Administration of Levothyroxine 45 - 60 Minutes before Breakfast Improves Biochemical Availability as Evidenced by Reduced Thyrotropin Levels

Introduction: Serum Thyrotropin (TSH) level is used to assess adequacy of levothyroxine dosing for patients with hypothyroidism. Some patients have raised TSH levels despite being on an adequate dose of levothyroxine (100 mcg/day 200 mcg/day). Aim: To evaluated the effect of advising patients to take their levothyroxine 45 60 minutes before breakfast on raised serum TSH levels. Patients and Methods: Rather than increase the dose, patients with raised TSH levels were asked to take their levothyroxine at least 45 60 minutes before breakfast and other oral medications. Thyroid Function Tests were assessed at base line and repeated after two months. Results: Data from ten patients who presented between 2008 and 2010 were analyzed (9 females, 1 male): with median (IQR) age: 39 (33 49) years and duration of hypothyroidism: 6 (3 7.8) years. Median (IQR) levothyroxine dose was 175 (144 250) mcg, serum free-Thyroxine (free-T4): 13 (10.5 17.1) pmol/L and serum TSH: 12.63 (6.2 48.3) mIU/L. After two months all patients demonstrated biochemical improvement; a decrease in serum TSH to 3.15 (0.4 6.1) mIU/L accompanied by an increase in serum free-T4 to 17.7 (14.8 21.3) pmol/L. Both changes were statistically significant (p < 0.05 and p < 0.01, respectively). The median (IQR) percentage TSH reduction was 83.5 (40.3 95.8) mIU/L and this bore no significant correlation with the initial TSH level (rs = 0.2, p = 0.58). Conclusion: Changing levothyroxine administration to 45 60 minutes before breakfast and other oral medications reduced TSH levels by 40% 96% in all patients. We recommend this advice for all patients with hypothyroidism on adequate doses of levothyroxine but still appear biochemically under-replaced.