THIORIDAZINE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Thioridazine is a typical antipsychotic of the phenothiazine class. It blocks postsynaptic dopamine D2 receptors in the mesolimbic system, and also has significant anticholinergic and alpha-adrenergic blocking activity. It exhibits a high affinity for D2, 5-HT2A, and alpha1-adrenergic receptors.
| Metabolism | Extensively metabolized in the liver via CYP2D6 to active metabolites (e.g., mesoridazine, sulforidazine). Thioridazine is also a potent inhibitor of CYP2D6. |
| Excretion | Primarily hepatic metabolism with <1% excreted unchanged in urine; metabolites are excreted renally (approximately 30% of dose as metabolites) and fecally (approximately 20-30% via bile). |
| Half-life | 24-36 hours for the parent drug; extended in hepatic impairment and elderly; steady-state reached in 4-7 days. |
| Protein binding | 95-99% bound primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 10-20 L/kg, indicating extensive tissue binding and distribution. |
| Bioavailability | Oral: approximately 40-50% due to first-pass metabolism; not available in parenteral form. |
| Onset of Action | Oral: 30-60 minutes to onset of sedation and antipsychotic effects; peak effects at 2-4 hours. Not available parenterally. |
| Duration of Action | 6-12 hours for single oral dose; longer with chronic dosing due to accumulation; antipsychotic effects persist for days after discontinuation. |
| Molecular Weight | 407.05 |
Adults: Initial 50-100 mg orally three times daily, gradually increasing to maximum 800 mg/day in divided doses. Usual maintenance: 200-800 mg/day.
| Dosage form | CONCENTRATE |
| Renal impairment | Contraindicated in severe renal impairment (CrCl <10 mL/min). For moderate impairment (CrCl 10-50 mL/min), use 50-75% of normal dose with careful monitoring. |
| Liver impairment | Contraindicated in significant hepatic impairment. For mild impairment (Child-Pugh A), reduce dose by 50% and monitor. Avoid in Child-Pugh B or C. |
| Pediatric use | Contraindicated in children <2 years. For children ≥2 years: 0.5-3 mg/kg/day orally in divided doses, maximum 3 mg/kg/day or 200 mg/day (whichever less). |
| Geriatric use | Initial dose 10-25 mg orally once or twice daily, titrate slowly. Use lowest effective dose due to increased risk of QT prolongation and anticholinergic effects. |
| 1st trimester | Avoid. Case reports of fetal abnormalities; possible risk of teratogenicity. |
| 2nd trimester | Avoid. May cause fetal or neonatal harm; no well-controlled studies. |
| 3rd trimester | Avoid. Risk of extrapyramidal symptoms and withdrawal in neonates; use only if clearly needed. |
Clinical note
Strong CYP2D6 inhibitors are contraindicated due to risk of QT prolongation Can cause QT prolongation and retinopathy.
| Placental transfer | Crosses placenta; detected in fetal blood and tissues. |
| Breastfeeding | Excreted into breast milk; potential for sedation, apnea, and neurodevelopment issues; avoid breastfeeding or use alternative. |
| Lactation Rating |
■ FDA Black Box Warning
Thioridazine has been shown to prolong the QTc interval in a dose-dependent manner, and is associated with an increased risk of sudden death. It is contraindicated in patients with congenital long QT syndrome or a history of cardiac arrhythmias. It should not be used with other drugs that prolong the QTc interval or in patients with electrolyte imbalances. Use is restricted to patients with schizophrenia who have failed to respond to at least two other antipsychotics.
| Common Effects | Extrapyramidal symptoms |
| Serious Effects |
Comatose statesCNS depressionQT interval prolongation (congenital or acquired)Concomitant use with QT-prolonging drugsSevere hypotensionKnown hypersensitivity
| Precautions | QT prolongation and risk of torsades de pointes; perform ECG before and during therapy, Neuroleptic malignant syndrome (NMS); hyperthermia, rigidity, autonomic instability, Tardive dyskinesia with long-term use, Anticholinergic effects: constipation, urinary retention, blurred vision, Hypotension, especially orthostatic, Seizure threshold lowering, Hepatic impairment, Coadministration with drugs that inhibit CYP2D6 or prolong QTc, Avoid in elderly with dementia-related psychosis due to increased mortality |
Loading safety data…
| L5 |
| Teratogenic Risk | First trimester: Limited human data, but animal studies show fetal toxicity at high doses. Second/third trimester: Risk of extrapyramidal symptoms and neonatal withdrawal. Avoid in pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal ECG for QT prolongation, maternal blood pressure, liver function. Fetal: assess growth and neonatal behavior after delivery. |
| Fertility Effects | May cause hyperprolactinemia leading to menstrual irregularities and reduced fertility in women. Reversible upon discontinuation. |
| Food/Dietary | Avoid grapefruit and grapefruit juice, which may increase thioridazine plasma levels. Take with food or milk if gastrointestinal upset occurs. Avoid tyramine-rich foods (e.g., aged cheeses, cured meats) if receiving concurrent MAO inhibitor. Maintain adequate hydration to mitigate anticholinergic effects. |
| Clinical Pearls | Thioridazine is a first-generation antipsychotic with significant cardiotoxic potential; it is contraindicated in patients with QTc interval >450 ms, those receiving drugs that prolong QTc, or those with pre-existing cardiac conditions. Monitor ECG and serum potassium/magnesium before and during therapy. Due to risk of retinopathy, avoid doses >800 mg/day. Taper slowly to avoid withdrawal dyskinesia. Use with caution in elderly patients with dementia-related psychosis due to increased mortality risk. |
| Patient Advice | This medication can cause serious heart rhythm problems; inform your doctor immediately if you experience fainting, palpitations, or irregular heartbeat. · Avoid alcohol and other central nervous system depressants, as they can increase drowsiness and dizziness. · Do not suddenly stop taking this medication; gradual dose reduction is necessary under medical supervision. · Report any vision changes, such as blurred vision, brownish discoloration of vision, or difficulty reading. · This drug may cause orthostatic hypotension; rise slowly from sitting or lying positions. · Avoid sun exposure and use sunscreen, as thioridazine can increase photosensitivity. |