How haloperidol works
Haloperidol is a highly effective antipsychotic from the butyrophenone class. It is around 50 times more effective than the comparative substance chlorpromazine and is the drug of choice for acute psychoses and psychomotor agitation (movement behavior influenced by mental processes).
In the brain, the individual nerve cells (neurons) communicate with each other via various messenger substances (neurotransmitters). A cell releases a neurotransmitter that binds to specific docking sites (receptors) of other cells and thus transmits information.
In order to terminate the signal, the first (releasing) nerve cell takes up the neurotransmitter again. Neurotransmitters can be roughly divided into two groups: Some have a more stimulating, activating and exciting effect, such as noradrenaline.
The others trigger dampening and calming effects, such as GABA, or influence mood, such as serotonin – a “happiness hormone”. The other “happiness hormone” is dopamine. In excess, it leads to psychosis, schizophrenia, delusions and loss of reality.
Those treated then perceive their environment more realistically again and no longer suffer from delusions. Highly effective antipsychotics such as haloperidol also have a strong anti-emetic effect, which is also used medically.
Extrapyramidal disorders as a side effect
If there is a lack of dopamine (as occurs in Parkinson’s disease), the body’s movement processes are disrupted. The blockade of dopamine signals by haloperidol (or other classic antipsychotics) can also cause this effect.
This side effect on the so-called extrapyramidal-motor system is also referred to as extrapyramidal (motor) syndrome (EPS). In the past, this side effect was even seen as a correlate of efficacy, but this was revised with the discovery of atypical neuroleptics.
Absorption, breakdown and excretion
After ingestion, haloperidol is rapidly and completely absorbed in the intestine. Before the active ingredient reaches the large bloodstream, around a third is already broken down in the liver (so-called “first-pass effect”).
The highest blood levels are measured two to six hours after ingestion. Haloperidol is broken down in the liver via the cytochrome P450 enzyme system.
When is haloperidol used?
Haloperidol is approved for the treatment of:
- Acute and chronic schizophrenia
- Acute mania
- Acute delirium (clouding of consciousness)
- Acute psychomotor agitation
- Aggression and psychotic symptoms in dementia
- Tic disorders including Tourette’s syndrome (here, however, haloperidol is only used as a last resort)
- Mild to moderate Huntington’s disease (rare inherited disorder of the central nervous system)
- Aggression in children with autism or developmental disorders after other measures have failed
- Postoperative nausea and vomiting
In principle, haloperidol can be taken over a longer period of time. However, the benefit of the therapy should be reviewed regularly, as the risk of side effects increases with the duration of therapy.
How haloperidol is used
Haloperidol is usually administered as a tablet if the treatment is not carried out as an inpatient in a clinic. Haloperidol drops and oral solution (“juice”) are also available for self-administration.
Treatment is usually started at a low dose (one to ten milligrams of haloperidol per day, divided into up to three doses) and slowly increased. In this way, the lowest effective dose can be determined individually.
It is taken in one to three doses with a glass of water, preferably with meals.
To end the therapy, it must be “phased out”. The dosage is therefore reduced slowly and gradually to prevent increased side effects.
What are the side effects of haloperidol?
At a low dosage (up to two milligrams per day), side effects occur only rarely and are usually of a temporary nature.
Over ten percent of those treated develop haloperidol side effects such as restlessness, urge to move, involuntary movements (extrapyramidal disorders), insomnia and headaches.
In addition, one in ten to one hundred of those treated experience side effects such as psychotic disorders, depression, tremors, mask face, high blood pressure, drowsiness, slowness of movement and movement disorders, dizziness, visual disturbances and low blood pressure (especially when standing up from a lying or sitting position).
Constipation, dry mouth, increased salivation, nausea, vomiting, abnormal liver function values, skin rashes, weight gain or loss, urinary retention and potency disorders have also been observed.
What should be considered when taking haloperidol?
Contraindications
Haloperidol must not be used in the following cases
- comatose states
- Depression of the central nervous system
- Parkinson’s disease
- Lewy body dementia (special form of dementia)
- severe heart failure
- recent myocardial infarction
- potassium deficiency
- certain forms of cardiac arrhythmia
Interactions
Drugs that affect the heart rhythm (more precisely, prolong the QT time) can lead to severe cardiac arrhythmia and cardiac arrest if taken at the same time as haloperidol.
These include, for example, certain antiarrhythmic drugs (quinidine, procainamide), antibiotics (erythromycin, clarithromycin), allergy medications (astemizole, diphenhydramine) and antidepressants (fluoxetine, citalopram, amitriptyline).
Many active substances are broken down in the liver via the same enzymes (cytochrome P450 3A4 and 2D6) as haloperidol. If administered at the same time, this can lead to faster or slower degradation of one or more of the active substances administered and possibly also to more severe side effects.
This applies, for example, to certain antifungal drugs (ketoconazole, itraconazole), drugs for epilepsy and seizures (carbamazepine, phenytoin), psychotropic drugs (alprazolam, buspirone, chlorpromazine) and especially drugs for depression (venlafaxine, fluoxetine, sertraline, amitriptyline, imipramine).
Haloperidol can also interact with anticoagulants, which is why coagulability should be closely monitored during combined treatment.
Age restriction
Suitable preparations of haloperidol can be administered to children from the age of three. Tablets are approved from the age of six. The dosage depends on body weight.
A dose reduction of haloperidol may be necessary in older patients and those with liver dysfunction.
Pregnancy and breastfeeding
Haloperidol should only be taken in exceptional cases during pregnancy. Although studies have not shown any direct harmful effects on the child, taking it shortly before birth can lead to adaptation disorders in the newborn.
Breastfeeding is acceptable with low doses (less than 5 milligrams per day) and good observation of the child. However, if unexplained symptoms such as movement disorders, tiredness, difficulty drinking or restlessness occur in the child, it is advisable to discuss this with the prescribing doctor.
How to obtain medication with haloperidol
Haloperidol is available on prescription in Germany, Austria and Switzerland in any dosage and quantity and is only available in pharmacies
How long has haloperidol been known?
The antipsychotic haloperidol was discovered by the doctor and chemist Paul Janssen and registered for clinical trials in 1958. It was first approved in Belgium in 1959 and later throughout Europe.
