Moxidectin plasma concentrations following topical administration to llamas (Lama glama) and alpacas (Lama pacos)

Producers and veterinarians commonly administer pharmaceuticals labeled for cattle, sheep, or goats to llamas and alpacas, yet little is known about the safety and efficacy of this extra-label usage. There are many species-related factors, such as bioavailability and metabolism, that could lead to variation in the pharmacokinetic parameters between species and possibly decrease the activity of a compound. This experiment investigated the absorption and disposition of topical (pour-on) moxidectin in llamas and alpacas. Seven llamas and seven alpacas were obtained from commercial sources and were not treated with an avermectin/milbemycin agent within 60 days prior to the start of the study. The animals were housed outdoors with water and hay available ad libitum. All animals received moxidectin at a dose of 500 g/kg after being clipped along the dorsal midline. Serial blood samples were collected post dose. Samples were analyzed for moxidectin using a validated liquid chromatography/mass spectroscopy assay. Moxidectin administration was well tolerated with no adverse effects noted in either species following topical administration. Median Cmax values were highly variable in the llamas and alpacas with two alpacas having no detectable plasma concentrations of moxidectin. Due to the limited absorption of this compound in both species, appropriate pharmacokinetic parameters could not be determined. In these two species of South American camelids, moxidectin was not well absorbed following topical administration. © 2003 Elsevier B.V. All rights reserved