Haloperidol

Haloperidol

Synonym: haldol
Chemical name: 4-[4-(p-chlorophenyl)-4-hydroxypiperidol]-4’-fluorobutyrophenone
CAS: 52-86-8
MF: C21H23ClFNO2
FW: 375.9
Solubility: insoluble in water; soluble in ethanol and DMSO.
Major uses
Haloperidol is a neuroleptic drug for the treatment of psychotic disorders (e.g.
schizophrenia, mania, psychopathy etc.). It is also a widely used tranquilizer (e.g. for
treatment of behavioral problems in hyperactive children) [1]. Haloperidol may be
used as a drug of abuse [2].
Human toxicity
Most common major signs of acute intoxication at a massive overdose are the central
nervous system (CNS) depression, somnolence, coma, respiratory depression, cardiac
dysrhythmia and hypotension.
The recommended daily dose for patients with moderate symptoms is 1 to 6 mg, and
for patients with severe symptoms, 6 to 15 mg. Maximum tolerated doses are between
300 and 1000 mg [2].
In adults, ingestion of 300 mg or more have experienced life-threatening symptoms.
Some individuals have had fatal reactions to even therapeutic doses of haloperidol. At
the same time, it happened that adults survived overdoses as large as 1000 mg [2].
Therapeutic blood plasma concentrations are in the range of 0.005-0.02 mg/l [3]. In
patients who respond to haloperidol, a serum concentration of at least 0.005 mg/l is
advisable to ensure a positive response. Side effects increased in incidence with
plasma concentrations greater than 0.006 mg/l, at 12 to 14 h after the final
administration [4]. The toxic plasma/serum level of haloperidol was reported to be
0.005-0.05 mg/l [5].
The lethal blood levels have not been definitively established; however, in one fatal
case with suicidal overdose, post mortem heart blood concentration of haloperidol
was 1.9 mg/l (5 μM)); in second fatal case, which was believed to be a natural cardiac
death, heart blood concentration of haloperidol was 0.6 mg/l (1.6 μM) [6].
Kinetic data [4]
Absorption: haloperidol is well absorbed from the gastrointestinal tract.
Volume of distribution (Vd): 20 l/kg.
Blood protein bindning: 90-94%.
Peak serum concentration levels are attained 0.5 to 4 h after an oral dose.

Elimination: clearance occurs exclusively by hepatic metabolism.

The elimination half-life ranges from 13 to 35 h.
Metabolism and excretion
Haloperidol is mainly metabolized by the liver, where it undergoes cytochrome P450-
catalyzed oxidative cleavage of hydrocarbon chain, forming inactive fluorophenyl and
piperidine metabolites. An additional metabolic pathway involves reduction of the
keto group on the side chain to an alcohol, forming a compound known as reduced
haloperidol. The latter has about 25% of the antipsychotic activity of the parent drug
(reviewed in [6]).
Other identified metabolites include 4-fluorobenzol-propionic acid and 4-fluoro-
phenylaceturic acid [2].
Excretion: Renal excretion is negligible, with less than 1% of an administered dose
excreted in the urine.
Pharmacological and toxicological mechanisms
Similar to the other neuroleptics, haloperidol is a dopamine receptor antagonist: it
blocks D-2 dopamine receptors in the brain. Thus, the antipsychotic activity of this
anticholinergic drug is closely associated with its ability to block the action of
dopamine [1, 2].
The toxic effect of haloperidol is related to blocking of dopamine receptors in the
CNS; however, the knowledge of exact mechanisms is still meager [1].
Target organs: CNS, heart, liver [1].
References
1. Haddad, L.M., Winchester, J.F. (1990) Clinical Management of Poisoning and
Drug Overdose. 2nd ed., pp. 780-793. W.B. Saunders Company.
2. Poisindex, Thomson Micromedex (2005).
3. Cheng, V.A., Paalzow, L.K., Bondesson, U., Ekblom, B., Eriksson, K., Eriksson,
S.O., Lindberg, A., Lindström, L. (1987) Pharmacokinetics of haloperidol in
psychotic patients. Psychopharmacology 91, 410-414.
4. Ellenhorn, M.J., Schonwald, S., Ordog, G., Wasserberger, J. (1997) Ellenhorn’s
Medical Toxicology: Diagnosis and Treatment of Human Poisoning, 2nd ed., pp. 674-
675. Williams & Wilkins.
5. Winek, C.L. (1994) Drug and chemical blood-level data. Winek’s Toxicological
Annual, Pittsburgh. Allegheny County Department Laboratories.
6. Levine, B.S., Wu, S.C., Goldberger, B.A., Caplan, Y.H. (1991) Two fatalities
involving haloperidol. J Anal Toxicol 15, 282-284.
Written by Ada Kolman, December 2005; revised March 2007

Source: http://www.acutetox.eu/pdf_human_short/62-Haloperidol%20revised.pdf