Intraperitoneal Injection of Ethanol for the Euthanasia of Laboratory Mice (Mus musculus) and Rats (Rattus norvegicus)

Compassion, professional ethics, and public sensitivity require that animals are euthanized humanely and appropriately under both planned and emergent situations. According to the 2013 AVMA Guidelines for the Euthanasia of Animals, intraperitoneal injection of ethanol is "acceptable with conditions" for use in mice. Because only limited information regarding this technique is available, we sought to evaluate ethanol by using ECG and high-definition video recording. Mice (n = 85) and rats (n = 16) were treated with intraperitoneal ethanol (70% or 100%), a positive-control agent (pentobarbital-phenytoin combination [Pe/Ph]), or a negative-control agent (saline solution). After injection, animals were assessed for behavioral and physiologic responses. Pain-assessment techniques in mice demonstrated that intraperitoneal injection of ethanol was not more painful than was intraperitoneal Pe/Ph. Median time to loss of consciousness for all mice that received ethanol or Pe/Ph was 45 s. Median time to respiratory arrest was 2.75, 2.25, and 2.63 min, and time (mean ± SE) to cardiac arrest was 6.04 ± 1.3, 2.96 ± 0.6, and 4.03 ± 0.5 min for 70% ethanol, 100% ethanol, and Pe/Ph, respectively. No mouse that received ethanol or Pe/Ph regained consciousness. Although successful in mice, intraperitoneal ethanol at the doses tested (9.2 to 20.1 g/kg) was unsuitable for euthanasia of rats (age, 7 to 8 wk) because of the volume needed and prolonged time to respiratory effects. For mice, intraperitoneal injection of 70% or 100% ethanol induced rapid and irreversible loss of consciousness, followed by death, and should be considered as "acceptable with conditions."