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Drugs and Thyroid interactions

Drugs which may modify thyroid physiology (normal functioning hormones and levothyroxine therapy)

Anticoagulants: heparin (Cirkan, Flaxiparin)
Oral hypoglycemic drugs: Metformin (Glucophage, Glucomin), Diamicron, Daonil
Hormones: androgens (Andractim, Androtardyl), insulin
Antihypertensive medications: beta blockers (Avlocardyl, Celectol, Tenormin, Sectral)
Antiarrythmic: amiodarone (Cordarone)
Anti-infection: sulfa (Bactrim), anti-tuberculosis (Rifadin), antifungal (Griseofulvin)
Psychotropic: phenitoine (Dilantin), barbiturate (phenobarbital – Gardenal), diazepam (Valium), moor regulator and analgesic (carbazepine – Tegretol), lithium (Teralithe)
Anti-Parkinson drugs: levodopa (Modopar)

Drugs which may modify the ratio with binding proteins

Estrogens in hormone replacement therapy and birth control pill
Non-steroidal anti-inflammatory: mefenamic acid (Ponstyl), phenylbutazone (Butazolidine)
Corticoids: prednisone (Cortancyl), prednisolone (Solupred), betamethasone (Celestone)
Psychotropic: perfenazine (Trilifan)
Tricyclic anti-depressant (with mutual potentiation of the effects): Elavil, Elatrol, Laroxyl, Tofranil, Anafranil
Anti-cancer drugs: tamoxifen (Novadex), asparaginase (Kidrolase), fluorouracil

Drugs leading to decreasing digestive absorption of levothyroxine

Gastro-intestinal drugs: aluminium salts sucralfate (Ulcar), aluminium hydroxide (Maalox, phosphalugel), metroclopramide (Anausin, Pramin), proton-pump inhibitors (Omeprazole, Mopral, Losec, Nexium)
Lipid-lowering drugs: bile acid sequestrant (cholestyramine – Questran), Colespitol
Iron
Calcium
Accelerator of the bowel movements (laxatives, purgatives), absorbents (coal, clay)

The difference between decreasing absorption and modification of the ratio with serum proteins is that the first occurs during digestion, the second occurs in the plasma.

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