ICH M7（R1）第4类
杂质定义：Alerting structure, same alert in drug substance or compounds related to the drug substance (e.g., process intermediates) which have been tested and are non-mutagenic.
后面详细解释如下：An impurity with a structural alert that is shared (e.g., same structural alert in the same
position and chemical environment) with the drug substance or related compounds can be considered as non-mutagenic (Class 4 in Table 1) if the testing of such material in the bacterial mutagenicity assay was negative.
也就是说，如果一个杂质与API或者
中间体具有相同的警示结构（位点相同化学环境也相同），同时相应的API或者中间体经细菌致突变性实验证实为阴性的，可以被认为第四类杂质，当作非致突变杂质控制。这里就有一个问题，警示结构位置相同很好判断，相同的化学环境怎么认定？取代基不同比如API是某警示结构中带了某个取代基，杂质是另一种取代基，取代基不同肯定化学环境有差异吧，能认为化学环境还相同吗？有没有哪位老师肯不吝赐教解我疑惑？不胜感激！
