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Thioridazine information from DrugsUpdate  

See Available Brands of Thioridazine in India

P - Caution when used during pregnancy
L - Caution when used during lactation
LI - Lab *

Thioridazine (Mellaril, Novoridazine, Thioril) is a piperidine antipsychotic drug belonging to the phenothiazine drug group and was previously widely used in the treatment of schizophrenia and psychosis. Due to concerns about cardiotoxicity and retinopathy at high doses this drug is not commonly prescribed, reserved for patients who have failed to respond to, or have contraindications for, more widely used antipsychotics. A serious side effect is the potentially fatal neuroleptic malignant syndrome. It exerts its actions through a central adrenergic-blocking, a dopamine-blocking and minor anticholinergic activity.

In older references, it is sometimes described as atypical, but more recently it is usually described as typical, with the term "atypical" usually reserved for agents showing D4 selectivity or serotonin antagonism.

Pharmacodynamics

Pharmacokinetics

Thioridazine, a phenothiazine antipsychotic, exhibits strong α-adrenergic blocking effects and depresses the release of hypothalamic and hypophyseal hormones by blocking postsynaptic mesolimbic, dopaminergic receptors in the brain.

Duration
4-5 days.

Distribution
Protein-binding (Thioridazine and metabolites): >95%. Crosses the placenta and is distributed into breast milk

Metabolism
Hepatic by the cytochrome P450 isoenzyme CYP2D6; converted to active metabolites, mesoridazine and sulforidazine.

Excretion

4-10 hours (plasma half-life).

Thioridazine Indications / Thioridazine Uses

Information Not Available

Thioridazine Adverse Reactions / Thioridazine Side Effects

Drowsiness, sedation, dry mouth, nasal congestion, blurring of vision, tremor, mydriasis, constipation, urinary retention, tachycardia, postural hypotension, sexual dysfunction, pigmentary retinopathy (high doses and prolonged therapy), contact dermatitis, tardive dyskinesias.

Potentially Fatal: Neuroleptic malignant syndrome. Sudden deaths due to cardiac arrhythmias and arrest.

Precautions

Leukopenia and/or agranulocytosis and convulsive seizures have been reported but are infrequent. In schizophrenic patients with epilepsy, anticonvulsant medication should be maintained during treatment with Thioridazine. Pigmentary retinopathy, which has been observed primarily in patients taking larger than recommended doses, is characterized by diminution of visual acuity, brownish coloring of vision, and impairment of night vision; examination of the fundus discloses deposits of pigment. The possibility of this complication may be reduced by remaining within the recommended limits of dosage.

Overdosage
Overdosage may produce effects that are extensions of the adverse reactions. Extrapyramidal reactions, hypotension, sedation, CNS depression progressing to coma or CNS stimulation with convulsions followed by respiratory depression, shock (e.g. ECG changes and cardiac arrhythmias), increased QT and PR intervals, non-specific ST and T wave changes, torsades de pointes, myocardial depression, agitation, urinary retention, oliguria, uremia, blurring of vision, hypothermia, hyperthermia, mydriasis, miosis, tremor, muscle twitching, rigidity, seizures, muscular hypotonia, respiratory and/or vasomotor collapse and pulmonary oedema. Treatment is symptomatic and supportive with ECG monitoring for at least 24 hours or as long as QT interval is prolonged. A patent airway should be established and adequate oxygenation and ventilation maintained. Emesis (less preferable due to risk of dystonia and potential of aspiration of vomitus) or gastric lavage followed by repeated doses of activated charcoal. Management of arrhythmias include ventricular pacing, defibrillation, admin of IV magnesium sulfate, lidocaine, phenytoin or isoproterenol with correction of electrolyte abnormalities and acid-base balance. Lidocaine should be admin cautiously due to increased risk of seizures.

Special Precautions

Pregnancy, lactation; renal or hepatic impairment, epilepsy. Perform ECG screening and electrolyte measurement before therapy, after each dose increase and at 6-monthly intervals. Monitor for visual defects on long-term therapy. May impair ability to perform skilled tasks. Withdrawal of drug to be carried out gradually over 1-2 weeks.

Other Drug Interactions

Potentiates adverse effects of anticholinergics. Concurrent use of TCAs leads to raised blood levels of both drugs. May antagonise effects of levodopa, bromocriptine and other dopamine agonists. Avoid co-admin with drugs that cause electrolyte imbalance. Monitor phenytoin therapy due to inconsistent effects of thioridazine on phenytoin levels.

Potentially Fatal: Increased risk of QT prolongation with class IA and class II antiarrhythmics, astemizole, cisapride, pimozide, droperidol, erythromycin IV, sparfloxacin, terfenadine, clarithromycin and other drugs that may prolong QT interval. Potentiates CNS depression with opioids. Increased risk of arrhythmias with ephedrine-like drugs e.g. phenylpropanolamine. Increased thioridazone levels with fluovoxamine, pindolol, propranolol, ritonavir and other CYP2D6 isoenzymes inhibitors (e.g. fluoxetine, paroxetine).

Other Interactions

Information Not Available

Dosage

Oral
Schizophrenia
Adult: Initially, 50-100 tid daily and slowly titrated upwards at no more than 100 mg weekly. Max: 800 mg daily in 2-4 divided doses.
Child: 2–12 years: Initially, 0.5 mg/kg daily in divided doses, increased gradually until optimum effect obtained. Max: 3 mg/kg daily.

Renal impairment: Lower initial doses and more gradual dosage increase.
Hepatic impairment: Lower initial doses and more gradual dosage increase.

Oral
Depression
Adult: Initially, 25 mg tid, titrated to 20–200 mg daily.

Renal impairment: Lower initial doses and more gradual dosage increase.
Hepatic impairment: Lower initial doses and more gradual dosage increase.

Incompatibility

Oral liquid thioridazine should not be admin simultaneously with carbamazepine oral suspension.

Food(before/after)

Should be taken with food

List of Contraindications

Thioridazine and Pregnancy

Caution when used during pregnancy

Category C: Either studies in animals have revealed adverse effects on the foetus (teratogenic or embryocidal or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the foetus.

Thioridazine and Lactation

Caution when used during lactation

Thioridazine and Children

Information Not Available

Thioridazine and Geriatic

Information Not Available

Thioridazine and Other Contraindications

Hypersensitivity to phenothiazines, comatose states, pre-exisitng CNS depression, severe CVS disorders, uncorrected hypokalaemia or any electrolyte imbalance, known or suspected QT prolongation, history of ventricular arrhythmias including torsades de pointes and porphyria. Bone-marrow suppression, phaeochromocytoma, or prolactin-dependent tumours, angle-closure glaucoma, history of jaundice, parkinsonism, DM, hypothyroidism, myasthenia gravis, paralytic ileus, prostatic hyperplasia, or urinary retention. Patients with reduced activity of cytochrome P450 isoenzyme CYP2D6.

Storage

Oral
Tablet/oral concentrate: Store 15-30°C

Lab interference

Oral
Tablet/oral concentrate: Store 15-30°C

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