The increased uptake and use of smaller blood volumes for sampling (microsampling) has the potential to refine and reduce animal use, particularly for toxicokinetics. We have identified the barriers to adoption through workshops and surveys of company practice. A working group has been active since 2012 to share data and experience, make evidence-based recommendations on best practice and inform changes in regulatory guidelines. We have developed a practical resource to disseminate study designs which reduce animal use and protocols which refine procedures.
To maximise the 3Rs impact, increased uptake in GLP regulatory toxicology studies is needed. Since acceptance of microsampling was supported by updates to regulatory guidance in 2017 (ICH S3a Q&A), many more companies now regularly adopt this technique within GLP studies. In 2021 we initiated another survey to establish the current practice and to identify remaining barriers to wider adoption.
Toxicokinetic analysis identifies the level of drug exposure which elicits an adverse event in animals. Most short and long-term toxicity studies include ‘main study animals’ which are used to determine potential adverse effects, plus ‘satellite animals’ for toxicokinetics. Direct biological comparison of exposure and adverse events in the same animal is limited by the volume of blood required for analysis – typically around 200µl per time point.
For many small molecules, biologics and biomarkers, bioanalytical methods exist that allow drugs to be measured in blood samples of less than 50µl per time point. This provides the opportunity to take microsamples of blood from the main study group without the need for satellite animals, giving scientific as well as 3Rs benefits. Removing the need for specific groups of rodents for the sole purpose of toxicokinetics represents the single biggest opportunity to reduce the use of animals in regulatory toxicology studies – providing up to a 55% reduction for some studies.
Sparrow S et al. (2011). Opportunities to minimise animal use in pharmaceutical regulatory general toxicology: A cross company review. Regulatory Toxicology and Pharmacology 61(2): 222-229. doi:10.1016/j.yrtph.2011.08.001
Chapman K et al. (2014). Overcoming the barriers to the uptake of nonclinical microsampling in regulatory safety studies. Drug Discovery Today 19(5): 528-32. doi:10.1016/j.drudis.2014.01.002