[Doramectin intoxication in 3 kittens]

Detection of the ABCB11930_1931del TC Mutation in Two Suspected Ivermectin-Sensitive Cats and Their Relatives by a Novel TaqMan Allelic Discrimination Assay

The multidrug resistance gene MDR1 (syn. ABCB1) encodes for the multidrug efflux transporter P-glycoprotein (P-gp), which is highly expressed at the blood-brain barrier and protects the brain from potentially neurotoxic compounds, such as ivermectin. MDR1 mutation in dogs is known to be linked to dramatically increased brain accumulation of ivermectin and life-threatening neurological toxicity. The present report describes two suspected ivermectin-sensitive Maine Coon cats, which exhibited neurological toxicity following subcutaneous application of therapeutic doses of ivermectin. Both cats showed a homozygous 2-bp deletion in the MDR1/ABCB1 coding sequence (ABCB11930_1931del TC, syn. MDR1 nt1930(del2)) that had previously been associated with a drug-sensitive phenotype in cats. For cat MDR1 genotyping, a novel TaqMan allelic discrimination assay was established and validated. This assay was used for ABCB11930_1931del TC genotyping of the drug-sensitive cats as well as of more than 50 relatives. About half of them had the heterozygous MDR1(+/-) genotype, while none of these related cats with former ivermectin treatment had a history of drug-sensitivity. In conclusion: The present study supports previous findings on drug-sensitivity in cats with homozygous ABCB11930_1931del TC mutation. The newly established TaqMan allelic discrimination assay provides a useful and reliable method for routine MDR1 genotyping in cats in order to identify drug-sensitive cats prior to treatment with established P-gp substrates such as ivermectin and other macrocyclic lactones and thus to improve therapeutic safety.

Successful treatment of otodemodicosis due to Demodex cati with sarolaner/selamectin topical solution in a cat

Case summary

A 10-year-old spayed female Russian Blue cat was presented with a 3-month history of excessive otic discharge and scratching, only involving the right ear. Other than a moderate amount of ceruminous exudate present within the right ear on video-otoscopic examination, there were no other cutaneous abnormalities. The cat was deemed to be otherwise in good health based on physical examination and several laboratory profiles. A diagnosis of otodemodicosis was determined due to the presence of a large number of Demodex cati mites retrieved from cerumen. Treatment consisted only of monthly topical application of sarolaner/selamectin to the nape of the neck with a marked reduction in mite counts and otic pruritus after a single dose. Complete resolution was achieved after a total of four doses.

Relevance and novel information

This is the first report to describe the resolution of mite infestation owing to D cati after treatment with a sarolaner-containing spot-on product. In addition, to the best of the author’s knowledge, this is the first report of any isoxazoline product used in the successful treatment of demodicosis affecting the ear canal. In general, there is a lack of reports describing safe and effective treatments for feline otodemodicosis. Topically applied sarolaner/selamectin resulted in resolution of mites while avoiding any potential ototoxic events from medications applied directly into the ear, and provided a treatment that was easier to apply than oral or injectable macrocyclic lactones.