Why Do People Take Thyroid Replacement?
Many people take thyroid replacement therapy for conditions such as Hashimoto’s disease, post-thyroidectomy for thyroid cancer, Grave’s disease, or during pregnancy due to increased thyroid hormone requirements. The hormone given is T4, known as thyroxine, and levothyroxine is a blanket term for the different types of synthetic thyroxine.
Thyroxine Formulations in Australia
In Australia, there are four main formulations of thyroxine available:
- Oroxine and Eutroxsig: These need to be stored in the fridge.
- Eltroxin and Levoxine: These can be stored outside the fridge but at temperatures below 25 degrees Celsius.
These formulations are bioequivalent, meaning 50mcg of one is the same as 50mcg of the other, except for Eltroxin, which is slightly lower in strength. Therefore, you might need a slightly higher dose if switching to Eltroxin.
Storage and Stability
Eltroxin and Levoxine lose stability at temperatures higher than 25 degrees, so they still need to be kept in a cool place. If someone suddenly becomes hypothyroid despite being stable on the same thyroxine dose for a long time, it is likely that the box of thyroxine is damaged. Instead of increasing the dose, it is better to start a new box and take it for at least a few weeks before re-checking TSH levels.
Similarly, if someone picks up the maximum of 200 tablets, which lasts several months, the efficacy may decrease by 3-5% towards the end of the box. If TSH is tested at that time, it might be slightly elevated.
Absorption Issues
Absorption is another big issue for thyroxine. For best absorption, it needs to be taken on an empty stomach 30-40 minutes before food, coffee, or other medications—everything but water. If people cannot remember to take it fasted, it’s best to do the same thing every day, such as taking it with food every day, to find a stable dose.
Impact of Mineral Supplements
Mineral supplements like iron, calcium, multivitamins, or pregnancy supplements will impair thyroxine absorption if taken within a few hours. It is recommended to wait at least three hours between taking these supplements and thyroxine, so it’s best to take them at another time of the day.
Addressing Persistent Hypothyroidism
If someone remains hypothyroid despite taking thyroxine, it’s important to screen how they take it, test for malabsorption (e.g., from celiac disease), or consider a lab assay issue.