Long-Term Treatment with Antithyroid Drugs: Efficacy and Safety

Medical therapy of hyperthyroidism has been the Astwood’s gift to medicine. However, controversy remains about its mechanisms of action, the ideal treatment duration, and its proper use in pregnancy. The concept that hyperthyroidism could be controlled ‘indefinitely’ with antithyroid drugs (ATDs) is also a topic of current debate. The purpose of this review was to highlight the pros and cons of long-term ATD therapy.

 PubMed, Scopus, Web of Science, and Google Scholar databases were searched for retrieving studies conducted on long-term treatment with ATDs up to Jan 2020. The final selection of the papers was made based on their relevancy with the safety and efficacy of long-term treatment with ATDs.

The main drawback of the ATD treatment is the high relapse rate after drug discontinuation. On the other hand, ATDs may have a favorable immunosuppressive effect, either primarily, in the diminution of thyroid-specific autoimmunity, or secondarily, as a result of controlling the hyperthyroid state, hence keeping patients in a euthyroid state for a prolonged period to diminish autoimmunity and hyperthyroid relapse. This often calls for long-term use of methimazole, but with the lowest possible dose to minimize the risk of side effects. Emerging evidence demonstrates that the long-term treatment with ATDs has relatively few adverse events, most of which arise within the starting months of treatment and in subjects on larger doses. Hence, once we have reached the end of a conventional course of ATD treatment (12 - 18 months), the hazard is eliminated, and adverse events are very rare to occur. Therefore, by continuing low-dose ATD, we could safely maintain the patient’s euthyroid status.

Long-term ATD treatment is safe, especially at a low dose. It can be considered as the preferred treatment for selected hyperthyroid patients.