Evaluating the utility of the Threshold of Toxicological Concern (TTC) and its exclusions in the biocompatibility assessment of extractable chemical substances from medical devices

The Threshold of Toxicological Concern (TTC) is a pragmatic approach used to establish safe thresholds below which there can be no appreciable risk to human health. Here, a large inventory of ~45,000 substances (referred to as the LRI dataset) was profiled through the Kroes TTC decision module within Toxtree v3.1 to assign substances into their respective TTC categories. Four thousand and two substances were found to be not applicable for the TTC approach. However, closer examination of these substances uncovered several implementation issues: substances represented in their salt forms were automatically assigned as not appropriate for TTC when many of these contained essential metals as counter ions which would render them TTC applicable. High Potency Carcinogens and dioxin-like substances were not fully captured based on the rules currently implemented in the software. Phosphorus containing substances were considered exclusions when many of them would be appropriate for TTC. Refinements were proposed to address the limitations in the current software implementation. A second component of the study explored a set of substances representative of those released from medical devices and compared them to the LRI dataset as well as other toxicity datasets to investigate their structural similarity. A third component of the study sought to extend the exclusion rules to address application to substances released from medical devices that lack toxicity data. The refined rules were then applied to this dataset and the TTC assignments were compared. This case study demonstrated the importance of evaluating the software implementation of an established TTC workflow, identified certain limitations and explored potential refinements when applying these concepts to medical devices.

Toxicological assessment compilation of selected examples of raw materials for homeopathic medicinal products

The considerable number of homeopathic medicinal products (HMP) on the German market and the staggering breadth of active substances of various origin along with the specific legal requirements of adequate safety principles posed the need to compile data on toxicologically evaluated raw materials. In line with the European regulatory framework, HMP applications must consider appropriate safety standards in analogy to conventional human medicinal products. This review presents an option for a systematic and scientifically substantiated approach for regulatory use. Furthermore, this paper provides a multitude of data for selected raw materials processed in HMP with up to now rather scarce knowledge and, thus, aims at filling data gaps on acceptable amounts per day (AAD). The inclusion of raw materials into the compilation was determined considering the frequencies of their occurrence in HMP in Germany along with the availability of appropriate safety assessments. This safety evaluation compilation represents a practical, fairly comprehensive and systematic set of more than 170 raw materials. It is designed to both effectively support regulatory decision making and to be recognized and exploited by applicants, stakeholders and the scientific community.

Utilizing Threshold of Toxicological Concern (TTC) with High Throughput Exposure Predictions (HTE) as a Risk-Based Prioritization Approach for thousands of chemicals

Regulatory agencies across the world are facing the challenge of performing risk-based prioritization of thousands of chemicals in commerce. Here, we present an approach using the Threshold of Toxicological Concern (TTC) combined with heuristic high-throughput exposure (HTE) modelling to rank order chemicals for further evaluation. Accordingly, for risk-based prioritization, chemicals with exposures > TTC would be ranked as higher priority for further evaluation whereas substances with exposures < TTC would be ranked as lower priority. An initial proof of concept, using a dataset of 7986 substances with previously modeled median and upper 95% credible interval (UCI) total daily median exposure rates showed fewer than 5% of substances had UCI exposures > the Cramer Class III TTC (1.5 μg/kg-day). We extended the analysis by profiling the same dataset through the TTC workflow published by Kroes et al (2004) which accounts for known exclusions to the TTC as well as structural alerts. UCI exposures were then compared to the appropriate class-specific TTC. None of the substances categorized as Cramer Class I or Cramer Class II exceeded their respective TTC values and no more than 2% of substances categorized as Cramer Class III or acetylcholinesterase inhibitors exceeded their respective TTC values. The modeled UCI exposures for the majority of the 1853 chemicals with genotoxicity structural alerts did exceed the TTC of 0.0025 μg/kg-day, but only 79 substances exceeded this TTC if median exposure values were used. For substances for which UCI exposures exceeded relevant TTC values, we highlight possible approaches for consideration to refine the HTE : TTC approach. Overall, coupling TTC with HTE offers promise as a pragmatic first step in ranking substances as part of a risk-based prioritization approach.

Antibiotics exposure and health risks: chloramphenicol

The antibiotic chloramphenicol (CAP) is banned from food production. Besides being a medicinal product, CAP is also a natural product, produced by Streptomyces Venezuelae. The lack of scientific data hampers setting of an Acceptable Daily Intake (ADI). Consequently, a maximum residue limit (MRL) in food could not be established. This was then translated into a zero tolerance using the so-called Minimum Required Performance Limit (MRPL) level, viz. the achievable detection limit in food, to guide the zero tolerance policy. The MRPL is clearly not relevant to food safety and human health but is solely related to analytical technological capabilities. The increase in the latter enables detection at ever-lower levels and ignores toxicological relevance. We here provide arguments to use a Threshold of Toxicological Concern (TTC) for CAP that can accommodate developing toxicological insights.

Complex mixtures: relevance of combined exposure to substances at low dose levels

Upon analysis of chemically complex food matrices a forest of peaks is likely to be found. Identification of these peaks and concurrent determination of the toxicological relevance upon exposure is very time consuming, expensive and often requires animal studies. Recently, a safety assessment framework based on the Threshold of Toxicological Concern (TTC) was published to assess the safety of chemically complex matrices more efficiently. In this safety assessment framework, the toxicological relevance of exposure to unidentified substances in chemically complex food matrices can be related to the Cramer class III TTC threshold, currently set at 90 μg/day. However, possible additive or synergistic effects of combined exposure is not covered. The current evaluation describes the relevance of combined low dose exposure to unidentified substances in chemically complex food matrices. It is concluded that to some extent cumulative effects at exposure levels for each substance at or below the Cramer class III TTC threshold, being present in a complex mixture including food, might occur. However the health relevance of possible cumulative effects at this dose level is considered to be that low that a need for a correction factor to cover possible cumulative effects is very low to absent.