Hesse L M, Venkatakrishnan K, von Moltke L L, Shader R I, Greenblatt D J
Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, 136 Harrison Ave., Boston, Massachusetts, USA.
Drug Metab Dispos. 2001 Feb;29(2):133-40.
The kinetics of flunitrazepam (FNTZ) N-demethylation to desmethylflunitrazepam (DM FNTZ), and 3-hydroxylation to 3-hydroxyflunitrazepam (3-OH FNTZ), were studied in human liver microsomes and in microsomes containing heterologously expressed individual human CYPs. FNTZ was N-demethylated by cDNA-expressed CYP2A6 (K(m) = 1921 microM), CYP2B6 (K(m) = 101 microM), CYP2C9 (K(m) = 50 microM), CYP2C19 (K(m) = 60 microM), and CYP3A4 (K(m) = 155 microM), and 3-hydroxylated by cDNA-expressed CYP2A6 (K(m) = 298 microM) and CYP3A4 (K(m) = 286 microM). The 3-hydroxylation pathway was predominant in liver microsomes, accounting for more than 80% of intrinsic clearance compared with the N-demethylation pathway. After adjusting for estimated relative abundance, CYP3A accounted for the majority of intrinsic clearance via both pathways. This finding was supported by chemical inhibition studies in human liver microsomes. Formation of 3-OH FNTZ was reduced to 10% or less of control values by ketoconazole (IC(50) = 0.11 microM) and ritonavir (IC(50) = 0.041 microM). Formation of DM FNTZ was inhibited to 40% of control velocity by 2.5 microM ketoconazole and to 30% of control by 2.5 microM ritonavir. Neither 3-OH FNTZ nor DM FNTZ formation was inhibited to less than 85% of control activity by alpha-naphthoflavone (CYP1A2), sulfaphenazole (CYP2C9), omeprazole (CYP2C19), or quinidine (CYP2D6). Thus, CYP-dependent FNTZ biotransformation, like that of many benzodiazepine derivatives, is mediated mainly by CYP3A. Clinical interactions of FNTZ with CYP3A inhibitors can be anticipated.
在人肝微粒体以及含有异源表达的单个人类细胞色素P450（CYP）的微粒体中，研究了氟硝西泮（FNTZ）N-去甲基化生成去甲基氟硝西泮（DM FNTZ）以及3-羟基化生成3-羟基氟硝西泮（3-OH FNTZ）的动力学过程。FNTZ可被cDNA表达的CYP2A6（米氏常数[K(m)] = 1921微摩尔）、CYP2B6（K(m) = 101微摩尔）、CYP2C9（K(m) = 50微摩尔）、CYP2C19（K(m) = 60微摩尔）和CYP3A4（K(m) = 155微摩尔）进行N-去甲基化，也可被cDNA表达的CYP2A6（K(m) = 298微摩尔）和CYP3A4（K(m) = 286微摩尔）进行3-羟基化。在肝微粒体中，3-羟基化途径占主导，与N-去甲基化途径相比，其占内在清除率的80%以上。在根据估计的相对丰度进行校正后，CYP3A通过这两种途径均占内在清除率的大部分。这一发现得到了人肝微粒体化学抑制研究的支持。酮康唑（半数抑制浓度[IC(50)] = 0.11微摩尔）和利托那韦（IC(50) = 0.041微摩尔）可使3-OH FNTZ的生成减少至对照值的10%或更低。2.5微摩尔酮康唑可将DM FNTZ的生成抑制至对照速度的40%，2.5微摩尔利托那韦可将其抑制至对照值的30%。α-萘黄酮（CYP1A2）、磺胺苯吡唑（CYP2C9）、奥美拉唑（CYP2C19）或奎尼丁（CYP2D6）均未将3-OH FNTZ或DM FNTZ的生成抑制至对照活性的85%以下。因此，与许多苯二氮䓬衍生物一样，CYP依赖性FNTZ生物转化主要由CYP3A介导。可以预期FNTZ与CYP3A抑制剂之间会发生临床相互作用。
