Pharmacokinetics of an extended-release formulation of eprinomectin in healthy adult alpacas and its use in alpacas confirmed with mange.

The study objective was to determine the pharmacokinetics and clinical effects of an extended-release 5% eprinomectin formulation (Longrange((R))) following subcutaneous (s.c.) injection in healthy (n=6) and mange-infected (n=4) adult alpacas. High-performance liquid chromatography was used to analyze plasma samples obtained at regular intervals for 161days following a single 5mg/kg injection s.c. in healthy alpacas, and for 5days following each dose (3 treatments, 2months apart) in mange-affected animals. Skin scrapings and biopsies were performed pre- and post-treatment at two comparable sites in alpacas with mange. Four alpacas served as healthy controls. Eprinomectin plasma concentrations showed a biphasic peak (C-MAX-1: 5.72 +/- 3.25ng/mL; C-MAX-2: 6.06 +/- 2.47ng/mL) in all animals at 3.88 +/- 5.16days and 77 +/- 12.52days, respectively. Eprinomectin plasma concentrations remained above 1.27 +/- 0.96ng/mL for up to 120days. Hematocrit (35.8 vs. 31.3%, P<0.003) and albumin (3.5 vs. 2.8g/dL P<0.006) reduced significantly over 6months in multidose animals, while fecal egg counts did not differ between groups. Self-limiting injection site reactions occurred in 9 of 10 animals. Pre- and post-treatment skin biopsies showed reduced hyperkeratosis, but increased fibrosis, with 1 of 4 alpacas remaining positive on skin scraping for mange. In conclusion, alpacas require a higher eprinomectin dose (5.0mg/kg s.c.) than cattle, to reach comparable plasma concentrations.