Thyroid Hormones

Levothyroxine sodium is the treatment of choice for maintenance therapy.

DO NOT PRESCRIBE LIOTHYRONINE ROUTINELY OR INITIATE IN PRIMARY CARE. TO BE USED IN EXCEPTIONAL CIRCUMSTANCES ONLY ON SPECIALIST ADVICE

Liothyronine sodium has a similar action to levothyroxine but is more rapidly metabolised and has a more rapid effect; 20 - 25 micrograms is equivalent to 100 micrograms of levothyroxine. It may be used in severe hypothyroid states when a rapid response is required. In view of its short duration of action it is usually administered two or three times a day.

Liothyronine injection

For hypothyroid (myxoedema) coma and in hypothyroidism where oral therapy not possible, IV levothyroxine is the first choice parenteral product. This is licensed for myxoedema coma and hypothyroidism where oral therapy is not appropriate/possible. 

For treatment of myxoedema coma:

• Urgent advice should be sought from an endocrinologist – follow local Trust guidelines.

For hypothyroidism where oral therapy not possible:

• Oral levothyroxine has a long half-life (approx. 7 days) and oral liothyronine is much shorter (1-2 days).
• Consider crushing tablets and mixing with water for patients with swallowing difficulties or enteral feeding tubes.
• Where no oral or enteral route is available, consider parenteral administration of IV levothyroxine after the following time frame:
  • Levothyroxine tablets – replace with levothyroxine injection if no enteral access after 7 days
  • Liothyronine tablets – replace with IV levothyroxine injection if no enteral access after 2 days.

For patients admitted with hypothyroid (myxoedema) coma, treatment should start immediately.

NOTE – Parenteral liothyronine may still be considered in some circumstances on specialist endocrinologist advice, subject to product availability.