The Pharmacokinetics and Pilot Efficacy of Levamisole Administered by Subcutaneous Injection of a Combination Product in Domestic Goats (Capra aegagrus hircus)

Anthelmintic resistance is a major welfare issue in goats, and the efficacy of anthelmintic drugs lies in judicious use. Recently, an injectable combination (levamisole-doramectin) product labeled for cattle became available. This study’s goal was to compare the levamisole pharmacokinetic parameters of this new combination drug to a commercially available oral levamisole formulation in goats. Six adult goats subcutaneously received a 9 mg/kg dose of the combination product. Blood samples were collected at 14 time points over 48 hours. After a 14-day washout period, the same goats were given 12 mg/kg of oral levamisole and sampled following the same time points. Levamisole concentrations were measured via liquid chromatography. A non-compartmental analysis was used to generate pharmacokinetic (PK) parameters for both formulations. After one subcutaneous (SC) injection, the maximum plasma concentration (C_max), time to C_max (T_max), area under the curve (AUC), and elimination half-life (T_1/2) was 468.57 ± 151.12 ng/mL, 2.24 ± 1.58 hours, 3206.42 ± 1189.73 h*ng/mL, and 2.36 ± 2.07 hours, respectively. After a single oral administration, C_max, T_max, AUC, and T_1/2 were 573.21 ± 149.01 ng/mL, 0.5 ± 0.41 hours, 2995.47 ± 2203.93 h*ng/mL, and 3.74 ± 2.19 hours, respectively. Fecal samples taken before and after subcutaneous administration had an average egg count reduction of 61.97% (P = 0.0625). The relative bioavailability of the SC injection was 185%. Considering bioavailability and egg count reduction, the combination product may be considered for parasite management, however, a field trial is needed to determine its efficacy and other pharmacodynamic parameters.