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.