2. Food increases the absorption of thyroxine tablets. Answers to self-test questions 1. False 2. False First published online.
If you are taking thyroid hormone (eg. levothyroxine) for hypothyroidism or for a goitre (an enlarged thyroid gland) there is no need to supplement with iodine. It will do no good.
Iron supplements (FEOSOL, SLOW FE) have been shown to reduce the effect of levothyroxine in some people, although the effect is highly variable from one person to another. Other iron preparations may also have similar effects.
Conversely, a person whose thyroid function is too low will not respond normally to the anticoagulant, will be somewhat warfarin-resistant, and the blood will not be thin enough, that is, will clot too easily.
Question Can levothyroxine be taken with food, vitamins, iron, or other minerals? Answer Thyroid supplements should not be taken with food, vitamins, iron, or other minerals, but due to different reasons.
Drug interactions Most drug interactions are seen during shifts to and from the euthyroid state and rarely have any clinical significance during periods of thyroid stability. The hyperthyroid state increases clearance of some hepatically cleared drugs, notably propranolol, metoprolol and theophylline.
This is reduced to 34 days in hyperthyroidism and prolonged to 910 days in hypothyroidism. Thyroxine has a full therapeutic effect 34 weeks after starting treatment and will continue to have a therapeutic action for 13 weeks after treatment stops.
Consult your physician for diagnosis and treatment of your medical condition. The information provided is not a substitute for medical advice. Advances in medicine may cause this information to become outdated, invalid or subject to debate.
Interactions that result in changes of levothyroxine binding in blood Thyroxine-binding globulin (TBG) is a protein that binds to and carries thyroid hormone in the bloodstream. When the level of TBG is high, levothyroxine is trapped in the bloodstream and cannot get into the tissues where it is needed.
Antacids, iron salts, calcium carbonate (milk sucralfate, cholestyramine and soy-based formulas reduce the absorption of thyroxine. Conclusion There are significant stability, absorption and drug interaction issues surrounding the use of thyroxine.
Other drugs that may increase elimination of thyroid hormone include imatinib (GLEEVEC which is used to treat leukemia and other cancers and may result in hypothyroidism when used together with levothyroxine.
When the hypothyroidism is corrected by the levothyroxine the warfarin response returns to normal and the blood becomes too thin; life threatening bleeding has occurred from this series of events. In order to avoid such harmful interactions, patients need to know that their thyroid status can affect their warfarin requirements.
But those who are first on warfarin and then later start on levothyroxine run the risk of a magnified effect of warfarin, which can result in dangerous bleeding. In this case, the patient is likely to already be on a large dose of warfarin because the hypothyroidism has rendered them somewhat warfarin-resistant.
Gregory W. Roberts, Clinical Pharmacist, Repatriation General Hospital, Daw Park, South Australia. Summary Some of the pharmaceutical properties of thyroxine have important implications for the quality use of medicines. The stability of thyroxine tablets is limited and they may reach the expiry date before the bottle is finished.
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Following are several categories of enzyme inducers that can lower blood thyroid levels: Antiepileptic drugs used to treat seizures including carbamazepine (TEGRETOL oxcarbazepine (TRILEPTAL phenobarbital (LUMINAL, SOLFOTON primidone (MYSOLINE and phenytoin (DILANTIN ) can increase the metabolism of levothyroxine and would require larger doses of the drug.
If you take calcium, make sure there's at least four hours between taking the two kinds of medications. Be sure to notify your doctor or pharmacist regarding any prescription, over-the-counter or herbal medicines you are taking.