Shifts in propylthiouracil and methimazole prescribing practices: Antithyroid drug use in the United States from 1991 to 2008

Context: The thionamide antithyroid drugs methimazole and propylthiouracil are the mainstay of pharmacologic therapy for Graves' disease. However, little is known about the rate of use of these drugs and the prescribing practices of physicians treating hyperthyroidism. Objective: The objective of the study was to examine the frequency of methimazole and propylthiouracil use from years 1991 to 2008. Methods: The data were acquired by the U.S. Food and Drug Administration's Division of Epidemiology through two databases: IMS National Sales Perspectives and the Surveillance Data, Inc. Vector One: National database. Results: There was a 9-fold increase in the annual number of methimazole prescriptions during the study period, from 158,000 to 1.36 million per year. There was a 19% increase in the annual number of propylthiouracil prescriptions, from 348,000 to 415,000 per year. Propylthiouracil, which held two thirds of the market from 1991 to 1995, was surpassed by methimazole in 1996. Patient demographic data indicated that although 72% of methimazole prescriptions were for females, males were more likely to be on methimazole (82%) than females (74%) (P < 0.001, two tailed χ² test). The only demographic group in which methimazole use decreased was women of child-bearing age (5% decrease, P < 0.001, two tailed χ²). The incidence of hyperthyroidism in 2008 was estimated based on the number of new prescriptions of thionamides by age group and data from the 2008 U.S. census: 0.44 per 1000 for ages 0-11 yr, 0.26 per 1000 for ages 12-17 yr, 0.59 per 1000 for ages 18-44 yr, 0.78 per 1000 for ages 45-64 yr, and 1.01 per 1000 for ages 65+ yr. Conclusions: Methimazole has become the most frequently prescribed antithyroid drug. The remarkable increase in the total number of dispensed thionamide prescriptions over the last 18 yr may indicate a trend toward pharmacological treatment as primary treatment of Graves' disease in the United States.