Levothyroxine Sodium

Replacement therapy in hypothyroidism
Adult: Initially, 50-100 mcg daily, may increase by 25-50 mcg at 4-wkly intervals until the thyroid deficiency is corrected. Usual maintenance dose: 100-200 mcg daily. Patient should be evaluated every 6-8 wk to monitor response. Initiate with lower doses at 25-50 mg daily in patients >50 yr or patients <60 yr with underlying CV disease. Lower initial doses may be considered in patients with subclinical hypothyroidism if treatment is considered necessary.
Child: Neonates: Initially, 10-15 mcg/kg/day. Neonates at risk for cardiac failure: Consider lower doses of 25 mcg/day. Neonates with thyroxine levels <5 mcg/dl: Initially, 50 mcg/day. Adjust dose every 4-6 wk. Infants and children: Dose based on body wt and age: 0-3 mth: 10-15 mcg/kg/day; 3-6 mth: 8-10 mcg/kg/day; 6-12 mth: 6-8 mcg/kg/day; 1-5 yr: 5-6 mcg/kg/day; 6-12 yr: 4-5 mcg/kg/day; >12 yr: 2-3 mcg/kg/day. Older children: To minimise hyperactivity, initially ¼ of the recommended dose and increase by ¼ dose each wk until full replacement dose is reached. Children who have completed growth and puberty: Initially, 1.7 mcg/kg/day as a single dose. Titrate dose every 6 wk. Average initial dose: About 100 mcg; usual dose: ≤200 mcg/day; dose ≥300 mcg/day is rare and reevaluation should be prompted.
Elderly: >50 yr without cardiac disease or <50 yr with cardiac disease: Initially, 25-50 mcg/day. Adjust dose every 6-8 wk as needed. >50 yr with cardiac disease: Initially, 12.5-25 mcg/day. Adjust dose by 12.5-25 mcg increments every 4-6 wk. Elderly patients may require <1 mcg/kg/day.
Severe and chronic hypothyroidism
Adult: Initially, 12.5-50 mcg/day. Adjust dose in steps of 12.5-25 mcg at 4-wkly intervals.
Child: Initially, 25 mcg/day. Adjust dose by 25 mcg every 2-4 wk.
TSH suppression
Adult: For thyrotropin-dependent well-differentiated thyroid cancer: Doses >2 mcg/kg/day may be given as a single dose to suppress TSH to <0.1 MIU/L. For benign nodules and nontoxic multinodular goitre: Target TSH is generally higher at 0.1-0.5 MIU/L for nodules and 0.5-1.0 MIU/L for multinodular goitre.
Myxoedema coma
Adult: Initially, 200-500 mcg, followed by 100-300 mcg on the 2nd day if necessary, then 100-200 mcg daily until euthyroid state is achieved or the patient can tolerate oral admin. Patient with cardiac disease: Consider lower dose.
Elderly: Lower doses may be needed.
Untreated hyperthyroidism; uncorrected adrenal failure; recent MI.
Warnings / Precautions
Angina, heart failure; DM; diabetes insipidus; elderly; long-standing hypothyroidism; adrenal insufficiency; myxoedema. Do not use for treatment of obesity or for wt loss. Pregnancy, lactation.
Adverse Reactions
Nervousness, excitability, tremor, muscle weakness, cramps; sweating, flushing, heat intolerance, headache, insomnia, tachycardia, palpitations, angina pectoris, excessive wt loss; menstrual irregularities; diarrhoea, vomiting.
Potentially Fatal: Convulsions, cardiac arrhythmia, heart failure, coma.
Overdose Reactions
Chronic: Symptoms include hyperthyroidism, wt loss, nervousness, sweating, tachycardia, palpitations, insomnia, heat intolerance, menstrual irregularities, psychotic symptoms, fever, premature closure of epiphyses in infants. Reduce dose or withdraw therapy temporarily; general supportive care is advised. Acute: Symptoms include fever, hypoglycaemia, CHF, undiagnosed adrenal failure. Management is symptomatic and supportive; β-blockers (for massive overdose).
Drug Interactions
Reduced absorption with iron, colestyramine, colestipol, aluminium- and magnesium-containing antacids, calcium carbonate, simethicone, sucralfate. May alter requirements of antidiabetic drugs. Reduced efficacy of thyroid replacement therapy with imatinib. Reduced tri-iodothyronine serum levels with amiodarone. Reduced serum levels of thyroxine with carbamazepine, phenytoin, phenobarbital, rifampicin, oestrogens.
Potentially Fatal: Increased therapeutic and toxic effects of levothyroxine and TCAs. May change hypoprothrombinaemic response to warfarin and other oral anticoagulants (markedly increased response during replacement). Increased risk of significant hypertension and tachycardia with ketamine.
See Below for More levothyroxine sodium Drug Interactions
Lab Interactions
May alter thyroid function tests.
Food Interactions
Decreased bioavailability and lower serum levels of thyroxine with enteral nutrition. Reduced absorption with soybean infant formula, cottonseed meal, walnuts and dietary fibre.
Mechanism of Actions
Levothyroxine sodium increases the basal metabolic rate (BMR) of carbohydrates, fats and proteins. It is also involved in the regulation and differentiation of cell growth. These effects are mediated at the cellular level by the thyroxine metabolite, tri-iodothyronine.
Onset: Oral: 3-5 days; IV: 6-8 hr.
Absorption: Variable but adequate from the GI tract (oral); increased in fasting state.
Distribution: Crosses the placenta; enters breast milk. Protein-binding: Extensive to thyroxine-binding globulin.
Metabolism: Hepatic and renal; converted to liothyronine and inactive reverse triiodothyronine; undergoes enterohepatic recirculation.
Excretion: Via faeces. Half-life: 6-7 days (euthyroid); prolonged in hypothyroidism and reduced in hyperthyroidism.
Levothyroxine sodium: Should be taken on an empty stomach. (Take on an empty stomach ½-1 hr before meals.)
Storage Conditions
Intravenous: Store at 15-30°C (59-86°F). Oral: Store at 15-30°C (59-86°F).
ATC Classification
H03AA01 - levothyroxine sodium ; Belongs to the class of thyroid hormones.
Intravenous: Store at 15-30°C (59-86°F). Oral: Store at 15-30°C (59-86°F).
Available As
  • Levothyroxine Sodium 0.025 mg
  • Levothyroxine Sodium 0.037 mg
  • Levothyroxine Sodium 100 mcg
  • Levothyroxine Sodium 125 mcg
  • Levothyroxine Sodium 25 mcg
  • Levothyroxine Sodium 50 mcg
  • Levothyroxine Sodium 50 mg
  • Levothyroxine Sodium 75 mcg
  • Levothyroxine Sodium 80 mcg
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