Liothyronine


Concise Prescribing Info
Indications/Uses
Listed in Dosage.
Dosage/Direction for Use
Adult : PO Hypothyroidism As replacement therapy: Initial: 5-25 mcg/day, may increase gradually every 1-2 weeks. Maintenance: 60-75 mcg/day in 2-3 divided doses. Max: 100 mcg/day. T3 suppression test 75-100 mcg/day for 7 days. IV Myxoedema coma 5-20 mcg, repeat 12 hourly if needed. Minimum interval between doses: 4 hours.
Dosage Details
Intravenous
Myxoedema coma
Adult: 5-20 mcg by slow inj. Repeat 12 hourly, as necessary. Minimum interval between doses: 4 hours. Alternatively, 50 mcg initially then 25 mcg 8 hourly; may reduce to 25 mcg bid.
Elderly: Initiate at the lower end of the dosing range.

Oral
Hypothyroidism
Adult: As replacement therapy: Initially, 5-25 mcg daily; increase slowly, in increments of up to 25 mcg daily every 1-2 weeks, to a maintenance of 60-75 mcg daily in 2-3 divided doses. Some patients may need up to 100 mcg daily. Patients with CV disorders: Initially, 5 mcg once daily; increase by 5 mcg daily every 2 weeks.
Child: Initially, 5 mcg once daily; increase by 5 mcg every 3-4 days based on clinical response and tolerability. Maintenance: <1 year 20 mcg daily; 1-3 year 50 mcg daily; >3 years Same as adult dose.
Elderly: Initially, 5 mcg once daily; increase by 5 mcg daily every 2 weeks.

Oral
T3 suppression test
Adult: 75-100 mcg once daily for 7 days.
Elderly: Initiate at the lower end of the dosing range.
Administration
May be taken with or without food.
Contraindications
Uncorrected adrenal insufficiency or untreated thyrotoxicosis, acute MI or angina of effort; artificial rewarming (IV).
Special Precautions
Patients with adrenal insufficiency, myxoedema, severe and long-standing hypothyroidism; diabetes mellitus or diabetes insipidus; CV disease including angina, coronary artery disease and hypertension. Renal impairment. Children and elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Osteoporosis, MI, poor glycaemic control.
Cardiac disorders: Angina, arrhythmia, cardiac failure, tachycardia.
Gastrointestinal disorders: Diarrhoea, abdominal cramps, vomiting.
General disorders and administration site conditions: Fever, heat intolerance.
Immune system disorders: Hypersensitivity including (e.g. angioedema, urticaria).
Injury, poisoning and procedural complications: Phlebitis.
Investigations: Weight loss.
Metabolism and nutrition disorders: Increased appetite.
Musculoskeletal and connective tissue disorders: Muscle weakness and cramps, twitching.
Nervous system disorders: Excitability, headache, tremors.
Psychiatric disorders: Anxiety, insomnia, nervousness, restlessness.
Reproductive system and breast disorders: Menstrual irregularities, impaired fertility.
Skin and subcutaneous tissue disorders: Excessive sweating, pruritus, rash, hair loss.
Vascular disorders: Flushing, hypotension, hypertension.
Potentially Fatal: Cardiopulmonary arrest.
IV/Parenteral/PO: A
MonitoringParameters
Monitor TSH and triiodothyronine (T3) levels periodically during therapy; signs of hypo- or hyperthyroidism. Monitor thyroid function test (FT4, T3, T4) every 1-2 days in patients with myxoedema coma. Monitor cardiac function including blood pressure, heart rate, electrical activity (ECG) and recent or aggravated cardiac symptoms (e.g. chest pain, palpitations) regularly. Obtain bone mineral density test especially in postmenopausal women.
Overdosage
Symptoms: Anxiety, heat intolerance, insomnia, irritability, menstrual irregularities, nervousness, palpitation, sweating, tachycardia, tremors, weight loss, angina, arrhythmia, acute myocardial infarction, CHF,  fever, shock (if with untreated pituitary or adrenocortical failure), convulsions, coma. Management: Reduce dose or withdraw therapy temporarily. Symptomatic and supportive treatment. May perform gastric lavage, induce emesis, administer activated charcoal and correct electrolyte and fluid imbalances. Administration of β-blocker for the treatment of increased sympathetic activity and anticonvulsants for severe cases may be considered.
Drug Interactions
Increases serum plasma concentration of phenytoin. Increases the effect of oral anticoagulants (e.g. coumarin, phenindione) and sympathomimetic agents (e.g. epinephrine). May decrease the serum concentration of cardiac glycosides (e.g. digoxin). Decreased gastrointestinal absorption with bile acid sequestrants (e.g. colestyramine, colestipol). Decreased serum plasma concentration with carbamazepine, phenytoin. Decreased effect with oral contraceptives amiodarone, sertraline. Enhanced metabolism if concurrently administered with barbiturates (e.g. phenobarbital), primidone and rifampicin. Enhances receptor sensitivity to catecholamines when concurrently administered with TCAs (e.g. amitriptyline) resulting in increased risk for toxicity such as cardiac arrhythmias. Increased risk of hypertension and tachycardia when concurrently administered with ketamine. May alter the requirements of antidiabetic drugs. Accelerates the metabolism of β-blockers (e.g. propranolol).
Lab Interference
May alter thyroid function tests.
Action
Description: Liothyronine is involved in increasing the basal metabolic rate of carbohydrates, fats and proteins; regulation and differentiation of cell growth. It acts on DNA by entering the cell followed by attaching itself to thyroid receptor proteins, resulting in a hormone nuclear receptor complex. This complex is then responsible in activating gene transcription while synthesising messenger RNA and cytoplasmic proteins.
Onset: 2-4 hours (IV).
Pharmacokinetics:
Absorption: Adequately absorbed (about 95%) from the gastrointestinal tract.
Distribution: Binds to thyroxine-binding globulin (TBG) and some extent to thyroxine-binding pre-albumin (TBPA) or albumin. Enters breast milk (low amounts).
Metabolism: Metabolised in the liver via deiodination into inactive di-iodothyronine and mono-iodothyronine; also via conjugation with glucuronides and sulfates into metabolites that undergo enterohepatic recirculation in the bile and gut.
Excretion: Mainly via urine; remainder via faeces. Elimination half-life: 1-2 days (euthyroidism).
Chemical Structure

Chemical Structure Image
Liothyronine_01

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 5920, Liothyronine. https://pubchem.ncbi.nlm.nih.gov/compound/Liothyronine. Accessed Oct. 26, 2020.

Storage
Tab: Store between 15-30°C. Solution for inj: Store between 2-8°C. Storage recommendations may vary among countries or individual products. Refer to specific product guidelines.
ATC Classification
H03AA02 - liothyronine sodium ; Belongs to the class of thyroid hormones.
References
Anon. Liothyronine Sodium. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 21/09/2020.

Anon. Liothyronine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 21/09/2020.

Buckingham R (ed). Liothyronine Sodium. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 21/09/2020.

Cytomel Tablet (Pfizer Laboratories Div Pfizer Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 21/09/2020.

Cytomel Tablets, For Oral Use (Pfizer Inc New York). U.S. FDA. https://www.fda.gov/. Accessed 21/09/2020.

Joint Formulary Committee. Liothyronine Sodium. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 21/09/2020.

Liothyronine Sodium Injection, Solution (X-GEN Pharmaceuticals, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 21/09/2020.

Liothyronine. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com/. Accessed 21/09/2020.

Disclaimer: This information is independently developed by MIMS based on Liothyronine 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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