Refinement by gentle handling of mice affects oral-dosing pharmacokinetic end points and response to stress under drug administration and sampling

Lifting mice by their tails is a common handling method used for laboratory mice, yet it causes substantial stress. Alternative handling methods have a positive impact on animal welfare, but, there are limited studies on the effects of handling and habituation on scientific endpoints; hindering implementation and refinement in academia and industry. The purpose of this study was to investigate the effects of handling method (tail lifting vs. tube lifting) and habituation to handling (habituation) on drug uptake, exposure, and welfare parameters in a basic pharmacokinetic study. CD1 mice were either tail lifted without habituation, tube lifted without habituation, or tube lifted and habituated using a 10-day habituation protocol. A compound (mexiletine) was then administered by oral gavage and a 24 h pharmacokinetics study was performed in an industrial setting. The habituated group had a higher maximum serum concentration (C_max), lower time to C_max (T_max) and a 30 % higher drug exposure than the tail and tube-lifted groups. These effects correlated well with reduced stress levels, as indicated by lower facial grimace scores in the tube-lifted groups than in the tail-lifted group. Handler interaction, after repeated blood sampling, was highest in the habituated group, and only the habituated group voluntarily climbed on the handler after blood sampling. Our results indicate that stress caused by tail lifting, oral gavage, and blood sampling results in reduced drug uptake and exposure. This stress can be reduced by gentle handling and habituation, which may result in more relevant pharmacokinetic data, increased scientific quality, and improved animal welfare.