Zheng J J, Chan K K, Muggia F
School of Pharmacy, University of Southern California, Los Angeles 90033.
Cancer Chemother Pharmacol. 1994;33(5):391-8. doi: 10.1007/BF00686268.
Stability and preclinical pharmacokinetics of isophosphoramide mustard (IPM), an active metabolite of ifosphamide, were investigated using analytical methods developed in this laboratory. For stability evaluation of IPM we used a rapid, high-pressure liquid chromatographic (HPLC) method by which IPM is analyzed directly from aqueous solutions without derivatization on a 10-microns C-18 reversed-phase column with theophylline as the internal standard. IPM in sodium phosphate buffers was found to undergo pH-dependent first-order degradations. At pH 7.4 and 38 degrees C, the IPM solution showed a half-life of 45 min. A gas chromatographic-mass spectrometry (GC/MS) method for the analysis of IPM in plasma was also developed. This method utilized solid-phase extraction with deuterium-labeled IPM as the internal standard. The routine detection limit for the assay was 50 ng/ml with within-run and between-run coefficients of variation of 6% and 11%, respectively. By this method, stability of IPM in plasma and in RPMI 1640 tissue culture medium was evaluated, and its pharmacokinetics in the Sprague-Dawley rat following i.v. administration at 40 mg/kg were investigated. IPM was found to be more stable in these media, with half-lives in the range of 100 min. IPM plasma pharmacokinetics were found to decline monoexponentially with terminal half-lives ranging from 6.8 to 18.7 min and total clearance between 6.0 and 18.3 ml/min. Plasma protein binding of IPM was found to be 55%, and the partition ratio between plasma and red blood cells of 4.9 to 1, respectively. Cytotoxicity of IPM to L1210 cells was evaluated, and the results indicated that the IC50 with 1-h and 4-h exposure was 33 and 15 microM, respectively. Based on these data, IPM plasma levels in the rat declined below the IC50 in about 1 h at this dose. More frequent dosing or infusion may be necessary to maintain adequate drug levels for antitumor activity when IPM is administered directly.
采用本实验室开发的分析方法，对异环磷酰胺的活性代谢产物异环磷酰胺氮芥（IPM）的稳定性和临床前药代动力学进行了研究。为评估IPM的稳定性，我们使用了一种快速高压液相色谱（HPLC）方法，通过该方法可在10微米C-18反相柱上以茶碱为内标，直接从水溶液中分析IPM，无需衍生化。发现IPM在磷酸钠缓冲液中会发生pH依赖性的一级降解。在pH 7.4和38℃条件下，IPM溶液的半衰期为45分钟。还开发了一种用于分析血浆中IPM的气相色谱-质谱联用（GC/MS）方法。该方法采用以氘标记的IPM为内标的固相萃取。该测定方法的常规检测限为50 ng/ml，批内和批间变异系数分别为6%和11%。通过该方法，评估了IPM在血浆和RPMI 1640组织培养基中的稳定性，并研究了其在40 mg/kg静脉注射后在Sprague-Dawley大鼠体内的药代动力学。发现IPM在这些介质中更稳定，半衰期在100分钟左右。发现IPM的血浆药代动力学呈单指数下降，终末半衰期在6.8至18.7分钟之间，总清除率在6.0至18.3 ml/min之间。发现IPM的血浆蛋白结合率为55%，血浆与红细胞之间的分配比为4.9比1。评估了IPM对L1210细胞的细胞毒性，结果表明1小时和4小时暴露的IC50分别为33和15 microM。基于这些数据，在此剂量下，大鼠体内的IPM血浆水平在约1小时内降至IC50以下。当直接给予IPM时，可能需要更频繁给药或输注以维持足够的药物水平以发挥抗肿瘤活性。
