In short
Liothyronine sodium is a synthetic form of the thyroid hormone triiodothyronine (T3). It is being studied in a Phase 3 trial with 110 participants to see whether combining it with levothyroxine (T4) controls thyroid-stimulating hormone (TSH) better than levothyroxine alone in people with advanced thyroid cancer who are treated with tyrosine kinase inhibitors.
Key points
- Liothyronine sodium is a synthetic form of the natural thyroid hormone triiodothyronine (T3).
- One Phase 3 trial is studying liothyronine in advanced thyroid carcinoma and post-thyroidectomy hypothyroidism.
- The trial compares LT4 + LT3 combination therapy with levothyroxine (LT4) monotherapy.
- 110 participants are planned to be enrolled in the authorised trial.
- The main measure is the proportion of patients whose TSH stays within 0.1–4 mIU/L without dose adjustments.
- Liothyronine is given orally, as tablets or oral solutions.
What is liothyronine sodium?
Liothyronine sodium is the sodium salt of liothyronine, a synthetic form of the natural thyroid hormone triiodothyronine, also called T3. T3 is one of two main hormones produced by the human thyroid gland, alongside levothyroxine (T4). In the United Kingdom, liothyronine is listed in the NHS dictionary of medicines as a 10 micrograms/ml oral solution, classified under ATC code H03AA02. The prescribing status is recorded as valid as a prescribable product, with an oral route and oral solution form. Liothyronine sodium is not authorised as a medicine in the European Union trial record, but it is available in some countries as tablets or oral solutions.
How does liothyronine sodium work?
Liothyronine sodium replaces or supplements the body's own triiodothyronine (T3). T3 and T4 are produced in the thyroid gland by iodination and coupling of the amino acid tyrosine. T3 contains three iodine atoms and is formed by coupling one molecule of diiodotyrosine (DIT) with one molecule of monoiodotyrosine (MIT). Both hormones are stored in the thyroid colloid as thyroglobulin. In the body, T3 is the more active thyroid hormone. In people whose thyroid gland has been removed or is not working properly, taking liothyronine provides T3 directly. The clinical trial is testing whether adding T3 to standard T4 therapy helps keep TSH within a target range in people with advanced thyroid cancer.
Which conditions is it used or studied for?
- Advanced thyroid carcinoma — the trial studies people with advanced thyroid cancer who are starting treatment with tyrosine kinase inhibitors.
- Post-thyroidectomy hypothyroidism — after surgical removal of the thyroid gland, people may need thyroid hormone replacement, and the trial includes this condition.
How is liothyronine sodium given?
Liothyronine sodium is given by mouth. The NHS dictionary of medicines lists a 10 micrograms/ml oral solution, sugar free, as a valid prescribable product. The United States product information describes liothyronine sodium tablets. In the clinical trial, the study uses oral solutions at several strengths: Liotir 5 microgrammi/ml, Liotir 10 microgrammi/ml, Liotir 15 microgrammi/ml, Liotir 20 microgrammi/ml, and Liotir 20 microgrammi/ml oral drops. The trial also uses levothyroxine products as the comparison arm: EUTIROX 100 microgrammi tablets and LEVOTIRSOL 100 microgrammi oral solution.
What do the clinical trials show?
One Phase 3 trial is registered for liothyronine sodium in this dataset. The trial is authorised and plans to enrol 110 participants. It is a prospective, multicentre, randomised study. The main measure is the number and proportion of patients in each group who maintain TSH within the target range of 0.1–4 mIU/L throughout the study without any dose adjustments of LT4 and/or LT3. The study compares combined LT4 + LT3 therapy with LT4 monotherapy in controlling TSH in patients with advanced thyroid cancer after the start of systemic therapy with tyrosine kinase inhibitors.
What side effects are known?
According to the United States product information, liothyronine sodium belongs to the group of drugs with thyroid hormone activity. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given together with sympathomimetic amines such as those used for their anorectic effects. The same source notes that thyroid hormone drugs have been used for the treatment of obesity, but this is not an approved use for liothyronine sodium.