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.