The cliff-edge of toxicological concern: highlighting the potential issues of an over-reliance on "less-than-lifetime" thresholds.

IF 2.2 4区 医学 Q3 TOXICOLOGY Toxicology Research Pub Date : 2024-10-27 eCollection Date: 2024-10-01 DOI:10.1093/toxres/tfae178
Christopher J Waine, Peter Watts, James Hopkins
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Abstract

The Threshold of Toxicological Concern (TTC) is a very well-established concept in applied toxicology, and has become a key tool for the pragmatic human health risk assessment of data-poor chemicals. Within the pharmaceutical sector, regulatory guidance on genotoxins defaults to a TTC of 1.5 μg/day equating to a maximum lifetime cancer risk of 1 in 100,000. Higher doses for drug products where exposures are intermittent or otherwise "less-than-lifetime" (LTL) are also considered tolerable. This also allows substance-specific lifetime Acceptable Intakes (AIs) for known genotoxic carcinogens to be scaled up for shorter durations. The default TTCs for assessing LTL exposures build in conservatism such that there is deviation from strict linearity. However, close to the boundaries between LTL categories there can be such a difference in the default tolerable intakes that a health risk assessment can yield conflicting results. We have presented a theoretical case study based on our recent work that illustrates this apparent "cliff-edge." The total acceptable cumulative dose over a 56-day treatment is - in absolute terms - one third of that allowed over 28 days, despite the maximum cancer risk of the longer exposure being an order of magnitude higher. Our analysis suggests the need for careful consideration of what might represent tolerable exposures in the region of the category limits, rather than simply adopting the hardline default. Where a potential patient exposure is found to be above a default value, there is real value in refining the cancer risk estimates using the Lifetime Cumulative Dose approach.

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毒理学关注的悬崖边缘:强调过度依赖 "少于终身 "阈值的潜在问题。
毒理学关注阈值(TTC)是应用毒理学中一个非常成熟的概念,已成为对缺乏数据的化学品进行务实的人类健康风险评估的重要工具。在制药领域,有关基因毒素的监管指南默认 TTC 为 1.5 微克/天,相当于一生中最大癌症风险为十万分之一。对于间歇性接触或 "低于终生"(LTL)接触的药物产品,更高的剂量也被认为是可容忍的。这也使得针对特定物质的已知基因毒性致癌物质的终生可接受摄入量(AIs)可以在较短时间内按比例放大。评估 LTL 暴露的默认 TTC 具有保守性,因此会偏离严格的线性。然而,在接近低限寿命类别之间的界限时,默认的可容忍摄入量可能会有很大差异,以至于健康风险评估会产生相互矛盾的结果。我们在近期工作的基础上提出了一个理论案例研究,以说明这种明显的 "悬崖边缘"。在 56 天的治疗中,可接受的累积总剂量的绝对值是 28 天允许剂量的三分之一,尽管更长时间暴露的最大癌症风险要高出一个数量级。我们的分析表明,有必要仔细考虑类别限值范围内的可容忍暴露量,而不是简单地采用强硬的默认值。当发现患者的潜在暴露量高于默认值时,使用终生累积剂量法对癌症风险估算进行改进是有实际价值的。
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来源期刊
Toxicology Research
Toxicology Research TOXICOLOGY-
CiteScore
3.60
自引率
0.00%
发文量
82
期刊介绍: A multi-disciplinary journal covering the best research in both fundamental and applied aspects of toxicology
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