REPLY
Levothyroxine Therapy
Susan J. Mandel, MD;
Gregory A. Brent, MD; and
P. Reed Larsen, MD
1 April 1994 | Volume 120 Issue 7 | Pages 619-620
IN RESPONSE:
We agree that the benefits of levothyroxine therapy for all patients with solitary thyroid nodules have not been clearly established. In one randomized controlled study, the nodule volume decreased significantly from baseline in those patients receiving levothyroxine but not placebo [1]. Similar results were not achieved in other studies discussed. However, as Dr. Leinung points out, TSH-suppressive therapy may forestall or prevent surgery with its morbidity and cost in selected patients. Because such levothyroxine-responsive nodules cannot be identified by pretreatment variables [2], we have attempted to devise a rational approach to therapy. To minimize the potential morbidity associated with therapy, we advocate individualizing dosage requirements by using sensitive serum TSH assays, limiting the therapeutic trial period, and withdrawing levothyroxine to establish a causal relation. Levothyroxine therapy for thyroid nodules has also been suggested by others [3].
As noted by Dr. Liel, because activated charcoal does reduce levothyroxine absorption, its use has been recommended in the treatment of thyroid hormone overdosage [4]. We agree that the lovastatin-levothyroxine interaction is still tenuous. For this reason, lovastatin was listed in our Table 2 as a drug that "possibly" blocks levothyroxine absorption. We also wish to call to readers' attention a recent report that sodium polystyrene sulphonate (Kayexalate; Sanofi Winthrop Pharmaceuticals, New York, New York) also interferes with intestinal absorption of levothyroxine [5] and may increase levothyroxine requirements.
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Author and Article Information
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Harvard Medical School; Brigham and Women's Hospital; 75 Francis Street; Boston, MA 02115
1. Gharib H, James EM, Charboneau JW, Naessens JM, Offord KP, Gorman CA. Suppressive therapy with levothyroxine for solitary thyroid nodules. N Engl J Med. 1987; 317:70-5.
2. Cheung PS, Lee JM, Boey JH. Thyroxine suppressive therapy of benign solitary thyroid nodules: a prospective randomized study. World J Surg. 1989; 13:818-22.
3. Mazzaferri EL. Management of a solitary thyroid nodule. N Engl J Med. 1993; 328:553-9.
4. Lewander W. Thyroid hormone overdose. Clinical Toxicology Review. 1984; v.6.
5. McLean M, Kirkwood I, Epstein M, Jones B, Hall C. Cation-exchange resin and inhibition of intestinal absorption of thyroxine. Lancet. 1993; 341:1286.
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