Some patients may request combination thyroid hormone replacement therapy with levothyroxine (T4) and liothyronine (T3), including desiccated animal thyroid gland extract e.g. Armour Thyroid.
T3 is the active hormone derived from deiodination of T4. Levothyroxine is the standard form of thyroid hormone replacement and has a long half life which enables once daily dosing and stable plasma T4 levels. Liothyronine has a shorter half life and steady state levels cannot be achieved with once daily dosing.
Available T4/T3 combination therapies are unlicensed in the UK and safety and quality can therefore not be assured. Furthermore, preparations such as Armour Thyroid contain a non-physiological (high) ratio of T3:T4, which is potentially harmful. The only available licensed preparation of liothyronine in the UK contains 20 micrograms of T3 which does not facilitate physiological combination therapy in conjunction with T4. The Royal College of Physicians has previously published a position statement on the management of patients with hypothyroidism and endorsed the use of levothyroxine monotherapy for the treatment of hypothyroidism on the basis of overwhelming clinical evidence.1 The British Thyroid Association more recently undertook a systematic review of the treatment of hypothyroidism.2 Their findings did not support the routine use of T4/T3 combination therapy due to insufficient evidence from controlled clinical trials.
Liothyronine, either alone or in combination with levothyroxine, is not routinely recommended for the treatment of hypothyroidism. However, in patients already established on combination treatment, liothyronine should not be discontinued without prior discussion with the individual. Short term use of liothyronine remains appropriate in patients with thyroid cancer e.g. prior to radioactive iodine therapy. In patients with ongoing symptoms despite levothyroxine consideration should be given as to whether the original diagnosis was correct i.e. was TSH significantly elevated? Levothyroxine doses should be optimised by aiming for a TSH in the lower third of the normal reference range and consideration should be given to alternative causes of the patient’s symptoms eg fibromyalgia, depression or other autoimmune conditions. Liothyronine should only be initiated on the advice of an endocrinologist.
- Royal College of Physicians. The diagnosis and management of primary hypothyroidism. A statement made by the Royal College of Physicians on behalf of: The Association of Clinical Biochemistry, British Thyroid Foundation, Society for Endocrinology, British Thyroid Association, British Society of Paediatric Endocrinology and Diabetes; endorsed by the Royal College of General Practitioners. 2011.
- Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee. Clinical Endocrinology 2016;84:799-808.