IV Lidocaine for Analgesia in Anesthetized Cats

In the Literature

Comassetto F, Serighelli Júnior G, Iepsen LB, Cavagnari CFB, Oleskovicz N. Intravenous lidocaine may contribute to postoperative analgesia without detectable adverse effects in cats undergoing ovariohysterectomy: a randomized trial. J Am Vet Med Assoc. 2025;264(3):297-304. doi:10.2460/javma.25.05.0343

The Research …

IV lidocaine provides analgesia and reduces opioid requirements in several species (eg, dogs, rabbits, horses, humans).^1-4 Although IV lidocaine is often avoided in cats due to concerns for increased sensitivity to local anesthetics,^5,6 studies have suggested that the most commonly used clinical dose of lidocaine (2 mg/kg) may be administered to cats without inducing signs of toxicosis.^7,8

This study evaluated the analgesic effects of an IV lidocaine infusion in cats undergoing routine ovariohysterectomy and assessed for signs of lidocaine toxicosis using clinically relevant doses. The study included healthy female cats (n = 24) that were randomly assigned to a lidocaine group (2 mg/kg IV lidocaine bolus followed by continuous lidocaine infusion [3 mg/kg/hour]), bolus-only group (2 mg/kg IV lidocaine bolus followed by continuous saline infusion), or control group (equal volume saline bolus followed by continuous saline infusion). All cats were anesthetized for routine ovariohysterectomy, and physiologic variables were monitored. Postoperative pain assessment using a validated feline pain scale was performed at regular intervals for 24 hours. Intra- and postoperative rescue analgesia was provided when indicated. Cats were also monitored for signs of lidocaine toxicosis (eg, tremors, hypersalivation, vomiting, bradyarrhythmia) peri- and postoperatively.

Requirements for end-tidal isoflurane concentrations were significantly lower in the lidocaine group compared with the control group, and significantly fewer administrations of postoperative morphine rescue analgesia were needed in the lidocaine group compared with the other 2 groups. No clinically significant differences in cardiovascular or respiratory variables or in time to extubation or ambulation were found among the groups. No signs of lidocaine toxicosis were observed in any cat during the peri- or postoperative periods.

… The Takeaways

Key pearls to put into practice:

• In this study, lidocaine (2 mg/kg IV bolus or 3 mg/kg/hour continuous infusion) reduced isoflurane requirements and provided analgesia in healthy cats undergoing routine ovariohysterectomy without evidence of systemic toxicosis.

• Neurologic signs of local anesthetic toxicosis (eg, excitation, agitation, nystagmus, respiratory depression) are often expressed prior to cardiovascular signs of toxicosis and may be difficult to discern in anesthetized patients, resulting in late-stage recognition of toxicosis.

• This study suggests lidocaine may be administered to cats at clinically relevant doses (2 mg/kg) for local and regional anesthetic techniques that typically result in minimal systemic absorption of lidocaine.

• General anesthesia can affect the pharmacodynamics of lidocaine in cats.⁸ In another study, anesthetized cats administered the same bolus dose of lidocaine used in this study had higher initial plasma concentrations and significantly decreased clearance compared to awake cats, likely due to decreased cardiac output, hepatic blood flow, and hepatic clearance associated with general anesthesia. The current study evaluated use of continuous infusion for a total of 60 minutes and showed no evidence of systemic toxicosis or delayed recovery; however, it is unclear whether longer infusions would be similarly well tolerated.

• IV lidocaine administration at doses reported in this study appears safe in healthy cats, but due to the narrow therapeutic window and concern for severity of toxicosis, consideration is needed on whether lidocaine toxicosis can be treated at the clinic prior to multimodal feline analgesia.