Lidocaine hydrochloride is widely used in veterinary practice for complete block of sensory nerves. It appears to have additional analgesic activity when administered via many routes. It has been used intraperitoneally (IP) in humans for years to provide intraoperative and postoperative analgesia for abdominal surgery, and dogs receiving lidocaine after ovariohysterectomy have tended to show lower pain scores. In this study, 6 mixed-breed, female dogs were given a conservative dose (8 mg/kg IP with epinephrine 1:400,000, and 2 mg/kg topical incisional with epinephrine 1:200,000) following ovariohysterectomy. Maximum plasma levels of lidocaine were determined; pharmacokinetic variables were determined from plasma concentration data; and safety was confirmed, as toxic effects are directly proportional to the amount of drug administered and plasma concentration. Rapid uptake of lidocaine via the 2 administration routes produced peak plasma concentrations of 1.45 ± 0.36 mg/ml (mean ± SD, 0.08 to 1.86 mg/ml) by 0.37 ± 0.1 hour after surgery (range 0.11 to 0.81 hr)-about half the levels reported as therapeutic in previous studies in dogs and well below toxic levels. The drug had a half-life of 1.17 ± 0.11 hour, and no signs of toxicity were observed in any of the patients in the 18 hours following administration. Although it seems likely that the local effect provides the analgesia, further dose-response studies would be useful.
COMMENTARY: Local blocks are so easy to do that any vet could enhance postoperative pain management of a simple spay or other abdominal procedure, yet I bet only a handful think to do it. Lidocaine is inexpensive, and this study has shown that in sensible doses it is nontoxic as well: easy, inexpensive, safe.
Pharmacokinetics of combined intraperitoneal and incisional lidocaine in the dog following ovariohysterectomy. Wilson DV, Barnes KS, Hauptman JG. J VET PHARMACOL THER 27:105-109, 2004.