Pimozide

Pimozide carries orphan drug designation from the FDA for Tourette syndrome, granted in 1985. It is specifically reserved for patients whose tics severely compromise daily functioning and who have not responded adequately to haloperidol. The drug is not intended for simple tics, cosmetically troublesome tics, or as a first-line agent. The two pivotal controlled trials enrolled patients aged 8 to 53 years, with the majority being 12 years or older (FDA PI).

Mechanism of Action

Pimozide is a high-potency dopamine receptor antagonist belonging to the diphenylbutylpiperidine class. Its primary therapeutic action in Tourette syndrome arises from potent blockade of dopamine D₂ receptors in the basal ganglia, which suppresses the abnormal motor and vocal tic circuitry. Pimozide also shows affinity for D₃ and D₄ receptor subtypes, and acts as a 5-HT₇ receptor antagonist. Additionally, it blocks hERG potassium channels, which accounts for the clinically significant QT interval prolongation. Its calcium channel blocking properties and anticholinergic activity contribute to both its neurological effects and its side effect burden. On a milligram-per-milligram basis, pimozide is approximately 50–70 times more potent than chlorpromazine and more potent than haloperidol.

ADME Profile

Pimozide is metabolised primarily by CYP3A4 and to a lesser extent CYP1A2. It also directly blocks hERG potassium channels, producing QT prolongation independent of plasma levels. This dual vulnerability — metabolic inhibition raising drug levels plus additive pharmacodynamic QT effects — makes pimozide one of the most interaction-sensitive drugs in clinical use. The FDA label lists numerous contraindicated combinations.

Absolute Contraindications

• Congenital long QT syndrome or history of cardiac arrhythmias
• Uncorrected hypokalaemia or hypomagnesaemia
• Concurrent use of CYP3A4 inhibitors: macrolide antibiotics (clarithromycin, erythromycin, azithromycin, dirithromycin, troleandomycin), azole antifungals (itraconazole, ketoconazole), HIV protease inhibitors (ritonavir, indinavir, nelfinavir, saquinavir), nefazodone
• Concurrent use of SSRIs: sertraline, citalopram, escitalopram (specifically named in FDA label)
• Concurrent use of other QT-prolonging drugs: Class Ia/III antiarrhythmics, thioridazine, ziprasidone, mesoridazine, droperidol, and others (see Drug Interactions)
• Grapefruit juice consumption
• Severe CNS depression or comatose states
• Hypersensitivity to pimozide
• Treatment of simple tics or tics not associated with Tourette syndrome
• Patients on tic-inducing drugs (methylphenidate, amphetamines, pemoline) — must withdraw these drugs first to confirm tics are not drug-induced

Relative Contraindications (Specialist Input Recommended)

• Hepatic impairment: Pimozide is extensively hepatically metabolised; reduced clearance may elevate levels unpredictably. No specific dose adjustment guidelines exist. Use only if benefit clearly outweighs risk with close ECG monitoring.
• Renal impairment: Approximately 40% of drug is renally excreted as metabolites. Use with caution; no formal dose adjustment defined.
• History of breast cancer: Pimozide elevates prolactin. Approximately one-third of breast cancers may be prolactin-dependent; the clinical significance of antipsychotic-induced hyperprolactinaemia is not fully resolved.
• Elderly patients: Higher risk of tardive dyskinesia, orthostatic hypotension, and cardiac events. Start at lowest dose with careful ECG monitoring.
• Patients with seizure history or EEG abnormalities: Pimozide may lower the seizure threshold. Maintain adequate anticonvulsant coverage.

Use with Caution

• Conditions aggravated by anticholinergic activity (urinary retention, narrow-angle glaucoma, paralytic ileus)
• Patients at risk for orthostatic hypotension (dehydration, cardiovascular disease, concurrent antihypertensives)
• Children under 12 years (limited safety data)
• Patients with Parkinson disease or dementia with Lewy bodies (risk of severe extrapyramidal exacerbation)

1. ORAP (pimozide) tablets prescribing information. Gate Pharmaceuticals (Teva). Revised January 2008. FDA Label Primary regulatory source for all FDA-approved dosing, contraindications, adverse reactions, and warnings cited throughout this monograph.
2. Pimozide tablets, USP prescribing information. Endo USA, Inc. NDC Label Generic formulation labelling; confirms dosing and side effect data consistent with branded Orap.

3. Shapiro E, Shapiro AK, Fulop G, et al. Controlled study of haloperidol, pimozide, and placebo for the treatment of Gilles de la Tourette’s syndrome. Arch Gen Psychiatry. 1989;46(8):722-730. DOI One of two pivotal controlled trials supporting FDA approval of pimozide for Tourette syndrome; established efficacy and adverse event profile.
4. Sallee FR, Nesbitt L, Jackson C, et al. Relative efficacy of haloperidol and pimozide in children and adolescents with Tourette’s disorder. Am J Psychiatry. 1997;154(8):1057-1062. DOI Comparative trial demonstrating similar efficacy of pimozide and haloperidol in pediatric Tourette syndrome with differing side effect profiles.
5. Regeur L, Pakkenberg B, Fog R, Pakkenberg H. Clinical features and long-term treatment with pimozide in 65 patients with Gilles de la Tourette’s syndrome. J Neurol Neurosurg Psychiatry. 1986;49(7):791-795. DOI Long-term observational data on pimozide use in Tourette syndrome informing maintenance dosing and tolerability expectations.

6. Pringsheim T, Okun MS, Müller-Vahl K, et al. Practice guideline recommendations summary: Treatment of tics in people with Tourette syndrome and chronic tic disorders. Neurology. 2019;92(19):896-906. DOI AAN evidence-based guideline positioning antipsychotics including pimozide in the treatment algorithm for Tourette syndrome.
7. Roessner V, Plessen KJ, Rothenberger A, et al. European clinical guidelines for Tourette syndrome and other tic disorders. Part II: pharmacological treatment. Eur Child Adolesc Psychiatry. 2011;20(4):173-196. DOI European consensus guidelines covering pimozide’s place among antipsychotic options for tic disorders, with attention to cardiac monitoring requirements.

8. Pimozide. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. National Institute of Diabetes and Digestive and Kidney Diseases. Updated 2020. NCBI Comprehensive review of pimozide hepatotoxicity data (minimal risk) and CYP metabolism characterisation including CYP2D6 contribution.
9. Flockhart DA. Drug Interactions: Cytochrome P450 Drug Interaction Table. Indiana University School of Medicine. Link Reference database for CYP3A4 and CYP1A2 substrates and inhibitors relevant to pimozide interaction risk assessment.

10. Sallee FR, Pollock BG, Stiller RL, Stull S, Everett G, Perel JM. Pharmacokinetics of pimozide in adults and children with Tourette’s syndrome. J Clin Pharmacol. 1987;27(10):776-781. DOI Key study establishing half-life differences between children (~66 h) and adults (~111 h) with Tourette syndrome.
11. Pimozide monograph. AHFS Drug Information. American Society of Health-System Pharmacists. Revised June 2024. Drugs.com Comprehensive professional monograph summarising absorption, distribution, metabolism, excretion, and clinical use data across populations.
12. Sandor P, Musisi S, Moldofsky H, Lang A. Tourette syndrome: a follow-up study of 33 patients. J Clin Psychopharmacol. 1990;10(3):197-199. DOI Long-term naturalistic follow-up (up to 15 years) documenting pimozide effectiveness at dose range 2–18 mg in Tourette syndrome patients aged 9–50.