Haloperidol

Medical uses

Haloperidol is used in the control of the symptoms of:

Schizophrenia

Acute psychosis, such as drug-induced psychosis caused by LSD, psilocybin, amphetamines, ketamine, and phencyclidine, and psychosis associated with high fever or metabolic disease

Hyperactivity, aggression

Hyperactive delirium (to control the agitation component of delirium)

Otherwise uncontrollable, severe behavioral disorders in children and adolescents

Agitation and confusion associated with cerebral sclerosis

Adjunctive treatment of alcohol and opioid withdrawal

Treatment of severe nausea and emesis in postoperative and palliative care, especially for palliating adverse effects of radiation therapy and chemotherapy in oncology

Treatment of neurological disorders, such as tic disorders such as Tourette syndrome, and chorea

Therapeutic trial in personality disorders, such as borderline personality disorder

Treatment of intractable hiccups

Alcohol-induced psychosis

Hallucinations in alcohol withdrawal

Haloperidol was considered indispensable for treating psychiatric emergency situations, although the newer atypical drugs have gained greater role in a number of situations as outlined in a series of consensus reviews published between 2001 and 2005.

A multiple-year study suggested this drug and other neuroleptic antipsychotic drugs commonly given to Alzheimer's patients with mild behavioural problems often make their condition worse and its withdrawal was even beneficial for some cognitive and functional measures.

Pregnancy and lactation

Data from animal experiments indicate haloperidol is not teratogenic, but is embryotoxic in high doses. In humans, no controlled studies exist. Reports in pregnant women revealed possible damage to the fetus, although most of the women were exposed to multiple drugs during pregnancy. In addition, reports indicate neonates exposed to antipsychotic drugs are at risk for extrapyramidal and/or withdrawal symptoms following delivery, such as agitation, hypertonia, hypotonia, tremor, somnolence, respiratory distress, and feeding disorder. Following accepted general principles, haloperidol should be given during pregnancy only if the benefit to the mother clearly outweighs the potential fetal risk.

Haloperidol, when given to lactating women, is found in significant amounts in their milk. Breastfed children sometimes show extrapyramidal symptoms. If the use of haloperidol during lactation seems indicated, the benefit for the mother should clearly outweigh the risk for the child, or breastfeeding should be stopped.

Other considerations

During long-term treatment of chronic psychiatric disorders, the daily dose should be reduced to the lowest level needed for maintenance of remission. Sometimes, it may be indicated to terminate haloperidol treatment gradually. In addition, during long-term use, routine monitoring including measurement of BMI, blood pressure, fasting blood sugar, and lipids, is recommended due to the risk of side effects.

Other forms of therapy (psychotherapy, occupational therapy/ergotherapy, or social rehabilitation) should be instituted properly. PET imaging studies have suggested low doses are preferable. Clinical response was associated with at least 65% occupancy of D2 receptors, while greater than 72% was likely to cause hyperprolactinaemia and over 78% associated with extrapyramidal side effects. Doses of haloperidol greater than 5 mg increased the risk of side effects without improving efficacy. Patients responded with doses under even 2 mg in first-episode psychosis. For maintenance treatment of schizophrenia, an international consensus conference recommended a reduction dosage by about 20% every 6 months until a minimal maintenance dose is established.

Depot forms are also available; these are injected deeply intramuscularly at regular intervals. The depot forms are not suitable for initial treatment, but are suitable for patients who have demonstrated inconsistency with oral dosages.

The decanoate ester of haloperidol (haloperidol decanoate, trade names Haldol decanoate, Halomonth, Neoperidole) has a much longer duration of action, so is often used in people known to be noncompliant with oral medication. A dose is given by intramuscular injection once every two to four weeks. The IUPAC name of haloperidol decanoate is [4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]piperidin-4-yl] decanoate.

Topical formulations of haloperidol should not be used as treatment for nausea because research does not indicate this therapy is more effective than alternatives.

Adverse effects

Sources for the following lists of adverse effects

As haloperidol is a high-potency typical antipsychotic, it tends to produce significant extrapyramidal side effects. According to a 2013 meta-analysis of the comparative efficacy and tolerability of 15 antipsychotic drugs it was the most prone of the 15 for causing extrapyramidal side effects.

With more than 6 months months of use 14% percent of users gain weight.

Common (>1% incidence)

Extrapyramidal side effects including:

Dystonia (continuous spasms and muscle contractions)

Muscle rigidity

Akathisia (motor restlessness)

Parkinsonism (characteristic symptoms such as rigidity)

Hypotension

Anticholinergic side effects such as: (These adverse effects are more common than with lower-potency typical antipsychotics, such as chlorpromazine and thioridazine.)

Constipation

Dry mouth

Blurred vision

Somnolence (which is not a particularly prominent side effect, as is supported by the results of the aforementioned meta-analysis.)

Unknown frequency

Prolonged QT interval

Orthostatic hypotension

Increased respiratory rate

Anemia

Visual disturbances

Headache

Rare (<1% incidence)

Contraindications

Pre-existing coma, acute stroke

Severe intoxication with alcohol or other central depressant drugs

Known allergy against haloperidol or other butyrophenones or other drug ingredients

Known heart disease, when combined will tend towards cardiac arrest

Special cautions

Pre-existing Parkinson's disease or dementia with Lewy bodies

Patients at special risk for the development of QT prolongation (hypokalemia, concomitant use of other drugs causing QT prolongation)

Impaired liver function, as haloperidol is metabolized and eliminated mainly by the liver

In patients with hyperthyreosis, the action of haloperidol is intensified and side effects are more likely.

IV injections: risk of hypotension or orthostatic collapse

Patients with a history of leukopenia: a complete blood count should be monitored frequently during the first few months of therapy and discontinuation of the drug should be considered at the first sign of a clinically significant decline in white blood cells.

Elderly patients with dementia-related psychosis: analysis of 17 trials showed the risk of death in this group of patients was 1.6 to 1.7 times that of placebo-treated patients. Most of the causes of death were either cardiovascular or infectious in nature. It is not clear to what extent this observation is attributed to antipsychotic drugs rather than the characteristics of the patients. The drug bears a boxed warning about this risk.

Interactions

Other central depressants (alcohol, tranquilizers, narcotics): actions and side effects of these drugs (sedation, respiratory depression) are increased. In particular, the doses of concomitantly used opioids for chronic pain can be reduced by 50%.

Methyldopa: increased risk of extrapyramidal side effects and other unwanted central effects

Levodopa: decreased action of levodopa

Tricyclic antidepressants: metabolism and elimination of tricyclics significantly decreased, increased toxicity noted (anticholinergic and cardiovascular side effects, lowering of seizure threshold)

Lithium: rare cases of the following symptoms have been noted: encephalopathy, early and late extrapyramidal side effects, other neurologic symptoms, and coma.

Guanethidine: antihypertensive action antagonized

Epinephrine: action antagonized, paradoxical decrease in blood pressure may result

Amphetamine and methylphenidate: counteracts increased action of norepinephrine and dopamine in patients with narcolepsy or ADD/ADHD

Amiodarone: Q-Tc interval prolongation (potentially dangerous change in heart rhythm).

Other drugs metabolized by the CYP3A4 enzyme system: inducers such as carbamazepine, phenobarbital, and rifampicin decrease plasma levels and inhibitors such as quinidine, buspirone, and fluoxetine increase plasma levels

Symptoms

Symptoms are usually due to side effects. Most often encountered are:

Severe extrapyramidal side effects with muscle rigidity and tremors, akathisia, etc.

Hypotension or hypertension

Sedation

Anticholinergic side effects (dry mouth, constipation, paralytic ileus, difficulties in urinating, decreased perspiration)

Coma in severe cases, accompanied by respiratory depression and massive hypotension, shock

Rarely, serious ventricular arrhythmia (torsades de pointes), with or without prolonged QT-time

Treatment

Treatment is merely symptomatic and involves intensive care with stabilization of vital functions. In early detected cases of oral overdose, induction of emesis, gastric lavage, and the use of activated charcoal can all be tried. Epinephrine is avoided for treatment of hypotension and shock, because its action might be reversed. In the case of a severe overdose, antidotes such as bromocryptine or ropinirole may be used to treat the extrapyramidal effects caused by haloperidol, acting as dopamine receptor agonists. ECG and vital signs should be monitored especially for QT prolongation and severe arrhythmias should be treated with antiarrhythmic measures.

Prognosis

In general, the prognosis of overdose is good, and lasting damage is not known, provided the person has survived the initial phase. An overdose of haloperidol can be fatal.

Pharmacology

Haloperidol is a typical butyrophenone type antipsychotic that exhibits high affinity dopamine D₂ receptor antagonism and slow receptor dissociation kinetics. It has effects similar to the phenothiazines. The drug binds preferentially to D₂ and α₁ receptors at low dose (ED₅₀ = 0.13 and 0.42 mg/kg, respectively), and 5-HT₂ receptors at a higher dose (ED₅₀ = 2.6 mg/kg). Given that antagonism of D₂ receptors is more beneficial on the positive symptoms of schizophrenia and antagonism of 5-HT₂ receptors on the negative symptoms, this characteristic underlies haloperidol's greater effect on delusions, hallucinations and other manifestations of psychosis. Haloperidol's negligible affinity for histamine H₁ receptors and muscarinic M₁ acetylcholine receptors yields an antipsychotic with a lower incidence of sedation, weight gain, and orthostatic hypotension though having higher rates of treatment emergent extrapyramidal symptoms.

Haloperidol acts on these receptors: (K_i)

D₁ (silent antagonist) — Unknown efficiency

D₅ (silent antagonist) — Unknown efficiency

D₂ (inverse agonist) — 1.55 nM

D₃ (inverse agonist) — 0.74 nM

D₄ (inverse agonist) — 5–9 nM

σ₁ (irreversible inactivation by haloperidol metabolite HPP⁺) – 3 nM

σ₂ (agonist): 54 nM

5HT_1A receptor agonist – 1927 nM

5HT_2A (silent antagonist) – 53 nM

5HT_2C (silent antagonist) – 10,000 nM

5HT₆ (silent antagonist) – 3666 nM

5HT₇ (irreversible silent antagonist) — 377.2 nM

H₁ (silent antagonist) — 1,800 nM

M₁ (silent antagonist) — 10,000 nM

α_1A (silent antagonist) — 12 nM

α_2A (silent antagonist) — 1130 nM

α_2B (silent antagonist) — 480 nM

α_2C (silent antagonist) — 550 nM

NR1/NR2B subunit containing NMDA receptor (antagonist; ifenprodil site): IC₅₀ — 2,000 nM

Oral

The bioavailability of oral haloperidol ranges from 60–70%. However, there is a wide variance in reported mean T_max and T_1/2 in different studies, ranging from 1.7 to 6.1 hours and 14.5 to 36.7 hours respectively.

Intramuscular injections

The drug is well and rapidly absorbed with a high bioavailability when injected intramuscularly. The T_max is 20 minutes in healthy individuals and 33.8 minutes in patients with schizophrenia. The mean T_1/2 is 20.7 hours. The decanoate injectable formulation is for intramuscular administration only and is not intended to be used intravenously. The plasma concentrations of haloperidol decanoate reach a peak at about six days after the injection, falling thereafter, with an approximate half-life of three weeks.

Intravenous injections

The bioavailability is 100% in intravenous (IV) injection, and the very rapid onset of action is seen within seconds. The T_1/2 is 14.1 to 26.2 hours. The apparent volume of distribution is between 9.5 and 21.7 L/kg. The duration of action is four to six hours. If haloperidol is given as a slow IV infusion, the onset of action is slowed, and the duration of action is prolonged.

Therapeutic concentrations

Plasma levels of four to 25 micrograms per liter are required for therapeutic action. The determination of plasma levels can be used to calculate dose adjustments and to check compliance, particularly in long-term patients. Plasma levels in excess of the therapeutic range may lead to a higher incidence of side effects or even pose the risk of haloperidol intoxication.

The concentration of haloperidol in brain tissue is about 20-fold higher compared to blood levels. It is slowly eliminated from brain tissue, which may explain the slow disappearance of side effects when the medication is stopped.

Distribution and metabolism

Haloperidol is heavily protein bound in human plasma, with a free fraction of only 7.5 to 11.6%. It is also extensively metabolized in the liver with only about 1% of the administered dose excreted unchanged in the urine. The greatest proportion of the hepatic clearance is by glucuronidation, followed by reduction and CYP-mediated oxidation, primarily by CYP3A4.

History

Haloperidol was discovered by Paul Janssen. It was developed in 1958 at the Belgian company Janssen Pharmaceutica and submitted to the first of clinical trials in Belgium later that year.

Haloperidol was approved by the U.S. Food and Drug Administration (FDA) on April 12, 1967; it was later marketed in the U.S. and other countries under the brand name Haldol by McNeil Laboratories.

Brand names

Haloperidol is the INN, BAN, USAN, AAN approved name.

It is sold under the tradenames Aloperidin, Bioperidolo, Brotopon, Dozic, Duraperidol (Germany), Einalon S, Eukystol, Haldol (common tradename in the US and UK), Halosten, Keselan, Linton, Peluces, Serenace and Sigaperidol.

Veterinary use

Haloperidol is also used on many different kinds of animals. It appears to be particularly successful when given to birds, e.g., a parrot that will otherwise continuously pluck its feathers out.