Thyroxine stability and formulation: why the secrecy?
Jim Stockigt, Australian Prescriber
Clinical strategies in the testing of thyroid function
Jim Stockigt, Thyroid Manager
Editor, – In May 2004 Australian pharmacists were instructed that thyroxine tablets should be stored refrigerated, before and after dispensing. This uniquely Australian directive, which carried the imprimatur of Sigma, the sole supplier of thyroxine tablets in Australia, and the Therapeutic Goods Administration, appears to have been ill-considered. (1) Dampness should be avoided during storage of thyroxine (2); repeated daily opening of a refrigerated glass bottle over many months can make the tablets damp, with loss of potency. (1) Sigma has now conceded that tablets in current use from unsealed bottles should not be refrigerated (1), although pharmacists generally are unaware of this change.
In letters to doctors and pharmacists during 2005, Sigma foreshadowed a change in formulation so that thyroxine tablets will be presented in five bottles of 40 tablets, with a recommendation to refrigerate the unopened bottles, but not the bottle in current use. In support of this change, Sigma refers to ‘new stability data’. However, Sigma has refused to present these data for professional scrutiny, except under terms of a confidentiality agreement that precludes discussion or peer review.
The reasons for seeking public disclosure of these ‘new stability data’ have been set out in detail. The health of about 200 000 Australians depends on thyroid hormone replacement. They, and those who accept responsibility for prescribing this medication, have a right to know the details of the sole preparation that is available. If storage temperature is a key factor in maximising the tenuous shelf-life of thyroxine, our local data might be important in addressing the broader problems of stability, potency and bioavailability of thyroxine. (3, 4)
If we cannot achieve a culture of open disclosure between the pharmaceutical industry and consumers for a medication as straightforward as thyroxine, what chance do we have with medications that are shrouded in commercial confidentiality, contentious trial data, patent law and unexpected or contentious adverse effects? Do we really care whether there is an ethos of evidence-based medicine in the manufacturing, regulatory and dispensing arms of pharmaceutical practice? If so, the ‘new stability data’ should be made known. Only in that way can consumers establish whether the modified formulation is necessary, or whether it is being introduced as a face-saving initiative.
- Stockigt JR, Should thyroxine tablets be refrigerated? Have we got it wrong in Australia?, (with reply by Siddiqui O, Sigma Pharmaceuticals). Med J Aust 2005;182:650.
- Roberts GW, Taking care of thyroxine, Aust Prescr 2004;27:75-6.
- American Association of Clinical Endocrinologists (AACE), The Endocrine Society (TES) and American Thyroid Association (ATA), Joint position statement on the use and interchangeability of thyroxine products, American Thyroid Association; 2004.
- Stockigt J, Testing the bioavailability of oral L-thyroxine by studying its absorption: smoke or mirrors?, Thyroid 2004;14:167-8.