Hypothyroidism - Treatment

Drug Interactions with Levothyroxine. Many substances and conditions interact with levothyroxine and may either enhance or interfere with its absorption. Large amounts of dietary fiber may also reduce its action. People whose diets are consistently high in fiber may require larger doses of the drug. Since thyroid hormones regulate the metabolism and can affect the actions of a number of medications, dosages may need to be adjusted if a patient is being treated for other conditions. Even changing thyroxine brands can have a different effect.

Examples of Drug Interactions with Thyroid Hormone
Drugs that Inhibit Thyroid Hormone	Drugs that are Enhanced by Thyroid Hormone	Drugs that are Suppressed by Thyroid Hormone	Drugs that Reduce Natural Thyroid Hormone Levels and May Cause Hypothyroidism
Iron supplements (even low doses found in multivitamins). Calcium carbonate supplements. Aluminum-containing antacids (e.g., Maalox). Drugs used to reduce cholesterol levels by binding bile acids. Include colestipol (Colestid) and cholestyramine (Questran). Take four to five hours apart. Estrogens in oral contraceptives and hormone replacement therapy. May need to increase thyroid hormone while taking estrogen. Need to monitor thyroid after withdrawal from estrogen. Raloxifene (Evista), a designer-estrogen used for osteoporosis. (Evidence suggests interaction is weak.) Sucralfate (Carafate). Take at least two hours apart.	Epinephrine (adrenaline) injections. Thyroid hormone may increase the risk of serious side effects in heart disease patients given this agent. Warfarin, a blood thinner. Doses of this medication may need to be reduced if thyroid treatment is started after blood thinning treatments have begun. Many antidepressants. In some cases, potency of both antidepressants and thyroid hormones may increase.	Diabetic Drugs. Diabetic patients taking thyroid hormone may need additional insulin or oral hypoglycemic drugs. Stopping or reducing thyroid hormone may increase the risk of hypoglycemia. Digoxin. Patients with heart disease may need to increase their dosage of digoxin (Lanoxin).	Lithium. This drug, used in bipolar disorders, has multiple effects on thyroid hormone synthesis and secretion. Amiodarone (Cordarone). This drug, used to treat abnormal heart rhythms, contains iodine and can induce hyper- or hypothyroidism, particularly in patients with an existing thyroid problem. Antiseizure drugs used for epilepsy, including phenytoin and carbamazepine. Interferons and interleukins used in hepatitis, multiple sclerosis, and other conditions. Drugs increase thyroid auto-antibodies. Rifampin, used for tuberculosis. Some drugs used for cancer chemotherapy. Interferon. Large doses of selenium, a common over-the-counter supplement.