Exotis ISSN 2398-2985

Reptiles

Levothyroxine

Synonym(s): T4, L-thyroxine

Contributor(s): Vetstream Ltd, David Perpinan

Introduction

Name

  • Levothyroxine.
  • Levothyroxine sodium.

Class of drug

  • Synthetic hormone.

Description

Chemical name

  • (S)-2-Amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoic acid.

Molecular formula

  • C15H11I4NO4.

Molecular weight

  • 776.87.

Physical properties

  • Odorless, light yellow to buff-colored, tasteless, hygroscopic powder that is very slightly soluble in water and slightly soluble in alcohol.
  • Levothyroxine sodium is unstable in aqueous solutions. If using a commercial liquid preparations, it is suggested to obtain validated stability data for the product. 

Storage requirements

  • Store at room temperature in tight, light-resistant containers.
  • The injectable product should be reconstituted immediately before use and any unused product  should be discarded after reconstitution.

Uses

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Indications

  • Used to treat hypothyroidism, either primary or secondary: iatrogenic hypothyroidism may occur after thyroid gland removal.
  • Anecdotal reports of its use to treat hepatic lipidosis.

Administration

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Pharmacokinetics

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Precautions

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Interactions

with other drugs

Catecholamines
  • Epinephrine Epinephrine, norepinephrine.
  • Effects are enhanced by thyroxine.
Sympathomimetics
  • Effects are enhanced by thyroxine.
Warfarin
  • Potentiate the anticoagulant effects of warfarin by increasing the catabolism of vitamin K-dependent clotting factors.
Insulin
  • Diabetic patients may have altered insulin requirements - monitor carefully during the initiation of therapy.
Estrogens
  • May increase thyroid requirements by increasing TBg Estradiol.
Digoxin, digitoxin
  • The therapeutic effect may be reduced by thyroid hormones.
Ketamine
  • Increased risk of tachycardia and hypertension Ketamine.

With diagnostic tests

  • Many drugs (in humans) may have effects on thyroid function tests, including anabolic steroids, antithyroid drugs, barbiturates, corticosteroids, diazepam, fluorouracil, heparin, insulin, mitotane (op-DDD), nitroprusside, oestrogens, phenylbutazone, phenytoin, propranolol, salicylates and thiazides.

Adverse Reactions

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hadfield C A, Clayton L A, Clancy M M et al (2012) Proliferative thyroid lesions in three diplodactylid geckos: Nephrurus amyae, Nephrurus levis and Oedura marmorata. J Zoo Wildl Med 43 (1), 131-140 PubMed.

Other sources of information

  • Plumb D C (2015) Plumb's Veterinary Drug Handbook. 8th edn. Wiley-Blackwell, USA. pp 1296.
  • McArthur S, Wilkinson R & Meyer J (2004) Medicine and Surgery of Tortoises and Turtles. Blackwell Publishing, UK. pp 579.
  • Girling S J & Raiti P (2004) BSAVA Manual of Reptiles. BSAVA, UK. pp 383.
  • Tennant B (1999) Small Animal Formulary. 3rd edn. BSAVA, UK.

Organisation(s)

  • National Office of Animal Health (NOAH) Compendium of Data Sheets for Animal Medicines. Website: www.noahcompendium.co.uk.

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