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Indication & Dosage |
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| Oral |
| REPLACEMENT THERAPY IN HYPOTHYROIDISM |
| Adult:
Healthy adults <50 yr and those >50 yr who have been recently treated for hyperthyroidism or who have been hypothyroid for only a short time: 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. |
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| Oral |
| REPLACEMENT THERAPY IN HYPOTHYROIDISM |
| 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 quarter of the recommended dose and increase by quarter 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. |
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| Oral |
| SEVERE AND CHRONIC HYPOTHYROIDISM |
| Adult:
Initially, 12.5-50 mcg/day. Adjust dose in steps of 12.5-25 mcg at 4-wkly intervals. |
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| Oral |
| SEVERE AND CHRONIC HYPOTHYROIDISM |
| Child:
Initially, 25 mcg/day. Adjust dose by 25 mcg every 2-4 wk. |
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| Oral |
| 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. |
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| Intravenous |
| 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. |
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| Administration |
Should be taken on an empty stomach (i.e. At least one hour before food or four hours after food). (Take on an empty stomach ½-1 hr before meals.) |
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| 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. |
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Potentially Life-threatening
Adverse Drug Reactions |
Nervousness, excitability, tremor, muscle weakness, cramps; sweating, flushing, heat intolerance, headache, insomnia, tachycardia, palpitations, angina pectoris, excessive wt loss; menstrual irregularities; diarrhoea, vomiting. |
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| Adverse Drug Reactions |
Convulsions, cardiac arrhythmia, heart failure, coma. |
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| Interactions |
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. |
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