| Starting Therapy With High-Dose Levothyroxine Is Safe in Asymptomatic Cardiac Patients Laurie Barclay, MD June 23, 2003 — Starting therapy with high-dose levothyroxine (L-T4) is safe in asymptomatic cardiac patients, according to the results of a prospective, double- blind, randomized trial presented on June 21 at the 85th annual meeting of The Endocrine Society (Endo 2003) held in Philadelphia, Pennsylvania. Previous studies addressing the safety of high-dose L-T4 in cardiac disease have usually started with a low dose and have gradually increased the dose. These studies have been "anecdotal, retrospective, biased," according to senior author Arie Berghout, FRCP, an endocrinologist and head of the Department of Medicine at Medical Center Rotterdam in South Netherlands. "This is the first randomized, double-blinded trial," he told Medscape. "The implication is that you don't have to treat your patients with primary hypothyroidism with a low starting dose of l-thyroxine but can give the full replacement dose from the start, given that there is no history of angina pectoris." In this study, 51 consecutive hypothyroid patients with normal dobutamine stress echocardiography were randomized to L-T4 treatment at a dose of either 1.6 µg/kg body weight or 25 µg daily, in stratified blocks according to thyroid-stimulating hormone (TSH) level. Mean starting dose was 128 vs. 25 µg L-T4, given in liquid form at bedtime. The dose of L-T4 was adjusted every four weeks. Biochemical measurements, bicycle ergometry (XECG) and symptoms scores were obtained at baseline and at four- to 12-week intervals until 48 weeks. At baseline, both groups were similar in age, sex distribution, TSH, FT4, TT3, total cholesterol, body mass index, heart rate, blood pressure, and symptoms score. At four weeks, mean values for the 1.6 µg/kg group vs. the 25 µg group, respectively, were TSH, 15.5 vs. 53.1 mU/L (P = .01); FT4, 18.7 vs. 10.4 pmol/L (P < .001); TT3, 2.3 vs. 1.8 nmol/L (P = .01); heart rate, 70 vs. 64 bpm (P <.05). Cholesterol levels and symptoms score were similar in both groups, and blood pressure and body mass index did not change. None of the patients had angina pectoris or serious arrhythmias during treatment. One patient receiving 1.6 µg/kg had a nonsignificant ST depression on XECG at 12 and 24 weeks. At 12 weeks, exercise performance improved by 14% in the 1.6 µg/kg group vs. 0% in the 25 µg group, but at 24 weeks and thereafter, both groups were comparable in all respects, including exercise performance and quality of life. "No patient in our study [had] any signs of silent cardiac ischemia either by bicycle ergometry or by dobutamine stress test, in contrast for instance to patients with type 2 diabetes mellitus," Dr. Berghout said. "This raises the question whether primary hypothyroidism is indeed a risk factor for coronary ischemia. It could be that a far more important effect of hypothyroidism on the heart is diastolic dysfunction, which has been demonstrated in several studies. In that case, more rapid restoration of cardiac function could be more important." There was no external funding for this study, and the authors report no pertinent financial disclosures. Endo 2003: Abstract P3-674. Presented June 21, 2003. Reviewed by Gary D. Vogin, MD |
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