Drug Residues after Intravenous Anesthesia and Intrathecal Lidocaine Hydrochloride Euthanasia in Horses

Abstract

BackgroundIntrathecal lidocaine hydrochloride under general anesthesia has been used as an alternative method of euthanasia in equids. Carnivore, scavenger, and even human consumption of horse meat from carcasses have been anecdotally reported in rural areas after this method of euthanasia. The presence of drug residues in horse meat has not been investigated.Hypothesis/ObjectivesTo investigate if drug residues are found in horse tissues and determine their concentrations.AnimalsOf 11 horses requiring euthanasia for medical reasons.MethodsProspective descriptive study. Horses were anesthetized with total IV dose of xylazine (mean, 2.5 mg/kg), midazolam (0.1 mg/kg), and ketamine hydrochloride (mean, 5.8 mg/kg). An atlanto‐occipital cisterna centesis for the collection of cerebrospinal fluid (CSF) and administration of lidocaine hydrochloride (4 mg/kg) was performed. Blood samples for both serum and plasma, skeletal muscle (triceps brachii, gluteus medius), and CSF were collected for the determination of drug residues. Frozen skeletal muscle available from 5 additional horses that received standard dosages of drugs for short‐term anesthesia (xylazine 1.1 mg/kg, midazolam 0.1 mg/kg, and ketamine 2.2 mg/kg) also were analyzed.ResultsDrug residues were found in the tissues of all horses, but at extremely low concentrations.Conclusions and Clinical ImportanceEuthanasia by administration of lidocaine intrathecally to horses under IV anesthesia poses a low risk of toxicity to carnivores and scavengers that might consume muscle tissue from a carcass in which this protocol has been used.

Use of potassium chloride for low-residue euthanasia of anesthetized California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris) with life-threatening injury or disease

“…In other studies, postmortem gross and histologic artifacts caused by administration of KCl are reported to be subtle to absent. 10,28,29 Raghav et al 10 found no histologic artifacts in 12 psittacine birds euthanized with KCl. Coulibaly et al 27 identified whitish crystallized deposits on internal organs on gross examination and rare crystalline bundles on histologic examination of 2 human fetuses after medical termination of pregnancy with the use of KCl.…”

“…Harms et al 6 measured tissue concentrations of midazolam, acepromazine, and xylazine in mysticete whales following euthanasia and concluded that of these, only xylazine posed a potential risk of relay intoxication of scavengers. Aleman et al 29 measured tissue concentrations of xylazine, midazolam, ketamine, and lidocaine in horses following euthanasia and detected levels that could cause sedation in scavengers that consumed sufficient quantities of tissue. Thus, when a carcass of a treated animal is to remain in situ, local removal of its skin, blubber, and muscle at sites of intramuscular injections may be considered to prevent scavenger intoxication and environmental contamination.…”

Intrathecal mepivacaine after general anesthesia is an effective method of equine euthanasia when compared to intravenous pentobarbital

“…Previous publications have shown that the risk of scavenger intoxication through consumption of the carcass is low with an intrathecal lidocaine method. 7,12 In horses euthanized with intravenous pentobarbital, sodium pentobarbital residues were found in compost pile samples up to 367 days after euthanasia with no decrease in concentration, despite complete degradation of soft tissues. 13 Although drug residues were not examined in this study, it is likely that mepivacaine a short-to medium-duration local anesthetic would have a similar tissue distribution profile to lidocaine, and allow for more options for body disposal and decreased risk of environmental contamination with burial.…”