Best practices for developmental toxicity assessment for classification and labeling.

Many chemicals are going through a hazard-based classification and labeling process in Europe. Because of the significant public health implications, the best science must be applied in assessing developmental toxicity data. The European Teratology Society and Health and Environmental Sciences Institute co-organized a workshop to consider best practices, including data quality and consistency, interpretation of developmental effects in the presence of maternal toxicity, human relevance of animal data, and limits of chemical classes. Recommendations included larger historical control databases, more pharmacokinetic studies in pregnant animals for dose setting and study interpretation, generation of mechanistic data to resolve questions about whether maternal toxicity is causative of developmental toxicity, and more rigorous specifications for what constitutes a chemical class. It is our hope that these recommendations will form the basis for subsequent consensus workshops and other scientific activities designed to improve the scientific robustness of data interpretation for classification and labeling.

Teratology testing under REACH.

REACH guidelines may require teratology testing for new and existing chemicals. This chapter discusses procedures to assess the need for teratology testing and the conduct and interpretation of teratology tests where required.

Combined fertility and embryotoxicity study.

Under normal circumstances, fertility and embryotoxicity studies are run separately according to the ICH S5(R2) guideline for the detection of toxicity to reproduction of medicinal products (1). However, the flexible approach of the S5(R2) guideline also allows the reproduction stages covered in the fertility and embryo-fetal development studies (stages A to D) to be combined into a single study design. The administration period covers the pre-mating and gestation phases through to closure of the hard palate. The principal advantages of the combined study include reductions in the number of animals required and cost. Although the rat is the routine species of choice, the mouse may also be used.

Teratology studies in the rabbit.

The rabbit is generally the non-rodent species or second species after the rat recommended by the regulatory authorities and is part of the package of regulatory reproductive studies for the detection of potential embryotoxic and/or teratogenic effects of pharmaceuticals, chemicals, food additives, and other compounds, including vaccines (see Chapters 1-7).Its availability, practicality in housing and in mating as well as its large size makes the rabbit the preferred choice as a non-rodent species. The study protocols are essentially similar to those established for the rat (Chapter 9), with some particularities. The study designs are well defined in guidelines and are relatively standardized between testing laboratories across the world.As for the rat, large litter sizes and extensive background data in the rabbit are valuable criteria for an optimal assessment of in utero development of the embryo or fetus and for the detection of potential external or internal fetal malformations.

Historical control data in reproductive and developmental toxicity studies.

Reproductive and developmental toxicity studies in laboratory animals are conducted as part of the process of evaluating the risk of pharmaceuticals and chemicals to human reproduction and development. In these studies, comparison of data from groups dosed with the test article to a concurrent control group is considered the most relevant approach for the interpretation of adverse effects. However, differences between the concurrent control and treated groups may arise by chance alone, and in some instances may even appear to be dose-related. These limitations of the concurrent control group are of particular concern when interpreting fetal malformation data because malformations are rare events that can be better characterized when incidences in both concurrent control and treated groups are compared to a larger set of control values. Historical control data can be useful not only to understand the range of normal for a given endpoint but also to monitor the biological variability over time due to various external factors (e.g., genetic changes in a strain, changes at the breeding facility). It can also serve to track the performance of the laboratory and identify any changes in the data that may be the result of internal factors at the performing laboratory due to modification in animal diet, seasonal changes, or even the proficiency of the technicians in handling animals and recording fetal and offspring observations. This chapter will provide the reader with guidance on building a laboratory historical control database and applying it to the scientific interpretation of reproductive and developmental toxicity data. Information on sources of external historical control data will be provided and some perspective given on the utility of this data. A discussion of the presentation of historical control data with descriptive statistics will be accompanied by examples of tabulation of the data. Supernumerary rib will be used as an example of how historical control data can be used for data interpretation.

Suggested statistical standards for NTT manuscripts: notes from two of your reviewers.

The purpose of a scientific paper in this journal is to persuade the reader of some important or potentially important facts. For a reader to be persuaded, first the manuscript reviewers must be persuaded, and if the manuscript involves statistical reasoning, at least one of those reviewers is likely to be a statistician. This invited article, by two long-time reviewers for Neurotoxicology and Teratology (NTT) who are also contributors of statistical papers, surveys some of the principles that render a manuscript more persuasive or less persuasive in our eyes. These principles are overwhelmingly not statistical but logical. For one typical NTT manuscript theme, the relation between some toxic exposure and one or more negative outcomes in humans, the aspects of manuscripts we scrutinize most closely include biological plausibility, dose-response relationships, breadth of evidence, adjustments for measurement bias, attention to assumptions and scatterplots in the search for confounds, and, in general, a sincere attempt to enunciate and then refute plausible hypotheses rival to the one the investigators prefer. The literature of excellent studies in other fields provides ample instances of good practice in these matters; we review it in those fields for applications in ours. Formal statistical significance testing plays almost no role in the most persuasive papers. In particular, findings that appear only after "adjustment for covariates" are never considered credible by these reviewers; we explain our reasons at length, and suggest alternatives.