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6.2 Thyroid and antithyroid drugs

6.2.1 Thyroid Hormones

Levothyroxine sodium tablet
Liothyronine tablets, injection - see note


As Levothyroxine sodium has a long half-life (about 7 days), there is no reason to give it more often than once a day.

Full effects may not be seen for several weeks, and dosage adjustments should be made at 2-3 monthly intervals. Repeating thyroid function tests with a view to adjustment of replacement dosage any more frequently is inappropriate.

IV liothronine should be reserved for hypothyroid coma or for those patients who are not expected to take oral medication for several days. It will be used in combination with levothyroxine. See link to endocrinology statement.

In the elderly, and in patients with significant ischaemic heart disease or long-standing profound hypothyroidism, thyroid hormones should be commenced at a low dose and increased very cautiously, since angina and arrhythmias can be precipitated on starting treatment.

The effects of oral anticoagulants may be potentiated when thyroid hormones are started.


6.2.2 Antithyroid Drugs

Carbimazole tablets
Propylthiouracil tablets
Iodine solution aqueous ("Lugol's solution") R


Propranolol can help to control thyrotoxic symptoms (but has no effect on the underlying disease)

Both carbimazole and propylthiouracil may cause agranulocytosis. Patients should be warned to report unexplained fever, malaise or sore throat. Treatment should be stopped at once if there is clinical suspicion of neutropenia, until a blood count has been done.

Carbimazole and Propylthiouracil may cause allergic skin reactions. A change of agents may be appropriate with patients suffering sensitivity reactions to either drug.

Hyperthyroid patients are generally more sensitive to oral anticoagulants; increased dosage may be necessary as the hyperthroidism becomes controlled. Frequent review of INR is therefore recommended.

Specialist review of women on thyroid medication is recommended as early as possible in pregnancy.


For link to BNF section: 6.2 Thyroid and antithyroid drugs