The antithyroid drugs propylthiouracil and methimazole are commonly used in the treatment of hyperthyroidism. The incidence of overall toxic drug reactions to these antithyroid drugs have been reported to vary from 6% to 9%1-3; however, the incidence of serious side effects, including agranulocytosis, is approximately 0.3% to 0.6% in a large series.4 Subsequent management of the hyperthyroidism in those patients who develop drug toxic reaction becomes a problem, especially in the younger age group where alternative forms of treatment are limited.