Levothyroxine

Details About Generic Salt ::  Levothyroxine 

Main Medicine Class:: Endocrine,Steroid Hormones , Metabolic System   Sub Medicine Class ::  Thyroid , Anti Thyroid Drugs

8A. THYROID & ANTI-THYROID DRUGS in 8. ENDOCRINE/STEROID HORMONES & METABOLIC SYSTEM
LEVOTHYROXINE
SYNTHETIC THYROXINE HORMONE | THYROID HORMONE REPLACEMENT
PK: A: Variable M: Hepatic & renal E: Urine

Indications & Dose: HYPOTHYROIDISM PO Adult 100-125µg/day titrate dose q6wk, <50 yr with cardiac disease: Initially 25-50µg/day adjust dose by 12.5-25µg increments at 6-8 wk intervals as needed Child 0-3 month: 10-15µg/kg/day, use lower starting dose of 25µg/day if the infant is at risk for development of HF; if the initial serum T4 is very low (<5µg/dL) begin treatment at a higher dosage of 50µg/day, 3-6 months: 8-10µg/kg/day, 6-12 months: 6-8µg/kg/day, 1-5 yr: 5-6µg/kg/day, 6-12 yr: 4-5µg/kg/day, >12 yr: 2-3µg/kg/day, Growth & puberty complete: Same as adult dosing Elderly >50 yr without cardiac disease: Initially 25-50µg/day adjust dose by 12.5-25µg increments at 6-8 wk intervals as needed, >50 yr with cardiac disease: Initially 25-50µg/day adjust dose by 12.5-25µg increments at 4-6 wk interval | Severe PO Adult Initially 12.5-25µg/day, adjust dose by 25µg/day q2-4wks as appropriate Child Initially 25µg/day, adjust dose by 25µg q2-4wk | IV/IM Adult 50% of the oral dose Child 50% of the oral dose Elderly 50% of the oral dose | MYXEDEMA COMA IV Adult 200-500µg, then 100-300µg the next day if needed, small dose is required in patients with CVD Elderly Lower dose may be required | THYROID-STIMULATING HORMONE SUPPRESSION PO Adult Well-differentiated thyroid cancer: >2µg/kg/day to suppress TSH to <0.1 mIU/L in intermediate- to high-risk tumors. Low-risk tumors may be maintained at or slightly below the lower limit of normal (0.1-0.5 mIU/L)

Contra: Thyrotoxicosis, untreated hyperthyroidism

Precautions: CVD, hypopituitarism, predisposition to adrenal insufficiency, elderly, long-standing hypothyroidism, diabetes insipidus/DM, adrenal insufficiency without adequate corticosteroid cover

ADR: Serious: Anginal pain, arrhythmias, palpitations, tachycardia, skeletal muscle cramps, tremors, flushing, Others: sweating, excessive weight loss, muscular weakness, restlessness, excitability, insomnia, headache, diarrhea, vomiting

DDI: Serious Warfarin causes bleeding, Phenobarbital/Carbamazepine/Phenytoin/Rifampicin causes hypothyroidism, Amitriptyline enhances drug effects, Amiodarone increases the levels of thyroid-stimulating hormone/overt hypothyroidism, Ferrous Sulphate reduces drug effect, Calcium Carbonate reduces drug efficacy

Diet: Empty stomach (30 min before food)

Monitor: TFT, resin triiodothyronine uptake (rT3U), T4, TSH, HR, BP, clinical signs of hypo- and hyperthyroidism; cardiac overload, arrhythmias & aspiration from avid suckling (infants)