levothyroxine sodium, Synthroid, Levoxyl, Levothroid, Unithroid, Tirosint, Levo-T

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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GENERIC AVAILABLE: Yes. Generic and branded tablets of levothyroxine may differ:

  • in the amount of levothyroxine they contain,
  • the absorption of the levothyroxine into the body, and
  • the distribution of levothyroxine throughout the body.

This means that ingestion of 1 mg of generic levothyroxine may not have the same effect on the body as 1 mg of another generic or branded levothyroxine. Practically speaking, this means that when changing between levothyroxine manufactured by different pharmaceutical companies, a change in dose may be necessary to maintain the desired effect or to prevent toxicity. When switching between brands or generics, it is important to ensure that both preparations are equivalent or to check blood thyroid levels weekly.

PRESCRIPTION: Yes.

PREPARATIONS:

  • Tablets: 0.025, 0.05, 0.075, 0.088, 0.1, 0.112, 0.125, 0.137, 0.15, 0.175, 0.2 and 0.3 mg.
  • Capsules: 0.013, 0.025, 0.05, 0.075, 0.088, 0.1, 0.125 and 0.15 mg.
  • Powder for intravenous injection: 200 mcg and 500 mcg per vial.

STORAGE: Levothyroxine tablets, capsules, and dry powder should be kept at room temperature, 15 C to 30 C (59 F to 86 F) in a light-resistant, tight container.

Powdered levothyroxine for intravenous injection should be used immediately once mixed with liquid.

DOSING: For adult hypothyroidism, levothyroxine is started at 12.5-125 mcg/day administered orally. Starting doses and dose changes may differ with individual patients based upon age, the presence of cardiovascular disease, the development of tolerance (reduced effectiveness with continued use), side effects to the medication, and blood levels of thyroid hormone. It may take one to three weeks after initiating therapy with levothyroxine or changing the dose before effects are seen. The goal of replacement therapy is to maintain a normal blood thyroxine level.

DRUG INTERACTIONS: Initiation or discontinuation of therapy with levothyroxine in diabetic patients may create a need for an increase or decrease in the required dose of insulin and/or antidiabetic drug, (for example, glyburide [Micronase]).

Levothyroxine may increase the effect of blood thinners such as warfarin (Coumadin). Therefore, monitoring of blood clotting is necessary, and a decrease in the dose of warfarin may be necessary.

Medically Reviewed by a Doctor on 12/11/2014
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