Abstract

Background: Patients with hypothyroidism are generally recommended to take their levothyroxine(LT4) half an hour or one hour before breakfast because LT4 absorption increases with fasting. However, data related to whether bedtime or morning intake of levothyroxine has a better influence thyroid-stimulating hormone (TSH) equilibrium limited. This aim of this study was to compare the effect of switching the intake time of LT4 from morning to bedtime clinical, hormonal, and biochemical parameters.

Material and Method: A total of 60 patients (55 females, 5 males) with a mean age of 45.5±13.3 years (range, 21-74years) were enrolled in the study. The route of LT4 administration in patients with routine dosing schedules for LT4 treatment of 60minutes before breakfast was switched to bedtime (at least three hours after the evening meal), and patients were followed up for 12 weeks.

Results: A slight but insignificant increase in TSH levels (2.8±1.3 to 3.6±3.8IU/L, p>0.05) was observed. The serum-free T4 levels in patients taking LT4 at bedtime were significantly higher than in patients taking LT4 at breakfast (1.2±0.1 vs.1.1±0.1ng/dL, p<0.05). Body weight (73.5±15.7 to 74.5±16.2kg, p<0.05) and body mass index (28.8±5.7 to 29.1±6.0kg/m2, p<0.05) were significantly increased during follow-up. Ten(16.7%) patients reported newly developed night sweats and 8 (13.3%) had increased appetite at the end of the study.

Conclusions: Physicians may recommend bedtime LT4 regimens to patients with hypothyroidism who have poor adherence to regular morning medical treatment. However, the possibility of an increase in some symptoms should be kept in mind.

Keywords: Levothyroxine; Hypothyroidism; Timing of intake