Long term drug treatment

Antithyroid drugs are used in hyperthyroidism on the basis that the course may be self-limited, so suppression of the disease will tide the patient over until spontaneous remission occurs.

The treatment of choice is carbimazole - in the UK - or it's active metabolite - methimazole - in the USA. Propylthiouracil is an alternative.

Two regimens can be employed:

• block-replace – a higher dose of anti thyroid drug (ATD) is used with concurrent replacement with levothyroxine
• titrated – ATD is titrated over time to the lowest dose needed for maintaining a euthyroid state (1,2)

Remission rate for both regimens is around 50% in patients who continue the drugs between six and 18 months and then stop. In either regimen, patients may relapse once the treatment is stopped (1).

• due to the higher incidence of side-effects associated with block and replace regimen, titration regimen is recommended as the first line approach in patients with Graves’ (2)

The side effects and efficacies of antithyroid drugs are similar and one may be substituted for another since cross-sensitivity between them is uncommon. Carbimazole is secreted in breast milk and therefore breast feeding is contraindicated during treatment.

Reference:

• (1) Vaidya B, Pearce SH. Diagnosis and management of thyrotoxicosis. BMJ. 2014;349:g5128
• (2) De Leo S, Lee SY, Braverman LE. Hyperthyroidism. Lancet (London, England). 2016;388(10047):906-918.