Since 2019, there has been a discontinuation in the distribution of pharmaceutical-grade pentobarbital and secobarbital in Japan, as well as a global shortage of the drugs in the rest of the world. This shortage impacts laboratory animal facilities as they are commonly used for euthanasia through overdose. Therefore, there is a need for a new, effective, injectable euthanasia drug protocol that reliably and safely replaces pentobarbital and secobarbital (SB). A study in Experimental Animals compares a combination of medetomidine, midazolam and butorphanol (MMB), as well as a newer formulation in which midazolam is replaced with alfaxalone (MAB), as replacements for the previously used euthanasia drugs.

The team compared MAB and MMB with SB as a control euthanasia agent. None of the MMB animals experienced cardiac arrest within 30 minutes, ruling out this combination as an euthanasia agent. Results show that at comparable doses, alfaxalone alone did not induce death. Males from both the SB and MAB groups took longer to reach cardiac arrest compared with females, showing a sexually dimorphic response to the drugs. The team further compared MAB and SB to better evaluate the potential of MAB. Achieving a loss of righting reflex and respiratory arrest was faster in the MAB group compared to SB, but cardiac arrest happened at the same time. Cardiac function suppression was more pronounced in the MAB group compared to SB. Analysis of serum biochemical parameters revealed no differences between euthanasia protocols. While MAB's acidic pH (4.9) may raise concerns about injection-related tissue irritation, its components are veterinary-approved and generally more accessible than human-use barbiturates.

This study not only identifies MAB as a viable barbiturate-free euthanasia agent but also removes MBB as an alternative. The study also highlights the importance of identifying alternative protocols amid drug shortages. Future studies should investigate the mechanisms behind alfaxalone and medetomidine's synergistic lethal effects. However, MAB seems to be a reliable alternative to SB.

Original reference: Kiyoto, M. et al. Exp. Anim. https://doi.org/10.1538/expanim.25-0052 (2025)