Liothyronine

Liothyronine has a similar action to levothyroxine but has a more rapid effect and is more rapidly metabolised. Its effects develop after a few hours and disappear within 1–2 days of discontinuing treatment. It is available both as a tablet for oral administration and as a solution for slow intravenous injection. It is useful in severe hypothyroid states when a rapid response is desired. If adverse effects occur due to excessive dosage, withhold for 1–2 days and restart at a lower dose.The injectable form is useful in patients unable to absorb enterally.

Uses
Replacement for those unable to absorb enterally
Hypothyroid states, including coma

Contraindications
Thyrotoxicosis

Administration
Hypothyroid coma: 5–20 μg (neat or diluted in 5 ml WFI), given by slow IV over 5 min, 12 hourly. Give concurrent hydrocortisone 100mg IV, 8 hourly, especially if pituitary hypothyroidism suspected. Replacement for those unable to absorb enterally: 5–20 μg (neat or diluted in 5 ml WFI), given by slow IV over 5 min, 12 hourly, depending on the normal dose of levothyroxine.

Equivalent dose:

Oral levothyroxine (ug/day)	IV liothyronine (ug/12h)
200	20
150	15
100	10
50	5

Monitor:

ECG before and during treatment

TSH (T3 and T4 may be unreliable in the critically ill)

Normal range:TSH 0.5–5.7 mU/l,T3 1.2–3.0 nmol/l,T4 70–140 nmol/l

How not to use liothyronine

Rapid IV bolus

Adverse effects

Tachycardia

Arrhythmias

Angina

Muscle cramps

Restlessness

Tremors

Cautions

Panhypopituitarism or predisposition to adrenal insufficiency (give hydrocortisone before liothyronine)

IHD (may worsen ischaemia)