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Discontinuing Antithyroid Drug Therapy before Ablation with Radioiodine in Graves Disease

Henry B. Burch, MD; Barbara L. Solomon, DNS; Leonard Wartofsky, MD; and Kenneth D. Burman, MD
[+] Article and Author 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.


Copyright ©2004 by the American College of Physicians


Ann Intern Med. 1994;121(8):553-559. doi:10.7326/0003-4819-121-8-199410150-00001
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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.

Figures

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Figure 1.
Changes in thyroid hormone levels after discontinuation of antithyroid therapy and administration of radioiodine in 17 patients.344334PPP1P0P0044

Values shown represent the mean; bars indicate the standard error of the mean. Discontinuing antithyroid therapy resulted in a rapid increase in all thyroid hormone levels measured, peaking on either day 1 (free triiodothyronine [T ] and total T3) or day 2 (free thyroxine [T ] and total T ) after Iodine-131 therapy. Thereafter, free T and total T levels rapidly decreased, followed by a gradual decrease in free T levels and maintenance of total T4 levels at a plateau value over the period of observation. * = significant at < 0.05 compared with baseline values; ** = < 0.001 compared with baseline values; † = < 0.05 compared with values from T ; ‡ = < 0.005 compared with values from T ; § = < 0.05 compared with values from T . T = the day of Iodine-131 treatment. To convert total T values to nmol/L and to convert free T values to pmol/L, multiply by 12.87. To convert total T3 values to nmol/L, multiply by 0.01536.

Grahic Jump Location
Grahic Jump Location
Figure 2.
Changes in thyroid hormone levels in four patients not receiving pretreatment with antithyroid drugs.4334P0P0P0P0P−10443

Values shown represent the mean; bars indicate the standard error of the mean. Compared with baseline values, administration of Iodine-131 resulted in a rapid decrease in free thyroxine (T ), free triiodothyronine (T ), and total T levels, with a more gradual decrease in total T levels. * = significant at < 0.05 compared with values from T ; ** = < 0.001 compared with values from T ; † = < 0.01 compared with values from T ; ‡ = < 0.005 compared with values from T ; § = < 0.05 compared with values from day T . T = the day of Iodine-131 treatment. To convert total T values to nmol/L and to convert free T values to pmol/L, multiply by 12.87. To convert total T values to nmol/L, multiply by 0.01536.

Grahic Jump Location

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