Nontraditional pets are rapidly becoming an integral part of many companion animal practices, and more households report owning rabbits than any other exotic mammal.1 In addition, the amount of financial resources that owners are spending on rabbit care is also increasing.1
Lack of pharmacokinetic, efficacy, and safety data for chemotherapeutics in small mammals can be very problematic because veterinarians may need to use agents approved for other species and extrapolate their safety and efficacy to small mammals without a scientific basis. The rate and extent of absorption as well as the rate of elimination and persistence of drugs after administration to small mammals such as rabbits are often unknown, making safe and effective dose recommendations difficult. Although the safety, efficacy, and pharmacokinetic parameters for numerous pharmaceutical agents have been reported for more traditional domestic animal species, data are needed to ensure proper dosing and treatment of other species for which approved drugs are not available.
Selamectina is a macrocyclic lactone of the avermectin subclass. It is a safe, broad-spectrum endectocide approved for topical use at doses of 6 to 12 mg/kg in cats and dogs.2 Transdermal absorption of selamectin following topical administration in dogs and cats rapidly results in plasma concentrations of the drug, and plasma and tissue concentrations are sustained for several weeks after administration.3 Selamectin is approved for use in killing adult fleas and preventing eggs from hatching for ≥ 1 month in dogs and cats.2 In controlled studies,4 > 98% of fleas were killed within 36 hours after application, and in field studies,5 1 application of selamectin resulted in > 90% reduction in mean flea counts 30 days after administration. Selamectin is also approved for prevention of heartworm disease caused by Dirofilaria immitis and for treatment and control of ear mites (Otodectes cynotis) in dogs and cats. Other approved uses include elimination of roundworm (Toxocara cati) and intestinal hookworm (Ancylostoma tubaeforme) infections in cats, and treatment and control of sarcoptic mange (Sarcoptes scabei) and control of tick infestations caused by Dermacentor variabilis in dogs. In addition, selamectin effectively controls lice6 and Cheyletiella spp7,8 in dogs and cats.
Results of 1 efficacy study9 revealed that topical application of selamectin at a dose of 6 or 18 mg/kg eliminated ear mites (Psoroptes cuniculi) in rabbits. Other reports describing the topical use of selamectin in rabbits indicated that it was effective against P cuniculi and S scabei at doses of 6 to 18 mg/kg,10 S scabei at doses of 8 to 14 mg/kg,11 Cheyletiella parasitovorax at doses of 6.2 to 20 mg/kg (1 to 3 times with an interval of 2 to 4 weeks between treatments)12 or 12 mg/kg (as a single dose),13 and Cheyletiella spp and Leporacaerus gibbus at a dose of 15 mg for rabbits that weighed < 2.3 kg or 45 mg for those that weighed ≥ 2.3 kg.14 Selamectin was recommended for treatment against fleas in rabbits at a dose of 18 mg/kg (repeated 30 days later if needed).15 The extralabel use of this drug for treatment of ectoparasites and some endoparasites in a variety of small mammals (including rabbits) and birds has been reviewed elsewhere.16
Ctenocephalides felis or Ctenocephalides canis (common cat and dog fleas, respectively) are the fleas most typically found on pet rabbits, and these infestations can result from living in shared environments with cats and dogs.17 Infestation causes intense pruritis, and allergic dermatitis can develop. Although no ectoparasiticide is currently licensed for use in rabbits in the United States, selamectin, imidacloprid (flea adulticide), lufenuron (flea ovicide and larvacide), carbaryl powder, and pyrethrins have been used to control fleas in rabbits.17,18 However, to the authors' knowledge, no pharmacokinetic or safety studies of these products have been performed in rabbits.
The objective of the study reported here was to determine pharmacokinetics, efficacy, and adverse effects of selamectin administered topically at doses of 10 or 20 mg/kg in rabbits infested with a predetermined quantity of fleas. We also sought to identify treatment intervals at which these doses of selamectin would maintain effective flea control in rabbits.
Area under the plasma concentration-versus-time curve from time 0 through infinity
Maximum plasma concentration
Fraction of absorbed dose
Lower limit of quantification
Mean residence time
Time to reach maximum plasma concentration
Volume of distribution determined by use of the area method
Revolution, Pfizer Animal Health, New York, NY.
Bunny basics 15/23, Oxbow Pet Products, Murdock, Neb.
Western Timothy Hay, Oxbow Pet Products, Murdock, Neb.
Shimadzu Prominence, Shimadzu Scientific Instruments, Columbia, Md.
API 2000, Applied Biosystems, Foster City, Calif.
Bond Elut C18, Varian, Palo Alto, Calif.
Supelco Discovery, 50 × 2.1 mm, 5 μm, Sigma-Aldrich, St Louis, Mo.
WinNonlin 5.2, Pharsight Corp, Mountain View, Calif.
SigmaStat, version 3.11, Systat Software Inc, San Jose, Calif.
Sarasola P, Jernigan AD, Walker DK, et al. Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs. J Vet Pharmacol Ther 2002; 25:265–272.
McTier TL, Shanks DJ, Jernigan AD, et al. Evaluation of the effects of selamectin against adult and immature stages of fleas (Ctenocephalides felis felis) on dogs and cats. Vet Parasitol 2000; 91:201–212.
Boy MG, Six RH, Thomas CA, et al. Efficacy and safety of selamectin against fleas and heartworms in dogs and cats presented as veterinary patients in North America. Vet Parasitol 2000; 91:233–250.
Chailleux N & Paradis M. Efficacy of selamectin in the treatment of naturally acquired cheyletiellosis in cats. Can Vet J 2002; 43:767–770.
McTier TL, Hair JA, Walstrom DJ, et al. Efficacy and safety of topical administration of selamectin for treatment of ear mite infestation in rabbits. J Am Vet Med Assoc 2003; 223:322–324.
Kurtdede A, Karaer Z, Acar A, et al. Use of selamectin for the treatment of psoroptic and sarcoptic mite infestation in rabbits. Vet Dermatol 2007; 18:18–22.
Farmaki R, Koutinas AF, Papazahariadou MG, et al. Effectiveness of a selamectin spot-on formulation in rabbits with sarcoptic mange. Vet Rec 2009; 164:431–432.
Mellgren M & Bergvall K. Treatment of rabbit cheyletiellosis with selamectin or ivermectin: a retrospective case study. Acta Vet Scand 2008; 50:1–6.
Kim S-H, Lee J-Y, Jun H-K, et al. Efficacy of selamectin in the treatment of cheyletiellosis in pet rabbits. Vet Dermatol 2007; 19:26–27.
Van Praag E. Parasites affecting rabbits: fleas. Available at www.medirabbit.com/EN/Skin_diseases/Parasitic/fleas/Fleas.htm. Accessed June 15, 2010.
Fisher M, Beck W, Hutchinson MJ. Efficacy and safety of selamectin (Stronghold/Revolution) used off-label in exotic pets. Int J Appl Res Vet Med 2007; 5:87–96.