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L-thyroxine

Levothyroxine, also known as -thyroxine, is a synthetic form of the thyroid hormone thyroxine (T4). It is used to treat thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. It may also be used to treat and prevent certain types of thyroid tumors. It is not indicated for weight loss. Levothyroxine is taken orally (by mouth) or given by intravenous injection. Levothyroxine has a half-life of 7.5 days when taken daily, so about six weeks is required for it to reach a steady level in the blood.

Key facts

Drug.image: Levothyroxine 200.svg
Drug.image_class: skin-invert-image
Drug.image2: Levothyroxine-from-xtal-3D-bs-17.png
Drug.image_class2: bg-transparent
Drug.tradename: Synthroid, Levoxyl, others
Drug.MedlinePlus: a682461
Drug.DailyMedID: Levothyroxine
Drug.pregnancy_AU: A
Drug.routes_of_administration: By mouth, intravenous
Drug.ATC_prefix: H03
Drug.ATC_suffix: AA01
Drug.legal_AU: S4
Drug.legal_CA: Rx-only
Drug.legal_US: Rx only
Drug.bioavailability: 40-80%
Drug.metabolism: Mainly in the liver, kidneys, brain, and muscles
Drug.elimination_half life: ca. 7 days (in hyperthyroidism 3–4 days, in hypothyroidism 9–10 days)
Drug.excretion: Feces and urine

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Article

17 sections

Contents

Medical uses
50 and older
Pregnancy and breastfeeding
Children
Contraindications
Side effects
Interactions
Chemistry
Mechanism of action
Pharmacokinetics
History
Society and culture
Economics
Available forms
Research
References
External links

Side effects from excessive doses include weight loss, trouble tolerating heat, sweating, anxiety, trouble sleeping, tremor, and fast heart rate. Use is not recommended in people who have had a recent heart attack. Use during pregnancy has been found to be safe. Dosing should be based on regular measurements of thyroid-stimulating hormone (TSH) and T4 levels in the blood. Much of the effect of levothyroxine is following its conversion to triiodothyronine (T3).