The advantages of this regimen are that control is smoother and that clinic visits are required only every three to four months. The duration of the course of antithyroid drugs remains empirical but is usually for 1-1.5 years.
Some, but not all, reports suggest that the use of a blocking-replacement regimen, followed by a maintenance dose of T4 for a year or two, may enhance the likelihood of an immunological remission. In the UK, some sixty-five per cent of patients relapse within a year of antithyroid therapy, and even higher relapse rates are reported in North America. This result, combined with the greater frequency of drug side effects associated with higher drug dosage, has led to disenchantment with antithyroid drugs as the primary therapy in North America and hence to a much more widespread use of radioiodine therapy.
