Hypotension is the dose-limiting side effect of the radio-protective drug Amifostine and results from relaxation of the vascular smooth muscle, which is directly mediated by the active metabolite, WR-1065, of Amifostine. The route of administration (currently FDA-approved only for intravenous administration) and the rapid metabolic conversion of Amifostine combine to yield high systemic levels of WR-1065 and facilitate the onset of hypotension. Research efforts aiming to optimize the delivery of WR-1065 to maintain efficacy while reducing its peak, systemic concentration below levels that induce hypotension are underway. To fully characterize the effect of reduced dose levels and alternative routes of administration of Amifostine on systemic WR-1065 concentrations, improved analytical techniques are needed. We have developed and evaluated a highly sensitive method for measuring WR-1065 in rat plasma that employs chemical derivatization, protein precipitation and UPLC-MS/MS analysis. The method exhibits a limit of quantification (LOQ) of 7.4 nM in plasma, which is a significant improvement over conventional approaches that utilize LC-electrochemical detection (ECD) (LOQ 150 nM or higher). The method was assessed in a pharmacokinetics study in rats administered Amifostine intravenously and via direct jejunal injection (10 mg/kg each route). The bioavailability of WR-1065 was 61.5% after direct jejunal injection indicating rapid conversion and absorption of the metabolite in the intestinal tract. This demonstrates that an oral formulation of Amifostine designed for site-specific release of the drug in the upper GI tract can deliver systemic absorption/conversion to WR-1065, provided that the formulation protects the therapeutic from gastric decomposition in the stomach.

低血压是放射防护药物氨磷汀的剂量限制性副作用，是由血管平滑肌松弛引起的，而血管平滑肌松弛是由氨磷汀的活性代谢物 WR-1065 直接介导的。给药途径（目前 FDA 批准仅用于静脉给药）和氨磷汀的快速代谢转化相结合，产生高全身水平的 WR-1065 并促进低血压的发生。旨在优化 WR-1065 的输送以保持疗效，同时将其峰值全身浓度降低到导致低血压的水平的研究工作正在进行中。为了充分表征降低剂量水平和替代给药途径 Amifostine 对全身 WR-1065 浓度的影响，需要改进分析技术。我们开发并评估了一种高灵敏度的方法，用于测量大鼠血浆中的 WR-1065，该方法采用化学衍生化、蛋白质沉淀和 UPLC-MS/MS 分析。该方法在血浆中的定量限 (LOQ) 为 7.4 nM，与使用 LC 电化学检测 (ECD)（LOQ 150 nM 或更高）的传统方法相比有了显着改进。该方法在大鼠静脉注射氨磷汀和直接空肠注射（每种途径 10 mg/kg）的药代动力学研究中进行了评估。直接空肠注射后，WR-1065 的生物利用度为 61.5%，表明代谢物在肠道中快速转化和吸收。