Drug Safety update
May 2021: Levothyroxine: new prescribing advice for patients who experience symptoms on switching between different levothyroxine products
October 2018: Ritonavir-containing products: reports of interaction with levothyroxine leading to reduced thyroxine levels
Levothyroxine sodium is the treatment of choice for maintenance therapy. The initial dose should not exceed 100micrograms daily, preferably before breakfast, or 25 to 50 micrograms in elderly patients or those with cardiac disease, increased by 25 to 50 micrograms at intervals of at least 4 weeks.
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 may be required when a patient is nil by mouth for prolonged periods and to treat hypothyroid coma.
For patients that are nil by mouth:
- Levothyroxine has a reasonably long half-life (6-7 days), and liothyronine much shorter (1-2 days)
- If a patient becomes nil by mouth or has an unsafe swallow and no other enteral access is possible, (e.g. NGT/PEG) - then the switch to liothyronine injection can safely take place around the following time-frame:
- Levothyroxine: replace with liothyronine injection if no enteral access after 7 days
- Liothyronine: replace with liothyronine injection if no enteral access after 2 days
For patients admitted with hypothyroid (myxoedema) coma, treatment should begin immediately.
