Pharmacokinetics, Bioequivalence, and Safety of Levothyroxine Sodium Tablets in Healthy Chinese Subjects

Recently, a local pharmaceutical company produced levothyroxine sodium tablets, an endogenous drug that helps improve water‐salt metabolism and reduce myxedema. However, the bioequivalence of these tablets is not well known. The present study aimed to investigate the bioequivalence, pharmacokinetics, and safety of a single oral dose of 2 levothyroxine sodium tablets in healthy adult Chinese subjects under fasting conditions. The study used a single‐center randomized, single‐dose, 2‐sequence, 4‐period replicate crossover design. Forty‐eight subjects fasted for at least 10 hours before taking the medication. According to the literature, levothyroxine sodium is an endogenous narrow therapeutic index drug; therefore, baseline samples were collected before administration in healthy adult subjects. Blood specimens from all subjects were collected against the light within 48 hours to detect levothyroxine concentration in serum. A noncompartmental model was used for the analysis of pre‐ and post‐baseline correction pharmacokinetic parameters. The geometric mean ratio of the post‐baseline correction maximum plasma concentration and area under the concentration‐time curve from time 0 to 48 hours with a 90% confidence interval was calculated. The final data met the bioequivalence criteria. No serious adverse reactions were found, suggesting that the test and reference preparations of levothyroxine sodium tablets have a similar safety profile.