as an adjuvant in the therapy of severe chronic pain.

The peripheral antidopaminergic effects of haloperidol account for its strong antiemetic activity. There, it acts at the CTZ (Chemical Trigger Zone). Haloperidol is useful to treat severe forms of nausea/emesis such as those resulting from chemotherapy. The peripheral effects lead also to a relaxation of the gastric sphincter muscle and an increased release of the hormone prolactin, with the possible emergence of breast enlargement and secretion of milk (lactation) in both sexes.

Pharmacokinetics

Oral dosing

Haloperidol is well absorbed after oral dosing. There is a first pass metabolism leading to a reduced oral biovailability of the drug (60 to 70%). Peak plasma-levels are observed after 3 to 6 hours.

I.m. injections

The drug is well and rapidly absorbed and has a high bioavailability. Plasma-levels reach their maximum within 20 minutes after injection.

I.v. injections

The bioavailability is 100% and the very rapid onset of action is seen within about ten minutes. The duration of action is 3 to 6 hours. If haloperidol is given as slow i.v.-infusion, the onset of action is retarded, but the duration prolonged compared to i.v.-injection.

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Use of Haloperidol in Alzheimer's Disease
From American Family Physician, 4/1/99

Nearly one half of patients with Alzheimer's disease may experience psychomotor agitation. Untreated psychosis and disruptive behaviors are distressing to both patients and caregivers, and may force institutionalization. A meta-analysis has suggested the moderate superiority of neuroleptic agents over placebo in the treatment of psychosis and agitation in patients with dementia. However, neuroleptics are poorly tolerated by patients with Alzheimer's disease. Devanand and associates performed a randomized, double-blind, placebo-controlled trial of haloperidol and placebo to determine the optimal dosage of haloperidol to treat patients who have Alzheimer's disease with psychosis and disruptive behaviors.

During the six-week trial, 71 outpatients with Alzheimer's disease were randomized to receive a "standard" dosage of haloperidol (2 to 3 mg per day), a "low" dosage of haloperidol (0.50 to 0.75 mg per day), or placebo. The standard dosage range was toward the high end of dosages used clinically but was also below the dosage of 5 mg per day that often results in severe extrapyramidal signs. In a subsequent six-week cross-over phase, patients who were taking haloperidol were switched to placebo, and those who were taking placebo were switched to haloperidol.

Analyses indicated that in all measures of efficacy, therapeutic effects were greater with the standard dosage of haloperidol (55 to 60 percent rate of response) than with either the low dosage of haloperidol (25 to 35 percent rate of response) or placebo (25 to 30 percent rate of response). Significant differences were seen in patients taking the standard dosage in the reduction of psychosis and psychomotor agitation, but not in physical aggression and hostility/suspiciousness.

Extrapyramidal signs tended to be greater with the standard dosage of haloperidol than with the low dosage or placebo. Twenty percent of the patients in the group taking the standard dosage developed moderate to severe extrapyramidal signs.

Forty-nine patients entered the cross-over phase. Patients who switched from placebo to standard dosage therapy showed nonsignificant superiority to the low dosage group in physical aggression, psychomotor agitation, hostility/suspiciousness and psychosis. The patients first treated with haloperidol who switched to treatment with placebo demonstrated a partial reversal of the improvement that was noted in the acute phase. Patients who switched to placebo after six weeks of standard-dose haloperidol displayed worsening symptoms, indicating that a longer period of treatment is necessary before discontinuation of medication should be attempted.

The authors conclude that the use of 2 to 3 mg per day of haloperidol leads to an acceptable trade-off between efficacy and side effects for psychotic or agitated patients with Alzheimer's disease, except in those who develop moderate to severe extrapyramidal signs. Dosages below 1 mg per day are ineffective. There appears to be a narrow therapeutic window for patients with Alzheimer's disease who are treated with haloperidol that may also apply to other neuroleptic agents. Since many patients who received 2 to 3 mg per day of haloperidol developed moderate to severe extrapyramidal signs, a starting dosage of 1 mg per day with gradual upward dosage adjustments is recommended. Close monitoring is needed to ensure the efficacy and safety of the treatment.

Barbara Apgar, M.D.., M.S.

Devanand DP, et al. A randomized, placebo-controlled dose-comparison trial of haloperidol for psychosis and disruptive behaviors in Alzheimer's disease. Am J Psychiatry November 1998;155:1512-20.

COPYRIGHT 1999 American Academy of Family Physicians
COPYRIGHT 2000 Gale Group

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