The United States Food and Drug Administration (FDA) has added a Boxed Warning to the label for propylthiouracil, a drug used to treat hyperthyroidism (overactive thyroid), to include information about reports of severe liver injury and acute liver failure, some of which have been fatal, in adult and pediatric patients using this medication.
The new warning also states that for patients being started on treatment for hyperthyroidism it may be appropriate to reserve use of propylthiouracil for those who cannot tolerate other treatments such as methimazole, radioactive iodine or surgery. In addition, due to the occurrence of birth defects that have been observed with the use of methimazole during the first trimester of pregnancy (see Data Summary), propylthiouracil may be the treatment of choice during and just before the first trimester of pregnancy.
Propylthiouracil has been shown to be effective in reducing thyroid hormone levels and decreasing symptoms associated with hyperthyroidism. However, to help patients understand the known benefits and potential risks of this medication, as part of a Risk Evaluation and Mitigation Strategy (REMS), FDA is requiring that a Medication Guide be given to every patient filling a prescription for propylthiouracil.
The recommendations in the Boxed Warning and the requirement of a Medication Guide are based on FDA's review of post-marketing safety reports of propylthiouracil (see Data Summary) as well as meetings with the American Thyroid Association, the National Institute of Child Health and Human Development, and the pediatric endocrine clinical community.