Thioridazine

Oral
Schizophrenia

Lower initial dose and more gradual dosage increase.

Lower initial dose and more gradual dosage increase.

Should be taken with food.

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.

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.

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.

PO: C

This drug may impair physical and mental abilities, if affected, do not drive or operate machinery.

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/HbA_1c 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.

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.

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).

May enhance the CNS depressant effect of alcohol.

May cause false-positive result with urine detection of methadone and phencyclidine.

Description:
Mechanism of Action: 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.

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

Store between 20-25°C. Protect from light.

Antipsychotics

N05AC02 - thioridazine ; Belongs to the class of phenothiazine antipsychotics with piperidine structure.

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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.