THIORIDAZINE HYDROCHLORIDE INTENSOL
Clinical safety rating: safe
Strong CYP2D6 inhibitors are contraindicated due to risk of QT prolongation Can cause QT prolongation and retinopathy.
Thioridazine is a typical antipsychotic of the phenothiazine class. It blocks dopamine D2 receptors in the brain, particularly in the mesolimbic pathway, and also exhibits antagonism at alpha-adrenergic, histaminergic H1, and muscarinic M1 receptors.
| Metabolism | Extensively metabolized in the liver primarily via CYP2D6, with minor contributions from CYP1A2 and CYP3A4. Major metabolites include mesoridazine (active) and sulforidazine (active). |
| Excretion | Primarily hepatic metabolism with <1% excreted unchanged in urine; metabolites eliminated in bile and feces. Approx. 30–40% of a dose appears in urine as metabolites (mostly sulfoxides and side-chain oxidized products) and 50–60% in feces. |
| Half-life | Terminal elimination half-life ranges from 21 to 30 hours (mean 24 h). In elderly or patients with hepatic impairment, half-life may be prolonged. Requires multiple days to reach steady state. |
| Protein binding | 95–97% bound, primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Approximately 9–18 L/kg (mean 12 L/kg), indicating extensive tissue distribution and high lipophilicity. |
| Bioavailability | Oral bioavailability is approximately 60% due to first-pass metabolism. Concentrated oral solution (Intensol) has equivalent bioavailability to tablets. |
| Onset of Action | Oral: 30–60 minutes for initial tranquilizing effect; antipsychotic effect may take days to weeks. Not administered parenterally; oral concentrated solution (Intensol) onset similar to tablets. |
| Duration of Action | Single oral dose: clinical effects persist 4–6 hours; antipsychotic effect sustained with regular dosing. Duration of D2 receptor blockade is longer than symptomatic effects. |
| Molecular Weight | 370.58 Da |
50 mg orally twice daily initially, titrated to 200-800 mg/day in divided doses. Maximum 800 mg/day.
| Dosage form | CONCENTRATE |
| Renal impairment | No specific GFR-based adjustments; contraindicated in severe renal impairment (CrCl <10 mL/min) due to risk of accumulation. |
| Liver impairment | Contraindicated in Child-Pugh class C (severe hepatic impairment). In Child-Pugh class A or B, use with caution and reduce dose by 25-50%. |
| Pediatric use | 2-12 years: 0.5-3 mg/kg/day orally in divided doses. Maximum: 3 mg/kg/day (not to exceed adult max). Not recommended under 2 years. |
| Geriatric use | Initial dose 10 mg orally twice daily; increase slowly by 10-25 mg increments. Maximum 200 mg/day due to increased sensitivity and risk of QTc prolongation. |
| 1st trimester | Thioridazine is contraindicated in first trimester due to risk of congenital malformations, particularly neural tube defects and cardiovascular anomalies. |
| 2nd trimester | Limited data; may be used if benefit outweighs risk, but avoid if possible due to potential adverse effects on fetal development. |
| 3rd trimester | Avoid in third trimester; may cause extrapyramidal symptoms and withdrawal in neonate, including agitation, hypertonia, and respiratory distress. |
Clinical note
Strong CYP2D6 inhibitors are contraindicated due to risk of QT prolongation Can cause QT prolongation and retinopathy.
| FDA category | Animal |
| Placental transfer | Thioridazine crosses the placenta; fetal plasma levels can reach 50-80% of maternal levels based on animal studies. |
■ FDA Black Box Warning
Thioridazine can cause dose-related QTc interval prolongation, which may lead to torsades de pointes and sudden death. It is contraindicated with other drugs that prolong QTc. Use is restricted to patients with schizophrenia who fail to respond to other antipsychotics.
| Common Effects | Extrapyramidal symptoms |
| Serious Effects |
Hypersensitivity to thioridazine or phenothiazinesComatose states or CNS depressionHistory of QT prolongation or congenital long QT syndromeConcurrent use of medications that prolong QT interval (e.g., class IA/III antiarrhythmics, some antibiotics)
| Precautions | Risk of QTc prolongation and torsades de pointes; avoid use with other QTc-prolonging drugs or conditions (e.g., electrolyte disturbances, bradycardia). Neuroleptic malignant syndrome (NMS). Tardive dyskinesia. Orthostatic hypotension. Impaired hepatic or renal function. Elderly patients with dementia-related psychosis have increased risk of death. Seizure threshold lowering. Leukopenia/agranulocytosis. Anticholinergic effects (urinary retention, constipation, blurred vision). |
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| Breastfeeding |
| Thioridazine is excreted into breast milk at low concentrations but can accumulate in nursing infants. Reports of drowsiness and developmental concerns. Use with caution; consider alternative antipsychotics with better safety profiles. |
| Lactation Rating | L4 - Possibly Hazardous |
| Teratogenic Risk | First trimester: Limited data; potential risk of congenital anomalies based on animal studies and case reports, but not confirmed in human studies. Second and third trimesters: Extrapyramidal symptoms and withdrawal in neonates exposed late in pregnancy; avoid use unless essential. |
| Fetal Monitoring | Monitor maternal ECG for QTc prolongation, liver function tests, complete blood count, and ophthalmologic exams. Fetal monitoring for growth and development if used in pregnancy; assess neonatal for extrapyramidal symptoms and withdrawal after delivery. |
| Fertility Effects | May cause hyperprolactinemia leading to menstrual irregularities, anovulation, or galactorrhea, potentially impairing fertility. Effects are reversible upon discontinuation. |
| Food/Dietary | Avoid grapefruit juice; may increase thioridazine levels and risk of side effects. Limit alcohol intake as it may enhance CNS depression. No specific dietary restrictions beyond caution with tyramine-rich foods? (Not typically required for thioridazine, but advise balanced diet to manage weight and metabolic effects.) |
| Clinical Pearls | Monitor ECG for QTc prolongation; contraindicated with drugs that prolong QTc or with known QTc prolongation. Titrate slowly from low doses to avoid orthostatic hypotension and anticholinergic effects. May lower seizure threshold; use cautiously in epilepsy. Risk of tardive dyskinesia with long-term use. Avoid in patients with pheochromocytoma or history of blood dyscrasias. |
| Patient Advice | Take exactly as prescribed; do not stop abruptly without consulting your doctor. · Avoid alcohol and grapefruit juice. · May cause drowsiness; do not drive or operate machinery until you know how thioridazine affects you. · Stand up slowly to prevent dizziness. · Report any symptoms of irregular heartbeat, fainting, or seizures immediately. · May cause dry mouth; use sugarless gum or candy. · Avoid excessive sun exposure; use sunscreen. · Notify your doctor if you have unexplained fever, muscle stiffness, or confusion. |