Milk, calcium, iron, multivitamin supplements – may influence the absorption of levothyroxine.
For many years, two levothyroxine preparations have been marketed in Australia, Oroxine and Eutroxsig (both marketed by Aspen Pharmaceuticals), available in 50, 75, 100 and 200 microgram tablets. These preparations are identical, and so it has been immaterial which is dispensed to patients, and brand switching has not been problematic. A new preparation, Eltroxin (also marketed by Aspen) is now available which features a wider range of tablet strengths (25, 50, 75, 100, 125, and 200 microgram) and (unlike Oroxine/Eutroxsig) does not require refrigeration. This may allow more accurate daily dosing for patients and may be more convenient.[6] However, Eltroxin is not bioequivalent on a same dose basis with Eutroxsig/ Oroxine. If a decision is made to switch a patient from Eutroxsig/ Oroxine to Eltroxin, then prescribers should have a plan for monitoring TSH. Prescribers should be aware that dose adjustment may be required. Prescribers should tell their patients not to interchange Eltroxin and Eutroxsig/ Oroxine unless a decision has been made to switch products and there is a plan for monitoring TSH levels and review of dose. [1, 2, 6]
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