Thioridazine


Concise Prescribing Info
Indications/Uses
Schizophrenia.
Dosage/Direction for Use
Adult : PO Patient who fail to respond adequately with other antipsychotic therapy: Initial: 50-100 mg tid. Dose may be gradually increased if necessary, according to response and tolerability. Usual dose: 200-800 mg/day in 2-4 divided doses. Max: 800 mg/day. Individualise dose and use the smallest effective dosage.
Dosage Details
Oral
Schizophrenia
Adult: In patient who fail to respond adequately with other antipsychotic therapy: Initially, 50-100 mg tid, dose may be gradually increased if necessary, according to response and tolerability. Usual dose range: 200-800 mg daily in 2-4 divided doses. Max: 800 mg daily. Individualise dose and use the smallest effective dosage.
Renal Impairment
Lower initial dose and more gradual dosage increase.
Hepatic Impairment
Lower initial dose and more gradual dosage increase.
Administration
Should be taken with food.
Contraindications
Severe CNS depression, hyper- or hypotensive heart disease; comatose states, congenital long QT syndrome or history of cardiac arrhythmias. Known genetic defect leading to reduced CYP2D6 activity. Concomitant use with CYP2D6 inhibitors (e.g. fluoxetine, paroxetine), fluvoxamine, propranolol or pindolol, or other drugs known to prolong QTc interval.
Special Precautions
Patient with decreased gastrointestinal motility, paralytic ileus, urinary retention, benign prostatic hyperplasia, xerostomia, visual problems, Lewy body or Parkinson disease dementia; at risk of aspiration pneumonia (e.g. Alzheimer’s disease), seizure, and orthostatic hypotension or with condition that may not tolerate transient hypotensive episodes (e.g. cerebrovascular disease, CV disease, hypovolaemia); pre-existing low WBC or history of drug-induced leucopenia/neutropenia. Patient subjected to heat exposure, strenuous exercise and dehydration. Renal and hepatic impairment. Elderly with dementia-related psychosis. Pregnancy and lactation. Avoid abrupt withdrawal.
Adverse Reactions
Significant: Anticholinergic effects (e.g. constipation, xerostomia, blurred vision, urinary retention), blood dyscrasias (e.g. leucopenia, neutropenia), oesophageal dysmotility and aspiration, extrapyramidal symptoms (e.g. pseudoparkinsonism, acute dystonic reactions, akathisia, tardive dyskinesia), hyperprolactinemia, pigmentary retinopathy, orthostatic hypotension, impaired core body temperature regulation; somnolence, postural hypotension, motor and sensory stability resulting to falls and fractures; convulsive seizures.
Eye disorders: Visual disturbance.
Gastrointestinal disorders: Diarrhoea, nausea, vomiting.
General disorders and administration site conditions: Lethargy.
Investigations: Weight gain, ECG changes.
Metabolism and nutrition disorders: Peripheral oedema.
Nervous system disorders: Drowsiness, headache, restlessness.
Psychiatric disorders: Confusion, hyperactive behavior, psychotic reaction, insomnia, depression, agitation.
Reproductive system and breast disorders: Amenorrhoea, galactorrhoea, breast engorgement, sexual dysfunction.
Respiratory, thoracic and mediastinal disorders: Nasal congestion.
Skin and subcutaneous tissue disorders: Dermatitis, hyperpigmentation, pallor, rash, urticaria. Rarely, photosensitivity.
Potentially Fatal: QTc interval prolongation (dose-related) resulting to Torsades de Pointes; agranulocytosis, neuroleptic malignant syndrome.
Patient Counseling Information
This drug may impair physical and mental abilities, if affected, do not drive or operate machinery.
MonitoringParameters
Perform ECG and monitor serum K at baseline then periodically, thereafter. Monitor mental status; vital signs and CBC as clinically indicated; weight, height, BMI, and circumference at baseline, every visit for the 1st 6 months then quarterly with stable dose; liver function annually and as clinically indicated; fasting plasma glucose level/HbA1c at baseline (repeat 4 months after the initial treatment in at risk patients) then annually; lipid panel at baseline then every 2 years (or every 6 months as clinically indicated). Monitor for changes in menstruation, libido, development of galactorrhoea, erectile and ejaculatory function, abnormal involuntary movements or parkinsonian signs, tardive dyskinesia, visual changes, and fall risk. Assess ophthalmic exam at baseline and periodically, thereafter.
Overdosage
Symptoms: Constipation, oliguria, uraemia, apnoea, pulmonary oedema, mydriasis, miosis, dry skin or mouth, nasal congestion, sedation, extrapyramidal effects, confusion, agitation, cardiac arrhythmias, hypotension, ECG changes, bradycardia, sinus tachycardia. Management: Supportive and symptomatic treatment. Establish and maintain airway and ensure adequate oxygenation and ventilation. Initiate CV monitoring immediately including continuous ECG monitoring to detect possible arrhythmias. In case of thioridazine-induced arrhythmias, management may include ventricular pacing, defibrillation and administration of IV Mg sulfate, phenytoin, lidocaine (use with caution) or isoproterenol. Avoid using antiarrhythmic agents that can prolong QT interval (e.g. class IA or III agents). Correct electrolyte abnormalities and acid-base balance. IV fluids and vasopressors may be used to manage hypotension; phenylephrine, levarterenol or metaraminol may be appropriate for the management of refractory hypotension. May administer diphenhydramine HCl or benztropine mesylate in case of acute extrapyramidal symptoms. Consider performing gastric lavage and repeated doses of activated charcoal.
Drug Interactions
May potentiate CNS depressant effect of opioids, anaesthetics, barbiturates, narcotics or other psychoactive drugs.
Potentially Fatal: Increased thioridazine levels with CYP2D6 inhibitors (e.g. fluoxetine, paroxetine), fluvoxamine, propranolol and pindolol resulting to increased risk of cardiac arrhythmias and Torsades de pointes. May exacerbate cardiotoxic effects with QT prolonging drugs (e.g. disopyramide, procainamide).
Food Interaction
May enhance the CNS depressant effect of alcohol.
Lab Interference
May cause false-positive result with urine detection of methadone and phencyclidine.
Action
Description: Thioridazine is a piperidine phenothiazine that blocks postsynaptic mesolimbic dopaminergic receptors in the brain. It also has activity at serotonin, noradrenaline and histamine receptors.
Pharmacokinetics:
Absorption: Rapidly absorbed. Bioavailability: 25-33%. Time to peak plasma concentration: Approx 1-4 hours.
Distribution: Crosses placenta and enters the breast milk. Volume of distribution: 1.8-6.7 L/kg. Plasma protein binding: 96-99.3%.
Metabolism: Metabolised by CYP2D6 via sulphoxidation, demethylation and hydroxylation to mesoridazine (main active metabolite) and sulforidazine.
Excretion: Elimination half-life: 5-27 hours.
Chemical Structure

Chemical Structure Image
Thioridazine

Source: National Center for Biotechnology Information. PubChem Database. Thioridazine, CID=5452, https://pubchem.ncbi.nlm.nih.gov/compound/Thioridazine (accessed on Jan. 23, 2020)

Storage
Store between 20-25°C. Protect from light.
MIMS Class
ATC Classification
N05AC02 - thioridazine ; Belongs to the class of phenothiazine antipsychotics with piperidine structure.
References
Anon. Thioridazine. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 22/07/2020.

Anon. Thioridazine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 09/07/2020.

Buckingham R (ed). Thioridazine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 09/07/2020.

Ridazine (Atlantic Lab). MIMS Thailand. http://www.mims.com/thailand. Accessed 09/07/2020.

Thioridazine Hydrochloride Tablet, Film Coated (Mylan Institutional Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 09/07/2020.

Disclaimer: This information is independently developed by MIMS based on Thioridazine from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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