动物试验替代方法的适用边界

结论：可替代的终点在增加，但替代需要论证，不是自动成立

生物学评价中使用替代方法（体外方法、化学分析加风险评估）的空间在扩大，这既有伦理方面的推动，也因为部分体外方法的可靠性已经过验证。

但替代有边界。 有些终点已经有被广泛接受的体外方法；有些终点的体外方法还在发展中；有些终点目前仍难以用体外方法充分替代。

关键是：替代不是自动成立的，使用替代方法需要论证其对具体产品的适用性。 论证不充分，方法再先进也可能不被接受。

替代的可行程度

注意「可行程度」不等于「一定被接受」。 具体到某个产品、某个市场、某次提交，是否被接受还要看论证质量和当时的要求。

替代的两条路径

路径一：体外试验替代。 用体外方法代替相应的动物试验。适用于已有验证方法的终点。

路径二：化学分析加风险评估。 通过化学表征找出释放物质，评估其毒理学风险，从而回答某些全身性终点的问题。

第二条路径近年应用较多，特别是对全身毒性类的终点。它的前提是化学表征做得足够充分——覆盖面要广、检出限要低、未鉴定物质要有处理。

表征做得粗糙，这条路径就走不通。 所以选择这条路径实际上是把工作从动物试验转移到了分析化学和风险评估上，不是减少工作量。

替代的前提条件

使用替代方法需要满足：

方法本身经过验证。 方法的可靠性和相关性有依据。

方法适用于该产品类型。 有些体外方法对特定形态或特性的样品不适用，比如有色的、有细胞毒性的、难以浸提的材料。

样品处理方式合适。 浸提条件、样品制备要符合方法要求。

有适当的对照。 阳性对照、阴性对照、溶剂对照。

结果可解释。 出现可疑结果时有处理方案。

第二条最需要注意。 某些体外方法在遇到特定材料时会出现干扰，导致结果不可靠。选择方法前要确认样品特性与方法的适用范围匹配。

方法选择的考虑

产品特性优先。 材料形态、颜色、浸提难易度都影响方法适用性。

目标市场的接受度。 不同市场对替代方法的接受程度可能有差异，多市场产品要考虑较保守的一方。

数据的完整性。 替代方法的数据要能支撑结论，必要时几种方法组合使用。

时间与成本。 体外方法通常周期较短，但如果需要组合多个方法，总成本未必低。

风险等级匹配。 高风险产品使用替代方法时，论证要求更高。

提交时的论证

使用替代方法时，资料中应当说明：

为什么选择替代方法。 依据是什么。

方法的验证状态。 方法本身的可靠性依据。

方法对本产品的适用性。 这是论证的核心——不是泛泛说方法有效，而是说明对这个具体产品有效。

干扰因素的排除。 说明样品特性不会干扰方法。

结果的解释。 结果如何支撑该终点的结论。

局限性的说明。 替代方法覆盖不到的方面如何处理。

最后一条体现论证的严谨性。 承认方法的局限并说明如何补足，比声称方法完全等效更有说服力。

组合策略

实务中常用的是组合策略，而不是单一方法替代：

化学表征作为基础。 提供物质信息。

体外试验覆盖局部终点。 细胞毒性、刺激性等。

风险评估覆盖全身终点。 基于表征数据。

必要时保留少量动物试验。 对难以替代的终点。

这个组合的效果通常好于单一路径，因为各方法互补——化学数据说明有什么物质，体外试验反映材料的整体效应，风险评估把两者联系起来。

数据的可靠性说明

使用替代方法时，数据可靠性的说明尤其重要，因为审查方可能对方法不如对传统方法熟悉：

实验室的能力。 该方法是否在实验室的能力范围内、人员是否有相应经验。

方法的执行。 是否按方法要求执行、偏离之处如何说明。

对照的表现。 阳性对照是否给出预期结果，这是判断本次试验有效性的直接证据。

重复性。 平行样的一致性。

历史数据。 实验室该方法的历史对照数据范围。

第三项和第五项是说服力较强的证据。 阳性对照正常、结果落在历史范围内，说明本次试验是可信的。

不宜勉强替代的情形

有几种情况建议不要勉强用替代方法：

产品风险等级高且论证依据不足；目标市场对该方法接受度不明确；样品特性可能干扰方法而无法排除；时间紧张、没有余地处理可疑结果；以及缺少充分的化学表征数据支撑风险评估路径。

勉强替代的代价是：做完之后不被接受，还要重做，时间和成本都比一开始就按传统方法做更高。

判断的原则是看论证能不能站住，而不是看方法是否先进。

我们的做法

讨论方案时，我们会根据产品特性判断哪些终点适合用替代方法。如果材料特性可能干扰某个体外方法，我们会提前说明，避免做出来的数据不可用。

对于走化学分析加风险评估路径的产品，我们会把表征做得尽量充分——覆盖面、检出限、未鉴定峰的处理都会在方案中明确，因为这条路径的可行性完全取决于表征的质量。

如果你在考虑用替代方法，不确定对自己的产品是否适用，可以把材料信息和目标市场发过来一起讨论，或者直接联系：132 4819 8029。能力范围见服务介绍，送检要求见送检要求，其他问题见常见问题。

English version

Conclusion. The scope for alternative methods in biological evaluation, whether in vitro methods or chemical analysis combined with risk assessment, has been widening, driven both by ethical considerations and by validation of in vitro method reliability. There are boundaries, however. Some endpoints have widely accepted in vitro methods; for some the methods are still developing; and for some, adequate in vitro substitution remains difficult. The key point is that substitution is not automatic: using an alternative method requires justifying its applicability to the specific product. Without adequate justification, even a sophisticated method may not be accepted.

Feasibility by endpoint. Cytotoxicity is an in vitro method to begin with. Irritation has reasonably mature in vitro methods. Sensitisation has developing method combinations. Genotoxicity has some mature in vitro methods. Acute systemic toxicity can follow the chemical analysis and risk assessment route. Implantation response remains difficult to substitute adequately. Haemocompatibility can be partly performed in vitro. And chronic toxicity and carcinogenicity rely principally on the risk assessment route. Note that feasibility does not equal acceptance: whether a given product, market and submission accepts substitution still depends on the quality of the justification and the requirements at the time.

Two routes. The first is in vitro substitution, replacing the corresponding animal test with an in vitro method, applicable where validated methods exist. The second is chemical analysis with risk assessment, identifying released substances by characterisation and assessing their toxicological risk to answer certain systemic endpoints. The second has seen considerable use recently, particularly for systemic toxicity endpoints. It presupposes characterisation thorough enough in coverage and detection limits, with unidentified substances properly handled. Coarse characterisation closes this route. Choosing it therefore shifts work from animal testing to analytical chemistry and risk assessment rather than reducing it.

Preconditions. The method itself must be validated, with a basis for its reliability and relevance. The method must suit the product type, since some in vitro methods do not suit particular forms or characteristics such as coloured, cytotoxic or difficult-to-extract materials. Sample handling must suit the method in extraction conditions and preparation. Appropriate controls must be included, positive, negative and vehicle. And results must be interpretable, with a plan for handling equivocal outcomes. The second needs the most attention: certain materials interfere with certain in vitro methods and render results unreliable, so confirm before selecting a method that the sample's characteristics fall within its applicability.

Selection considerations. Product characteristics come first, since material form, colour and extractability all affect applicability. Target market acceptance varies, and multi-market products should follow the more conservative position. Data completeness matters, since the data must support the conclusion and several methods may need combining. Time and cost matter, since in vitro methods are usually quicker but combining several may not cost less overall. And risk level matters, since substitution for high-risk products demands stronger justification.

Justification at submission. Explain why the alternative was chosen and on what basis. State the method's validation status. Justify its applicability to this product, which is the core of the argument: not that the method is generally valid but that it is valid for this product. Exclude interference by explaining that the sample's characteristics do not disturb the method. Interpret the results, showing how they support the conclusion for that endpoint. And state the limitations, explaining how aspects the method does not cover are addressed. The last demonstrates rigour: acknowledging limitations and explaining how they are covered is more persuasive than claiming full equivalence.

Combination strategies. Practice usually favours a combination rather than substitution by a single method. Chemical characterisation forms the base, supplying substance information. In vitro testing covers local endpoints such as cytotoxicity and irritation. Risk assessment covers systemic endpoints on the basis of the characterisation. And a small amount of animal testing is retained where substitution is difficult. The combination generally works better than any single route, because the methods complement one another: chemical data show what substances are present, in vitro testing reflects the material's overall effect, and risk assessment connects the two.

How we handle it. When discussing protocols we judge from the product's characteristics which endpoints suit alternative methods, and where material characteristics might interfere with a particular in vitro method we say so in advance, to avoid generating unusable data. For products taking the chemical analysis route we make characterisation as thorough as we can, setting out coverage, detection limits and the handling of unidentified peaks in the protocol, because the viability of that route depends entirely on characterisation quality.

Send us the material information and target markets and we will discuss what suits your product. Phone or WeChat: +86 132 4819 8029.