Pimozide is classified as an atypical antipsychotic drug. It is structurally similar to another drug, haloperidol, which was the first drug to be used in Tourette's syndrome. Pimozide is most often used to treat symptoms of Tourette's syndrome, although it has also been used for treating schizophrenia mania, and other behavioral disorders.
Excess dopamine activity in the brain is associated with the verbal and physical tics observed in Tourette's syndrome. Like haloperidol, pimozide is believed to inhibit the actions of the brain chemical, dopamine.
Pimozide is broken down by the liver and eliminated from the body by the kidneys. Because pimozide is associated with health risks, it should not be used for tics that are simply annoying or cosmetic. Pimozide should be used only in patients with severe symptoms after other drug therapy has been tried and failed.
Pimozide is available in 1-mg and 2-mg tablets.
The common starting dose of pimozide in adults is 1-2 mg per day. The dose may be increased every other day until 0.2 mg per kg (or 0.9 mg per pound) of body weight per day or 10 mg per day is reached, whichever is less. Doses that exceed 0.2 mg per kg per day or 10 mg daily are not recommended.
In children, the usual initial dose is 0.05 mg per kg daily, and increased every three days to a maximum dose of 0.2 mg per kg (or 10 mg) per day.
Periodically, the dosage of pimozide should be reduced to determine if tics are still present. Patients should be maintained on the lowest dose that is effective in treating their disorder.
Pimozide should not be taken with grapefruit juice.
Pimozide should be used with close physician supervision by people who have a history of seizure disorders, because it may increase the tendency to have seizures.
Pimozide may cause extreme drowsiness and should be used carefully by people who need to be mentally alert.
Pimozide should not be used by people with mild tics, by individuals taking stimulants such as methylphenidate (Ritalin), pemoline (Cylert), or dextroamphetamine (Dexedrine) since these drugs may cause tics.
The most common side effects associated with pimozide are sleepiness, headache, stomach upset, muscle tightness, muscle weakness, difficulty moving, tremor, abnormal behavior, visual disturbances, and impotence.
Other side effects that might also occur with pimozide involve rapid heart rates or irregular heart rhythms, low blood pressure, constipation, dry mouth and eyes, rash, breast pain, breast milk production, loss of bladder control, or low blood cell counts.
Pimozide use may lead to the development of symptoms that resemble Parkinson's disease. These symptoms may include a tight or mask-like expression on the face,
Pimozide has the potential to produce a serious side effect called tardive dyskinesia. This syndrome consists of involuntary, uncoordinated movements that may appear late in therapy and not disappear even after the drug is stopped. Tardive dyskinesia involves involuntary movements of the tongue, jaw, mouth or face or other groups of skeletal muscles. The incidence of tardive dyskinesia increases with increasing age and with increasing dosage of pimozide. Women are at greater risk than men for developing tardive dyskinesia. There is no known effective treatment for tardive dyskinesia, although gradual (but rarely complete) improvement may occur over a long period.
An occasionally reported side effect of pimozide is neuroleptic malignant syndrome. This is a complicated and potentially fatal condition characterized by muscle rigidity, high fever, alterations in mental status, and cardiac symptoms such as irregular pulse or blood pressure, sweating, tachycardia (fast heartbeat), and arrhythmias (irregular heartbeat). People who think they may be experiencing any side effects from this or any other medication should talk to their physician promptly.
If pimozide is used with bethanechol (Urecholine), clonidine (Catapres), fluoxetine (Prozac), indomethacin (Indocin), meperidine (Demerol), paroxetine (Paxil), quinidine, or trazodone (Desyrel), the side effects associated with pimozide may be increased.
Some antibiotics, antifungals, antidepressants, and drugs used for AIDS may prevent the breakdown of pimozide by the liver and thus, increase the amount of pimozide in the body. The combination of pimozide and the above classes of drugs should be used cautiously if at all.
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Facts and Comparisons Staff. Drug Facts and Comparisons. 6th Edition. St. Louis, MO: A Wolter Kluwer Company, 2002.
Medical Economics Co. Staff. Physician's Desk Reference. 56th edition Montvale, NJ: Medical Economics Company, 2002.
Kelly Karpa, RPh, Ph.D.