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Levothyroxine (Synthroid, Levothroid, Levoxine)

Category:

  • Hormone

Description:

  • Synthetic thyroid hormone

Indications:

  • Hypothyroidism (including cretinism, myxedema, non-toxic goiter)

  • Pituitary TSH suppression (thyroid nodules, Hashimoto’s disease, multinodular goiter, thyroid cancer)

  • Thyrotoxicosis (with antithyroid drugs)

Contraindications:

  • Adrenal insufficiency, MI

  • Thryrotoxicosis, hypersensitivity

Precautions:

  • Pregnancy category A

  • Cardiovascular disease

  • Diabetes mellitus or insipidus

Adverse Reactions (Side Effects):

  • CNS: headache, insomnia, nervousness, tremors

  • CV: angina pectoris, cardiac arrest, cardiac dysrhythmias, palpitations, tachycardia

  • GI: diarrhea,  gastric intolerance, vomiting

  • GU: menstrual irregularities

  • MISC: fever, heat intolerance, sweating, weight loss, allergic skin reactions (rare)

Dosage:

Administered orally, intramuscularly, intravenously

Adult:            

  • Hypothyroidism: 

    • PO 50mcg daily to start, increase by 25-50mcg daily at intervals of 2-4 weeks, usual dose 100-200mcg daily as a single dose; 

    • use = < 25 mcg/day in patients with long-standing hypothyroidism if cardovascular impairment present; 

    • IM/IV 50% of oral dose

  • Myxedema: 

    • IV 200-500mcg 1 time, then 100-300mcg the next day as needed; 

    • resume oral therapy as soon as clinical situation stabilized

  • TSH suppression: 

    • PO larger amounts than needed for replacement are required; 

    • optimal dose determined by laboratory findings and clinical response

Child    

  • 0-6 months: PO 8-10 mcg/kg or 25-50mcg daily

  • 6-12 months: PO 6-8 mcg/kg or 50-75mcg daily

  • 1-5 years: PO 5-6 mcg/kg or 75-100mcg daily

  • 6-12 years: PO 4-5 mcg/kg or 100-150mcg daily

  • IM/IV 75% of oral dose

Drug interactions:

  • Bile sequestrants: reduced serum thyroid hormone concentrations

  • Carbamazepine, phenytoin, rifampin: increased elimination of thryroid hormones; possible increased requirement for thryroid hormone in hypothyroid patients

  • Oral anticoagulants: thryoid hormones increase catabolism of vitamin K-dependent clotting factors; an increase or decrease in clinical thyroid status will increase or decrease the hypoprothrombinemic response to oral anticoagulants

  • Theophylline: reduced serum theophylline concentrations with initiation of thyroid therapy

Special considerations:

  • Transient, partial hair loss may be experienced by children in the 1st few months of therapy

  • Take as a single daily dose, preferably before breakfast

 


The information contained here is an abbreviated summary. For more detailed and complete information, consult the manufacturer's product information sheets or standard textbooks

Source: Operational Medicine 2001,  Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300

This information is provided by The Brookside Associates.  The Brookside Associates, LLC. is a private organization, not affiliated with any governmental agency. The opinions presented here are those of the author and do not necessarily represent the opinions of the Brookside Associates or the Department of Defense. The presence of any advertising on these pages does not constitute an endorsement of that product or service by either the US Department of Defense or the Brookside Associates. All material presented here is unclassified.

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