Toxicity and Pharmacokinetic Studies of Lidocaine and Its Active Metabolite, Monoethylglycinexylidide, in Goat Kids

SIMPLE SUMMARY: Disbudding is becoming a routine husbandry procedure in goat farms even though it is a painful procedure without appropriate pain relief. One of the ways to alleviate or minimize the pain associated with disbudding is by using local anesthetics like lidocaine hydrochloride. However, lidocaine hydrochloride has been reported to be toxic in goat kids and there is some data regarding the doses that produce toxicity in goat kids. Therefore, the research team studied the toxicity and pharmacokinetics of lidocaine hydrochloride in goat kids to recommend a safe dose for disbudding. ABSTRACT: This study determined the convulsant plasma concentrations and pharmacokinetic parameters following cornual nerve block and compared the results to recommend a safe dose of lidocaine hydrochloride for goat kids. The plasma concentrations of lidocaine and monoethylglycinexylidide (MGX) were quantified using liquid chromatography-mass spectrometry. A total dose of 7 mg/kg body weight (BW) was tolerated and should therefore be safe for local and regional anesthesia in goat kids. The mean plasma concentration and mean total dose that produced convulsions in goat kids were 13.59 ± 2.34 µg/mL and 12.31 ± 1.42 mg/kg BW (mean ± S.D.), respectively. The absorption of lidocaine following subcutaneous administration was rapid with C(max) and T(max) of 2.12 ± 0.81 µg/mL and 0.33 ± 0.11 h, respectively. The elimination half-lives (t(½λz)) of lidocaine hydrochloride and MGX were 1.71 ± 0.51 h and 3.19 ± 1.21 h, respectively. Injection of 1% lidocaine hydrochloride (0.5 mL/site) was safe and effective in blocking the nerves supplying horn buds in goat kids.