Euthanasia of canines and felines under anesthesia can be achieved with lidocaine or mepivacaine via intrathecal, intravenous, or intracardiac routes.

Objective: To determine the effectiveness of lidocaine (L) and mepivacaine (M) as euthanasia agents in canine and feline patients via intrathecal (ITh), intravenous (IV), and intracardiac (IC) routes following induction of general anesthesia.

Methods: Canine and feline patients were euthanized from April 2024 through September 2024 at an animal shelter. Patients were randomly selected as part of an experimental study to receive L or M into the spinal subarachnoid space (ITh) or by IV or IC injection. Time to death and active signs of dying were recorded.

Results: A total of 54 canines and 66 felines were euthanized. Canines: mean time (± SD) to death (cardiac standstill) from ITh administration was 313.0 ± 74.4 seconds (L) and 261.4 ± 28.9 seconds (M); mean time to death from IV or IC administration was 203.8 ± 77.6 seconds (L) and 212.5 ± 37.8 seconds (M). Felines: mean time to death from ITh administration was 245.8 ± 65.0 seconds (L) and 311.0 ± 100.4 seconds (M); mean time to death after IV or IC administration was 98.9 ± 58.8 seconds (L) and 123.2 ± 86.6 seconds (M).

Conclusions: L and M cause death in anesthetized canine and feline patients when administered at lethal doses (4 mg/kg ITh and 28 mg/kg, IV or IC). The ITh route took longer to achieve death in both species but had reduced active signs of death.

Clinical relevance: L and M may be used as alternative euthanasia agents when pentobarbital sodium is unavailable or undesired.