Levothyroxine and liothyronine
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From MedlinePlus, U.S. National Library of Medicine
l-Thyroxine, l-Triiodothyronine
Dosing in kidney impairment
CONTRAINDICATIONS Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency, untreated thyrotoxicosis, and apparent hypersensitivity to any of their active or extraneous constituents. There is no well-documented evidence from the literature, however, of true allergic or idiosyncratic reactions to thyroid hormone.
Drug interactions
Check levothyroxine and liothyronine against a medication listLabel text (4 paragraphs)
Drug Interactions Oral Anticoagulants Thyroid hormones appear to increase catabolism of vitamin K-dependent clotting factors. If oral anticoagulants are also being given, compensatory increases in clotting factor synthesis are impaired. Patients stabilized on oral anticoagulants who are found to require thyroid replacement therapy should be watched very closely when thyroid is started. If a patient is truly hypothyroid, it is likely that a reduction in anticoagulant dosage will be required. No special precautions appear to be necessary when oral anticoagulant therapy is begun in a patient already stabilized on maintenance thyroid replacement therapy.
Insulin or Oral Hypoglycemics Initiating thyroid replacement therapy may cause increases in insulin or oral hypoglycemic requirements. The effects seen are poorly understood and depend upon a variety of factors such as dose and type of thyroid preparations and endocrine status of the patient. Patients receiving insulin or oral hypoglycemics should be closely watched during initiation of thyroid replacement therapy. Cholestyramine or Colestipol Cholestyramine or colestipol binds both levothyroxine (T4) and liothyronine (T3) in the intestine, thus impairing absorption of these thyroid hormones. In vitro studies indicate that the binding is not easily removed.
Therefore four to five hours should elapse between administration of cholestyramine or colestipol and thyroid hormones. Estrogen, Oral Contraceptives Estrogens tend to increase serum thyroxine-binding globulin (TBg). In a patient with a nonfunctioning thyroid gland who is receiving thyroid replacement therapy, free levothyroxine (T4) may be decreased when estrogens are started thus increasing thyroid requirements. However, if the patient's thyroid gland has sufficient function, the decreased free levothyroxine (T4) will result in a compensatory increase in levothyroxine (T4) output by the thyroid.
Therefore, patients without a functioning thyroid gland who are on thyroid replacement therapy may need to increase their thyroid dose if estrogens or estrogen-containing oral contraceptives are given.
Supplement interactions
Dietary supplement interactions
4 noted- Calcium carbonate supplements can interfere with the absorption of levothyroxine (Synthroid, Levoxyl, and others), a thyroid hormone used to treat hypothyroidism and thyroid cancer. The FDA-approved label for this medication instructs patients who are taking calcium carbonate supplements to avoid taking levothyroxine within 4 hours of taking the supplement.
- Levothyroxine (Levothroid, Levoxyl, Synthroid, Tirosint, and Unithroid) is used to treat hypothyroidism, goiter, and thyroid cancer. The labels for some of these products warn that iron supplements can reduce the absorption of levothyroxine tablets and advise against administering levothyroxine within 4 hours of iron supplements.
- A small study found that taking chromium picolinate supplements at the same time as levothyroxine (used to treat hypothyroidism) decreases levothyroxine absorption over 6 hours.
- Ashwagandha might interact with thyroid hormone medications, a suggestion based on case reports of thyrotoxicosis.
Contraindications
Thyroid hormone preparations are generally contraindicated in patients with diagnosed but as yet uncorrected adrenal cortical insufficiency, untreated thyrotoxicosis, and apparent hypersensitivity to any of their active or extraneous constituents. There is no well-documented evidence from the literature, however, of true allergic or idiosyncratic reactions to thyroid hormone.
Safety data
Reported adverse events (FAERS)
Liver injury (LiverTox)
LiverTox has no chapter for levothyroxine and liothyronine. Check the label's hepatic warnings.
Pregnancy and lactation
Pregnancy
Pregnancy Thyroid hormones do not readily cross the placental barrier. The clinical experience to date does not indicate any adverse effect on fetuses when thyroid hormones are administered to pregnant women. On the basis of current knowledge, thyroid replacement therapy to hypothyroid women should not be discontinued during pregnancy.
Lactation
Nursing Mothers Minimal amounts of thyroid hormones are excreted in human milk. Thyroid is not associated with serious adverse reactions and does not have a known tumorigenic potential. However, caution should be exercised when thyroid is administered to a nursing woman.
For breastfeeding, also see LactMed (National Library of Medicine), which summarizes milk levels and infant effects.
Supply and cost
Drug shortage status
Recalls (last 24 months)
Therapeutic equivalence (Orange Book)
Price ladder
Not the price at the counterThese are not what a patient pays at the pharmacy counter. They are what pharmacies, health plans, and government buyers pay, before manufacturer rebates. A patient's cost depends on their insurance (copay, coinsurance, or deductible) or the pharmacy's cash price.