Pharmacokinetics of Single-Dose Selamectin Administered Topically in American Bullfrogs (Rana catesbeiana)
Parasitism is frequently encountered in captive amphibians and may cause significant morbidity and mortality.2 Information regarding the use and efficacy of currently available anthelmintics in amphibians is limited.4 Unfortunately, the usual routes of oral or parenteral administration of anthelmintics to amphibians can be difficult, especially in small individuals and those that reside in large groups. Selamectin has been shown to have a wide safety margin in mammals and is effective against several different types of parasites.1,3 Since frogs readily absorb substances through the skin, cutaneous administration of selamectin would be easy to administer and may prove useful in controlling amphibian parasites. In this study, 32 American bullfrogs were randomly assigned to eight groups with four animals in each group. One group served as the pretreatment control, and frogs in the seven other groups each received 6 mg/kg selamectin by topical administration to the skin on the back. Each group was randomly selected for sampling on days 1, 5, 10, 15, 20, 25, and 30. On these days, the frogs in the assigned group were euthanatized, and plasma samples were obtained. Lung, liver, kidney, and skin sections were collected for histology. There were no adverse drug effects and no signs of toxicity on histologic analysis of tissues. The plasma samples were analyzed to obtain pharmacokinetic data and determine a potential therapeutic dosage for amphibians.
1. McTier, T.L., J.A. Hair, et al. 2003. Efficacy and safety of topical administration of selamectin for treatment of ear mite infestation in rabbits. J. Am. Vet. Med. Assoc. 223:322–324.
2. Poynton, S.L., and B.R. Whitaker. 2001. Protozoa and metazoa affecting amphibians. In: Wright K.M., Whitaker B.R. (eds.). Amphibian Medicine and Captive Husbandry. Krieger Publishing Co., Malabar, Florida. Pp: 193–221.
3. Sarasola, P., A.D. Jernigan, et al. 2002. Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs. J. Vet. Pharmacol. Therap. 25:265–272.
4. Wright, K.M., and B.R. Whitaker. 2001. Pharmacotherapeutics. In: Wright K.M., Whitaker B.R. (eds.). Amphibian Medicine and Captive Husbandry. Krieger Publishing Co., Malabar, Florida. Pp: 309–330.