1 Division of Endocrinology and Metabolism, Department of Medicine, Schulich School of Medicine and Dentistry, Western University , London, Canada .
Thyroid. 2013 Nov;23(11):1374-8. doi: 10.1089/thy.2013.0014. Epub 2013 Oct 16.
Levothyroxine (L-T4) absorption varies between individuals, and can be affected by various concomitantly administered drugs. Case reports have indicated an association between cotreatment with ciprofloxacin or rifampin and hypothyroidism in patients on a stable L-T4 dose.
The effects of two antibiotics on T4 absorption were prospectively assessed in a double-blind, randomized, crossover fashion. Eight healthy volunteers received 1000 μg L-T4 combined with placebo, ciprofloxacin 750 mg, or rifampin 600 mg as single doses. We measured total plasma thyroxine (T4) concentrations over a 6-hour period after dosing using liquid chromatography-tandem mass spectrometry. For each study arm, areas under the T4 plasma concentration-time curve (T4 AUCs) were compared.
Coadministration of ciprofloxacin significantly decreased the T4 AUC by 39% (p = 0.035), while, surprisingly, rifampin significantly increased T4 AUC by 25% (p = 0.003).
Intestinal absorption of L-T4 is differentially affected by acute coadministration of ciprofloxacin or rifampin. Mechanistic studies focused on intestinal and possibly hepatic thyroid hormone transporters are required to explain the observed drug interactions with L-T4.
左甲状腺素（L-T4）的吸收因人而异，并且可能受到同时给予的各种药物的影响。病例报告表明，在稳定剂量的 L-T4 治疗的患者中，与环丙沙星或利福平联合治疗与甲状腺功能减退之间存在关联。
以双盲、随机、交叉方式前瞻性评估两种抗生素对 T4 吸收的影响。8 名健康志愿者单次给予 1000μg L-T4 联合安慰剂、环丙沙星 750mg 或利福平 600mg。给药后 6 小时内使用液相色谱-串联质谱法测量总血浆甲状腺素（T4）浓度。对于每个研究臂，比较 T4 血浆浓度-时间曲线下面积（T4 AUCs）。
环丙沙星的联合给药显著降低 T4 AUC 达 39%（p=0.035），而令人惊讶的是，利福平显著增加 T4 AUC 达 25%（p=0.003）。
L-T4 的肠内吸收受到环丙沙星或利福平的急性联合给药的不同影响。需要进行针对肠道和可能的肝甲状腺激素转运蛋白的机制研究，以解释与 L-T4 观察到的药物相互作用。
