Designs of preclinical safety (PCS) studies

For study designs see the corresponding OECD and other guidelines, textbooks, as well as other publications by individual and group experts. The discussion below is limited to in vivo studies for detection of general toxicity, safety pharmacology-related toxicity and carcinogenicity. For studies for detection of in vivo reproductive toxicity and in vitro studies please refer to guidelines, textbooks and other publications.

Attached is a proposal for Study designs.

The design of in vivo general toxicity studies includes parameters such as listed below, e.g.

  • In-life
    • General observation, possibly supplemented by closer and more frequent investigations of behavior (especially CNS-related parameters) and respiration
    • Parameters for hematology, clinical chemistry and urine analysis
    • Electrocardiographic (ECG) investigations mainly in non-rodents, possibly supplemented by extended jacketed ECG for safety pharmacology investigations
    • Toxicokinetic investigations at several timepoints generally during 24 hours, including timepoints for the maximal concentration; at least after single application and after the last application

    For selected cases investigation of genomic parameters, local reactions upon parenteral application, etc. are indicated. Also investigations of hormones have to be mentioned; the latter may show great variations and circadian rhythms

    The value of biomarkers is highlighted in the presentation Biomarkers in toxicology and disease progression. It is shown that biomarkers are indispensable and that much progress is made in this area, though the development of new markers is costly. It is often insufficient to use one biomarker or one type of biomarkers alone for a given condition, as the pattern of biomarker changes is generally more meaningful. Biomarkers often allow earlier detection of adverse effects, thus speed up and increase the safety of drug development, increase our knowledge, support differentiation of exposed and/or treated populations, etc.

  • Post-mortem investigations with necropsy including gross observations, organ weights and preservation of organs with abnormal weights or inspection findings and preservation of normal organs as required, generally in formalin

    These investigations are generally followed by histopathological investigations of the preserved organs, cut at few µm after embedment in paraffin and generally stained by hematoxylin and eosin (H&E), using standardized nomenclature and well-defined grading criteria (see e.g. RITA database). For special cases, additional investigations are performed such as special staining, staining for immunohistochemistry (IHC), morphometric investigations to ascertain relatively subtle morphologic changes¹, microdissection techniques, etc. Example for a special case: potential immunological effects can be suspected, if organ weights and histological results of lymphoreticular organs are abnormal

Attached are proposals for

The selection of animals should provide models reflecting the (anticipated) situation in man, though – without conflicting evidence – testing e.g. of normal small molecules is generally done in rodents (rats, plus mice for carcinogenicity testing) and non-rodents (dogs, occasionally minipigs; rabbits for reproductive studies). As explained in Animals used in PCS, biologics, including vaccine candidates, should be tested in responsive species.

The duration of in vivo studies needs to fulfill the requirements especially of ICH M3(R2). See also Type, duration and dose of regulatory studies.

ICH M3(R2) also defines the high dose for in vivo studies (see e.g. Preclinical safety program – Regular - ICH M3(R2)). If genotoxicity endpoints are to be incorporated into a general in vivo toxicity study, then an appropriate maximum dose should be selected based on an MFD, MTD or limit dose of 1000 mg/kg/day.

Special considerations apply to the testing for carcinogenicity (presentation Carcinogenicity studies - Duration and dose selection). In particular, the dose selection is critical to avoid tumorigenicity not related to relevant carcinogenic effects.

Absorption-distribution-metabolism-excretion (ADME)-related investigations are summarized in ADME-related studies. See also guidelines (e.g. ICH M3(R2) and ICH S3A and B) and the Summaries of regulatory development related to PCS.

See also the suggestion for a form called Some relevant PCS findings.

 

¹ A doubling of the volume means that the linear dimensions change by the third root, that is by 1.26, which is close to impossible to see