Efficacy of a Single Dose of an Otic Ivermectin Preparation or Selamectin for the Treatment of Otodectes cynotis Infestation in Naturally Infected Cats
ACVIM 2008
L. Nunn-Brooks; R. Michael; L. Ravitz; M.R. Lappin
The Department of Clinical Sciences, Colorado State University
Ft. Collins, CO, USA

Otodectes cynotis infestation is common in kittens housed in crowded environments. Safe, inexpensive, and rapid acting treatments should be used to potentially lessen spread. It is unknown how rapidly O. cynotis is killed within the first 72 hours of treatment. The objective of this study was to describe the speed to kill of a two compounds with known activity against O. cynotis.

Kittens > 4 weeks of age that were shown to have live O. cynotis AU were accepted into the study. Each kitten was administered 0.5 ml of 0.01% Ivermectin otic suspension (Acarexx®, IDEXX Pharmaceuticals), once, AU or selamectin (Revolution®, Pfizer Animal Health) once, on the skin following the manufacturers' instructions. Repeat cytologic examination was performed on individual ears based on a randomization schedule at 6, 12, 24, 36, 48, or 72 hours after treatment. A drug was considered effective if there were dead mites or no evidence of mites on repeat examination.

Dead mites were detected as early as 12 hours after administration of either drug (ivermectin, 2 of 7 ears; selamectin, 2 of 8 ears).

Percentage of ears with dead mites during combined recheck times:

Combined recheck times



6-24 hours

22.2% (4/18)

9.5% (2/21)

36-72 hours

66.7% (12/18)

42.9% (9/21)

Results between groups were not statistically different by Fischer's exact test.

There was no evidence of toxicity noted with either drug. The results suggest that both drugs have an effect against O. cynotis as early as 12 hours after administration with an increasing effect over time.

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Lindsey Nunn-Brooks

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