The patient population was recruited from cats at least eight weeks of age and at least 1.25 kg bodyweight. There were no breed or gender restrictions, however pregnant females or cats intended for breeding were not eligible for enrollment.

Cats with a history of apparent reactions to products containing selamectin or sarolaner were excluded from enrollment, as were cats that had been treated with an ectoparasiticide with residual efficacy against N. cati mites at the time of enrollment.

In case of multi-cat households, the cat with the most severe clinical signs of notoedric mange was the primary patient (used for efficacy and safety evaluations) and all other cats in the same household were considered supplementary patients (used for safety evaluations only).

Skin scrapings for detection of live N. cati mites were conducted on Days 0, 30, and 60. Deep scrapings were taken from the three body areas that showed the most severe or most likely clinical signs of infestation. Scrapings were performed over an area of approximately 1 cm² to an approximately consistent depth. The collected material was transferred to mineral oil on a microscope slide and live N. cati mites (larvae, nymphs, and adults) and any eggs present were counted using 40X magnification.

Clinical signs of notoedric mange were assessed before skin scraping and treatment on each mite count day. Each cat was thoroughly examined for skin lesions characteristic of notoedric mange including crusting, erythema, hair loss, papules, pruritus, pustules, and scaling. The severity of each clinical sign was scored as absent (no observable abnormality); mild (intensity/density is low and only a small area is affected); moderate (great intensity/density over a small area or of lesser intensity/density but affecting a large area); and severe (great intensity/density and covers a large area).

Primary cats were allocated to one of the two treatments according to a randomized complete block design. Cats were blocked based on order of enrolment in groups of two and each cat allocated randomly to treatment with either placebo or Stronghold Plus (selamectin + sarolaner) within the block. Any supplementary cats in the household received the same treatment as the primary cat.

Treatment was administered on Days 0 and 30 by the Dispenser (masked study personnel not involved in any efficacy and safety assessments). Doses were calculated based on the body weight of the cats collected immediately prior to each dosing.

Cats allocated to the control group were treated with 0.5 mL of paraffin oil. Cats allocated to the treated group were treated with commercial Stronghold Plus according to the approved product label directions which provided 6.0 to 12.0 mg/kg selamectin and 1.0 to 2.0 mg/kg sarolaner.

Treatments were applied topically at the base of the cat’s neck in front of the shoulder blades. The cat’s hair was parted and the treatment applied directly to the exposed skin. Each cat was observed for approximately one minute after dosing to confirm that there was no loss of the administered treatment due to run-off.

Physical examinations were performed by a suitably trained veterinarian on all cats prior to the first treatment administration on Day 0, and again on Days 30 and 60. All abnormal health events observed by the veterinarian during physical examinations or observed by the owner were recorded, as were any concomitantly administered medications. In addition, two days after each treatment administration (i.e., on Days 2 and 32) the treatment administration site was examined by a veterinarian for abnormalities including matting of the hair, spiking/stiff hair, wetness, white deposits, alopecia, erythema, and edema.

All cats that received treatment were included in the safety assessments and only primary cats were included in the efficacy analyses. The primary cat in each household was the experimental unit and the primary endpoint was the total live N. cati mite count, which was calculated by adding together all live larvae, nymphs, and adults collected from the scraped sites on each cat.

The primary efficacy evaluation was determined based on the total live mite counts for the Stronghold Plus-treated cats relative to placebo on Day 30. Total live mite counts on Day 30 were analyzed using a general linear mixed model. The fixed effect was treatment, and the random effect was error. Treatment least squares means, standard errors, 95% confidence intervals, and minimums and maximums were calculated. Percent effectiveness of Stronghold Plus relative to placebo was calculated using least squares means based on the formula [(C-T)/C] x 100, where C = mean live mite count for the placebo group, T = mean live mite count for the treated group.

Secondary efficacy evaluations included comparisons of the total live mite counts on Day 60 compared to Day 0 for both treatment groups, and parasitological cure (no live mites found) on Days 30 and 60 for both treatment groups. Total live mite counts on Days 0 and 60 were analyzed by treatment group using a general linear mixed model. The fixed effect was time point, and the random effect was error. Treatment least squares means, standard errors, 95% confidence intervals, and minimums and maximums were calculated. Percent reduction on Day 60 compared to Day 0 was calculated for each treatment group using least squares means based on the formula [(Day 0-Day 60)/Day 0] x 100, where Day 0 = mean live mite count for Day 0, and Day 60 = mean live mite count for Day 60. Parasitological cure Yes/No on Days 30 and 60 was analyzed using Fisher’s Exact test by day as a generalized linear model failed to converge.

Mite egg counts were summarized by adding together all eggs collected from all scraped sites at each timepoint. Egg mite counts were not analyzed as they did not represent a measure of the presence of live mites at that time point.

Twenty primary cats (10 placebo and 10 Stronghold Plus) were enrolled and treated (Table 1). None of the primary cats lived in multi-cat households, therefore no supplementary cats were enrolled. All enrolled cats completed the entire study and data from all cats were included in all efficacy and safety evaluations.

No adverse health events were observed in any cat during the study. The only concomitant medications administered during the study were ketamine hydrochloride, xylazine hydrochloride, and atropine used for the sedation of one Stronghold Plus-treated cat for the skin scraping performed on Day 0.

There were no incomplete dosing events and thus all cats received a complete dose of either placebo or Stronghold Plus at the base of the neck in front of the shoulder blades on Days 0 and 30. Two days after each treatment, the administration sites for all placebo and Stronghold Plus-treated cats were normal with no signs of hair matting, spiking/stiff hair, wetness, white deposits, alopecia, erythema, or edema observed in any cat.

On Day 0, live mite counts ranged from 6–26 (least squares mean 11.7) in the placebo group and from 9–15 (least squares mean 10.8) in the Stronghold Plus-treated group (Table 2 and Figure 2).

On Day 30, all placebo-treated cats remained mite infested (range 8–16; least squares mean 11.4) while none of the Stronghold Plus-treated cats harbored any live mites. Thus, a single dose of Stronghold Plus provided a significant (p < 0.0001) reduction of 100% in live N. cati mites relative to placebo within 30 days after treatment.

On Day 60, all placebo-treated cats remained mite infested (range 3–15; least squares mean 9.0) while none of the Stronghold Plus-treated cats harbored any live mites. Relative to Day 0, live mite counts in the placebo group were reduced by 23.1% but were not significantly (p = 0.1962) lower than on Day 0. In contrast, live mite counts in the Stronghold Plus-treated group were reduced by 100% and were significantly (p < 0.0001) lower than on Day 0.

Live N. cati mites were found on all placebo-treated cats on Days 30 and 60, while no live mites were found on any Stronghold Plus-treated cat on either day. Parasitological cure (no live mites found) on Days 30 and 60 for the Stronghold Plus-treated group was thus 100% and significantly different from the placebo group on both days (p < 0.0001) (Table 3).

On Day 0, N. cati eggs were found on all placebo-treated cats (range 1–4) and on nine of the Stronghold Plus-treated cats (range 0–6) (Table 2). On Days 30 and 60, mite eggs were found on nine and six of the placebo-treated cats, respectively, while no eggs were found on any of the Stronghold Plus-treated cats on either Day.

On Day 0, the percentage of cats with clinical signs of notoedric mange in both treatment groups were identical with 10% of cats having pustules, 70% having papules, and 100% having crusting, erythema, hair loss, pruritus, and scaling (Table 4). In the placebo group the clinical signs remained stable throughout the study with 30% of cats having pustules, 80% having papules, and 100% having crusting, erythema, hair loss, pruritus, and scaling on Day 30, and 40% of cats having pustules, 80% having papules, and 100% having crusting, erythema, hair loss, pruritus, and scaling on Day 60. In the Stronghold Plus-treated group clinical signs improved with no cats having crusting, papules, or pustules, 10% having erythema and scaling, 20% having pruritus, and 70% having hair loss on Day 30, and no clinical signs of notoedric mange were present in any Stronghold Plus-treated cat on Day 60.