Discontinuing Antithyroid Drug Therapy before Ablation with Radioiodine in Graves Disease

15 October 1994 | Volume 121 Issue 8 | Pages 553-559

Objective: To determine the relative effects on thyroid hormone levels of discontinuing antithyroid drug therapy and subsequent ablation with radioiodine in patients with hyperthyroid Graves disease.

Design: A clinical trial with a prospective analysis of the relative change in thyroid hormone levels over time in response to therapy in two study groups.

Setting: An outpatient endocrine clinic at a tertiary care hospital.

Patients: 21 patients with a clinical diagnosis of hyperthyroid Graves disease scheduled to receive ablation therapy with radioiodine (Iodine-131): 17 patients were pretreated with antithyroid drugs, and 4 were not.

Methods: Antithyroid drugs were stopped 6 days before radioiodine therapy. Patients were monitored clinically and biochemically with measurement of free and total levels of thyroxine (T₄) and triiodothyronine (T₃) on days –6, –3, –1;the day of radioiodine therapy; and days 1, 2, 3, 4, 5, 7, and 14.

Results: Before radioiodine treatment and compared with baseline measurement, the mean increase in free T₄ levels after discontinuation of antithyroid therapy was 86% (95% CI, 16.1% to 156%), with a concurrent mean increase in free T₃ levels of 71.6% (CI, 31% to 112%). Radioiodine therapy resulted in a mean decrease in free T₃ levels of 28.7% (CI, –44.1% to –13.2%),a mean decrease in total T₃ levels of 22.9% (CI, –39.4% to –6.4%),and stability in free and total T₄ levels rather than aggravation of thyrotoxicosis. A smaller group of patients not receiving antithyroid drugs experienced a course qualitatively similar to that of pretreated patients after Iodine-131 treatment, with a mean reduction in free T₄ levels of 39.8% (CI, –69.9% to –9.7%)and a mean decrease in free T₃ levels of 49.4% (CI, –93.7% to –5.1%).

Conclusion: Short-term increases in thyroid hormone levels in patients with Graves disease receiving radioiodine ablation occur primarily as a result of discontinuing antithyroid therapy rather than as a result of treatment with Iodine-131. Stability or decrease in thyroid hormone levels, rather than further elevation, occurs during the 2-week interval after ablation therapy with Iodine-131. Antithyroid drug therapy before radioiodine ablation may have little effect on the short-term biochemical course after Iodine-131 therapy for Graves disease. The homogeneity of our sample regarding age, diagnosis, and general health may prevent application of these findings to other populations without further study.

Author and Article Information

From the Walter Reed Army Medical Center and Washington Hospital Center, Washington, D.C.
Request for Reprints: Henry B. Burch, MD, Endocrine-Metabolic Service, Walter Reed Army Medical Center, Washington, DC 20307-5001.
Disclaimer: The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of the Army or the Department of Defense.
Acknowledgments: The authors thank the nurses of the Kyle Metabolic Unit for assistance in collecting and organizing serum samples; Ms. Robin Howard and Dr. Audrey Chang for assistance with the statistical analysis; and Mr. Mack Burton for administrative support. This work was performed under the auspices of a research protocol approved by the Human Use Committee of the Department of Clinical Investigation, Walter Reed Army Medical Center.