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Indications and Dosage
Oral
Hypothyroidism Adult: As replacement or supplemental therapy: Initially, 30 mg daily, increase by 15 mg increments every 2-3 weeks according to response. Maintenance dose: 60-120 mg daily. Oral Congenital hypothyroidism Child: ≤6 months 4.8-6 mg/kg daily. 6-12 months 3.6-4.8 mg/kg daily. 1-5 years 3-3.6 mg/kg daily. 6-12 years 2.4-3 mg/kg daily. >12 years 1.2-1.8 mg/kg daily.
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Special Patient Group
Patient with long-standing myxedema or CV diseases: Initially, 15 mg daily.
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Contraindications
Untreated thyrotoxicosis, uncorrected adrenal cortical insufficiency.
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Special Precautions
Patient with adrenal insufficiency, angina pectoris and other CV diseases, diabetes mellitus/insipidus, myxedema. Children. Pregnancy and lactation.
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Adverse Reactions
Significant: Exacerbation of adrenal insufficiency, diabetes mellitus/insipidus, myxedema, coronary artery disease.
Cardiac disorders: Cardiac arrhythmia, palpitations, tachycardia. Gastrointestinal disorders: Abdominal cramps, diarrhoea, constipation, vomiting. General disorders and administration site conditions: Fever. Investigations: Weight loss. Metabolism and nutrition disorders: Increased appetite. Musculoskeletal and connective tissue disorders: Chest pain, myalgia. Nervous system disorders: Ataxia, headache, heat intolerance, insomnia, nervousness, tremors, tremor of hands. Reproductive system and breast disorders: Menstrual disease. Skin and subcutaneous tissue disorders: Alopecia, diaphoresis. |
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Monitoring Parameters
Monitor TSH, heart rate, blood pressure; signs and symptoms of hypo/hyperthyroidism periodically.
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Overdosage
Symptoms: Hypermetabolic state. Management: Symptomatic and supportive treatment. May induce vomiting to suppress gastrointestinal absorption. Administer oxygen and maintain ventilation. May give glycosides if CHF develops; propranolol to treat increased sympathetic activities; cholestyramine to interfere with thyroxine absorption; and glucocorticoids to inhibit conversion of T4 to T3. Control fever, hypoglycaemia and fluid loss as needed.
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Drug Interactions
May diminish therapeutic effect of Na iodide. Increased risk of bleeding with vitamin K antagonists (e.g. warfarin). May increase plasma concentration of theophylline; may cause theophylline toxicity. May enhance the arrhythmogenic effect of tricyclic antidepressants. Decreased plasma concentration with bile acid sequestrants (e.g. colestipol, colestyramine) and oral contraceptives (e.g. estrogen). May decrease plasma concentration of digoxin. May cause hypothyroidism when given with amiodarone. May increase need for oral hypoglycemics or insulin.
Potentially Fatal: May cause serious toxic effects with sympathomimetic amines used for anorectic effect (e.g. phentermine). |
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Food Interaction
Decreased absorption with food, soybean infant formula, cottonseed meal, walnuts and dietary fibre.
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Action
Description: Thyroid is a natural product derived from porcine thyroid glands. It provides variable amounts of levothyroxine (T4) and liothyroxine (T3) hormones. The exact mechanism of action has not been fully elucidated, but it is known to enhance oxygen consumption by tissues, increase basal metabolic rate and metabolism of carbohydrate, lipids and proteins.
Synonym: dry thyroid, thyroid extract, thyroid gland, desiccated thyroid. Onset: Approx 3 hours (T3). Pharmacokinetics: Absorption: Absorbed from the gastrointestinal tract. Decreased absorption with food. Time to peak plasma concentration: 2-4 hours (T4); 2-3 days (T3). Distribution: Minimal amount crosses the placenta and enters breast milk. Plasma protein binding: >99% (T4) to plasma proteins including thyroxine-binding globulin, thyroxine-binding pre-albumin and albumin. Metabolism: Undergoes hepatic metabolism via outer ring deiodination by D1 (type 1 iodothyronine deiodinase) and converted to triiodothyronine (T3). Approx 80% T4 deiodinated in kidney and periphery. Glucuronidation and sulfation also occurs; undergoes enterohepatic recirculation. Excretion: Mainly via urine; partially faeces. Elimination half-life: T4: 9-10 days (hypothyroid); 6-7 days (euthyroid); 3-4 days (hyperthyroid). T3: 0.75 days. |
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Storage
Store between 15-30°C. Protect from light and moisture.
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MIMS Class
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ATC Classification
H03AA05 - thyroid gland preparations ; Belongs to the class of thyroid hormones.
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References
Anon. Thyroid, Desiccated. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 09/05/2018. Anon. Thyroid. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com/. Accessed 09/05/2018. Armour Thyroid, Porcine Tablet (Allergan, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 09/05/2018. Buckingham R (ed). Thyroid. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 09/05/2018. Nature Thyroid Tablet (PD-Rx Pharmaceuticals, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 09/05/2018. Preston CL (ed). Interactions of Thyroid Hormones. Stockley’s Drug Interactions [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 18/05/2018.
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