Changes to the shelf-life of thyroxine

Editor, – In June 2003 the Therapeutic Goods Administration (TGA) instructed Sigma Pharmaceuticals to reduce the shelf-lives of Oroxine and Eutroxsig - the Australian brands of thyroxine - from 24 months to 12 months (with refrigeration). This was in light of evidence that their potency was reduced at the end of their shelf-life. Sigma, following consultation with the TGA, has been able to extend the shelf-life of these products to 18 months (with refrigeration), with a maximum unrefrigerated period of 4 weeks (below 25°C).

While Thyroid Australia understands and appreciates the TGA's efforts to ensure the potency of thyroxine for the entirety of its shelf-life, we view the change to refrigeration as a retrograde step in the treatment of hypothyroidism in Australia.

We are concerned that this change could have a negative impact on compliance. In addition, it seems Australia is the only country where thyroxine tablets require refrigeration. In many countries the shelf-life unrefrigerated is much longer than 18 months. This leads Thyroid Australia to question the TGA's approach to remedying potency issues with thyroxine. Addressing the matter by introducing refrigeration places the burden on patients.

Due to thyroxine, hypothyroidism is a readily treatable condition. It enables affected individuals to lead very close to normal lives. This change moves hypothyroidism from a condition that can be easily lived with, to a condition that impinges upon everyday life. In particular, it places limits on travel and spontaneity. We hope that refrigeration is only an interim measure until a more viable long-term solution is found.

Gail Pascoe
President, Thyroid Australia
Melbourne

Dr Leonie Hunt, Assistant Secretary, Drug Safety & Evaluation Branch, Therapeutic Goods Administration, comments:

The Therapeutic Goods Administration has been working with the manufacturer and sponsors of thyroxine tablets to review the potency of the tablets throughout their shelf-life. There have been a number of consumer complaints about apparent lack of potency of thyroxine tablets over time. It is apparent that these tablets do not maintain their full potency if stored at room temperature.

For this reason it has been considered necessary to change recommended storage conditions of the tablets so they are now recommended to be stored in the refrigerator. It is essential that there be no significant variability in the potency of tablets either within any one bottle of tablets or between successive bottles of tablets. Refrigerated storage will assist in this endeavour.

The shelf-life of a medicine in any country will depend on a number of factors including the manufacturing within that country, room temperature conditions and factors related to the final formulation sold in the market place. What is important is that the shelf-life and storage conditions chosen for a market place result in the brands in that market place having reliable stability and potency over time.

Sigma Pharmaceuticals, the manufacturer of thyroxine tablets, did not wish to add to the discussion.