The efficacy of a novel topical formulation of selamectin plus sarolaner (Revolution® Plus/Stronghold® Plus) in preventing the development of Dirofilaria immitis in cats

Recent Advancements in the Control of Cat Fleas

Simple Summary

The cat flea Ctenocephalides felis felis is the most important pest of domesticated cats and dogs worldwide. This review covers the recent advancements in the control of cat fleas. Over the years, there has been an interest in using ecologically friendly approaches to control fleas. To date, no biological, natural, or cultural means have been discovered that mitigate flea infestations. The recent registration of novel topical and oral therapies promises a new revolution in the control of fleas and ticks and the diseases associated with them.

Abstract

With the advent of imidacloprid and fipronil spot-on treatments and the oral ingestion of lufenuron, the strategies and methods to control cat fleas dramatically changed during the last 25 years. New innovations and new chemistries have highlighted this progress. Control strategies are no longer based on the tripartite approach of treating the pet, the indoor environment, and outdoors. The ability of modern therapies to break the cat flea life cycle and prevent reproduction has allowed for the stand-alone treatments that are applied or given to the pet. In doing so, we have not only controlled the cat flea, but we have prevented or reduced the impact of many of the diseases associated with ectoparasites and endoparasites of cats and dogs. This review provides an update of newer and non-conventional approaches to control cat fleas.

A milbemycin compound isolated from Streptomyces Sp. FJS31-2 with cytotoxicity and reversal of cisplatin resistance activity in A549/DDP cells

Streptomyces Sp FJS31-2 is a strain isolated from special habitat soils in the early stage of our laboratory for producing a new type of halogenated type II polyketide antibiotic with good anti-MRSA activity. In this experiment, a variety of chromatographic and spectroscopic methods was used to isolate and identify a milbemycin compound VM48130 from the ethyl acetate extract of the fermentation products. To investigate its bioactivity, Cell Counting Kit-8 (CCK-8) assay was used to test the cytotoxic activity of the compound against a variety of cancer cells (human liver cancer cell line MHCC97H and SK-Hep1, human nasopharyngeal carcinoma cell line CNE1, mouse melanoma cell line B16, human colon cancer cell line LOVO, human lung adenocarcinoma cell line A549) and normal cells (human bronchial epithelial cell line 16HBE, human normal liver cell line L02, human nasopharyngeal epithelial cell line NP69). The results showed that the compound had significant cytotoxic activity against the above cancer cells, and the IC₅₀ values were 21.96 ± 1.45, 22.18 ± 0.55, 19.42 ± 0.71, 18.61 ± 1.68, 18.62 ± 0.67, 18.52 ± 0.64 μM, respectively. Furthermore, the CCK-8 method was used to evaluate the compound's reversal of cisplatin resistance in multidrug resistant cisplatin-resistant human lung adenocarcinoma (A549/DDP) cells. The results indicated that when the compound concentration was 0.5 μM, the reversal fold (RF) reached 6.25 and showed a dose-dependent effect. At 5 μM, the RF reached 8.35, which was approximately equivalent to the reversal effect of the positive drug verapamil at the same concentration. The expression of MDR1, MRP1, LRP, MAST1 resistance genes and the corresponding proteins were analyzed by quantitative RT-PCR and Western blot assay, and found that the compound could significantly down-regulate the expression of these genes and proteins. These results indicated that VM48130 had the potential of being a lead compound for the treatment or adjuvant treatment of cancer.

The efficacy of a topical formulation of selamectin plus sarolaner in preventing the development of a macrocyclic lactone-resistant strain of Dirofilaria immitis in cats

Revolution®/Stronghold® Plus, a topical endectocide incorporating 6 mg/kg selamectin plus 1 mg/kg sarolaner, is approved for use in cats to prevent heartworm disease. The efficacy of selamectin has not previously been evaluated against any macrocyclic lactone (ML)-resistant heartworm strains in cats for prevention of heartworm disease. In this study, an experimental combination formulation of selamectin (6 mg/kg) plus sarolaner (2 mg/kg) was assessed for preventing the development of a ML-resistant strain of Dirofilaria immitis in cats. Forty purpose-bred domestic shorted-haired cats (20 males; 20 females) from 7-9 months of age and negative for heartworm antigen prior to study inclusion were used. On Day -30, cats were inoculated with 100 D. immitis L₃ (ZoeMO strain) subcutaneously in the inguinal area. Cats were randomly allocated to one of the following four treatments with associated dosing regimens: T01 (vehicle-treated control on Days 0, 28, and 56), T02 (single dose of selamectin plus sarolaner combination on Day 0 only), T03 (selamectin plus sarolaner combination on Days 0, 28, and 56) or T04 (single dose of selamectin on Day 0 only). All treatments were administered topically in an isopropyl alcohol-based formulation. Selamectin was administered at 6 mg/kg in both standalone and combination formulations. Sarolaner was administered at 2 mg/kg. Cats were necropsied on Day ∼145 (∼175 days post infection) and adult worms were counted. Nine of ten cats in the control group (T01) were infected with adult worms (range, 1-23; geometric mean, 3.5). In contrast, all cats in T03 had zero heartworms. Only two cats in T02 (0-3; 0.2) and a single cat in the T04 (0-1; 0.1) had heartworms. Compared to T01 (control cats), all treated cats had significantly (p < 0.0001) reduced worm burdens, with treatment efficacies of 100% (T03), 93.5% (T02) and 98% (T04). A topical combination of selamectin (6 mg/kg) plus sarolaner (2 mg/kg) was 100% efficacious in preventing the development of an ML-resistant strain of D. immitis (ZoeMO) in cats when administered as three consecutive monthly treatments. A single dose was highly (93.5%) but incompletely effective.

Safety and efficacy of a new spot-on formulation of selamectin plus sarolaner in the treatment and control of naturally occurring flea infestations in cats presented as veterinary patients in Australia

Background

The safety and efficacy of a new spot-on formulation of selamectin plus sarolaner were evaluated for the treatment and control of natural flea infestations on cats in two non-randomised, multi-centre clinical trials conducted in 8 different locations in Queensland, Australia.

Methods

One hundred and four cats from 65 different households were enrolled across the two studies. Demographic characteristics of cats in the two studies were similar. The new spot-on formulation of selamectin and sarolaner was administered topically once a month for 3 consecutive months at a minimum dosage of 6 mg/kg selamectin (dose range 6–12 mg/kg) plus 1 mg/kg sarolaner (dose range 1–2 mg/kg). Cats were dosed on Days 0 (pre-treatment), 30 and 60 and physical examinations and flea counts were conducted on Days 0, 30, 60 and 90. Efficacy assessments were based on the percentage reduction in live flea counts post-treatment compared to Day 0.

Results

In Study A, at enrolment, primary cats had flea counts ranging from 6 to 107 (arithmetic mean 21.0). The selamectin and sarolaner spot-on formulation resulted in arithmetic mean efficacy of 98.0%, 100% and 100% on Days 30, 60 and 90, respectively. In Study B, at enrolment, primary cats had flea counts ranging from 6 to 22 (arithmetic mean 10.0). The selamectin and sarolaner spot-on formulation resulted in arithmetic mean efficacy of 99.7%, 100% and 100% on Days 30, 60 and 90, respectively.

Conclusions

The new spot-on formulation of selamectin plus sarolaner topically administered at monthly intervals at the minimum dosage of 6.0 mg/kg selamectin and 1.0 mg/kg sarolaner was safe and highly effective against natural infestations of fleas under a range of geographical conditions, representative of both tropical and subtropical regions of Australia.

Dirofilarioses in cats: European guidelines from the ABCD on prevention and management

OVERVIEW

Dirofilaria immitis and Dirofilaria repens are the most important filarial worms, causing heartworm disease and subcutaneous dirofilariosis, respectively. D repens is currently considered an emerging zoonotic agent in Europe.

LIFE CYCLE AND INFECTION

Filarial worms infect mainly dogs, but also cats, ferrets, wild carnivores and humans. The life cycle involves an intermediate mosquito host. Compared with dogs, cats are imperfect hosts for dirofilarial worms. After inoculation, only a low number of L3 larvae develop to the adult stage in a small percentage of cats. Heartworm disease in cats may be associated with severe pulmonary thromboembolism and an eosinophilic inflammatory response in the lungs, potentially leading to sudden death. Otherwise self-cure occurs in most cases after 18-48 months. Subcutaneous dirofilariosis may present as subcutaneous nodules or dermatitis.

DIAGNOSIS AND TREATMENT

Diagnosis in cats is more difficult compared with dogs and needs a multistep approach (antigen and antibody tests, as well as diagnostic imaging). Cats with acute heartworm disease require stabilisation within an intensive care unit. Cats with respiratory signs or suggestive radiographic changes should receive prednisolone and follow-up with a similar multistep approach. Adulticidal therapy is not safe in cats.

PREVENTION

In endemic areas cats should receive year-round chemoprophylaxis from 2 months of age.

Comparative efficacy of topical treatments with Revolution® Plus (selamectin and sarolaner) and Bravecto® for Cats (fluralaner) against Ixodes scapularis ticks on cats

The efficacy of three consecutive monthly treatments with a novel topical product (Revolution^® Plus/Stronghold^® Plus, Zoetis) containing selamectin in combination with the isoxazoline, sarolaner, was compared with that of another topical isoxazoline, fluralaner [Bravecto^® (fluralaner topical solution) for Cats, Merck] against Ixodes scapularis ticks on cats. Twenty-four cats were ranked by pre-treatment tick counts to form groups of three and were randomly allocated to be treated with placebo, the minimum label dosage of Revolution^® Plus (6 mg/kg selamectin plus 1 mg/kg sarolaner) or the minimum label dosage of Bravecto^® for Cats (40 mg/kg fluralaner) within the groups. On Days 0, 30, and 60, each cat in the placebo and Revolution^® Plus-treated groups was treated topically, whereas cats in the Bravecto^® for Cats-treated group were treated topically once on Day 0 with fluralaner and, subsequently, these animals were treated with the placebo on Days 30 and 60 to maintain masking. Doses were calculated based on weight to provide the minimum label dosage for each product; the calculated volume of product to be administered was rounded off to the nearest 0.1 mL. The selamectin plus sarolaner-treated cats received effective dosages of 5.29-7.12 mg/kg selamectin and 0.88-1.19 mg/kg sarolaner, while the fluralaner cats received dosages of 35.21-43.16 mg/kg fluralaner. Cats were infested with approximately 50 unfed viable adult I. scapularis ticks on Days 5, 12, 26, 40, 54, 68, 82, and 88. Efficacy was assessed at 48 h after each infestation. There were no adverse reactions to any treatment during the study. The placebo-treated cats maintained adequate tick infestations throughout the study. Three monthly treatments with selamectin plus sarolaner (Revolution^® Plus) resulted in high and consistent efficacy against I. scapularis for up to 30 days after each treatment. Based on geometric means, efficacy was ≥99.1% at all time points assessed. Treatment with fluralaner (Bravecto^® for Cats) provided high and consistent efficacy of ≥99.3% up to Day 70. On Day 84, efficacy was 90.1%; however, cats from which ticks were recovered on Day 84 had received approximately 4%-12% less than the minimum dosage of 40 mg/kg fluralaner. Three consecutive monthly treatments with Revolution^® Plus or a single treatment with Bravecto^® for Cats provided >90% control of I. scapularis ticks over a 12-week time period.

Efficacy of three consecutive monthly doses of a topical formulation of selamectin and sarolaner (Revolution® Plus/Stronghold® Plus) compared with a single dose of fluralaner (Bravecto® for Cats) against induced infestations of Ctenocephalides felis on cats

In a controlled laboratory study, the efficacy against fleas, Ctenocephalides felis, of a single treatment of fluralaner topical solution (Bravecto^® for Cats, Merck) was compared with that of three consecutive monthly topical treatments with selamectin and sarolaner (Revolution^® Plus, Zoetis). Twenty-four domestic short hair cats were ranked based on host suitability flea counts to form groups of three and were randomly assigned within group to one of three treatments. The first group received a topical treatment with (a) placebo (vehicle control for Revolution^® Plus) on Days 0, 30, and 60, (b) 6 mg/kg selamectin and 1 mg/kg sarolaner on Days 0, 30, and 60, or (c) 40 mg/kg fluralaner on Day 0 and placebo (vehicle control for Revolution^® Plus) on Days 30 and 60. Because doses were rounded off, the selamectin plus sarolaner-treated cats received effective dosages of 5.25-6.60 mg/kg selamectin and 0.88-1.10 mg/kg sarolaner, while the fluralaner-treated cats received dosages of 34.71-43.08 mg/kg fluralaner. All cats were infested with 100 (±5) fleas on Day -1 and at biweekly intervals after that, from Day 13 to Day 89. Flea comb counts were conducted 24 hours after treatment or after re-infestation. There were no adverse events related to treatment during the study. Except for a single cat from which 20 fleas were recovered on Day 90, all other placebo-treated cats had at least 48 fleas at each count, indicating adequacy of infestation of the controls. Based on geometric mean live flea counts, three consecutive monthly treatments with Revolution^® Plus resulted in consistent and high efficacy of ≥98.6% compared with placebo throughout the study. A single treatment with Bravecto^® for Cats provided consistent and high efficacy of ≥94.6% on all count days during a period of 12 weeks, the approved duration of efficacy for the product. Based on the efficacy results of the study, both products were equivalent in their ability to control fleas on cats. Use of Bravecto^® for Cats every 12 weeks or the consecutive monthly use of Revolution^® Plus is expected to provide extended high residual kill over the respective labeled durations of efficacy of the two products.

Efficacy and safety of a new topical formulation containing selamectin and sarolaner in the prevention of heartworm disease and the treatment of roundworm infection in cats presented as veterinary patients in Japan

The efficacy and safety of a new topical formulation containing selamectin plus sarolaner (Revolution® Plus / Stronghold® Plus, Zoetis) was evaluated for the prevention of heartworm (Dirofilaria immitis) disease and the treatment of roundworm infection in cats enrolled as veterinary patients in two field studies conducted in Japan. In the heartworm field study, 91 cats negative for D. immitis antigen and anti-D. immitis antibody were enrolled and received 9 monthly topical treatments with selamectin plus sarolaner during the period of April to December 2015. Efficacy was assessed by testing post-treatment blood samples collected 8, 12, and 15 months after initiation of treatment for the presence of D. immitis antigen and anti-D. immitis antibody. Eighty-seven cats completed the entire study and were included in the determination of efficacy. No D. immitis antigen or anti-D. immitis antibody were detected in any of the post-treatment samples. In the roundworm field study, completed in the period from April to November 2015, 64 cats with ≥100 roundworm eggs per gram (EPG) of feces were enrolled and allocated randomly in a 1:1 ratio, to receive either selamectin plus sarolaner or emodepside plus praziquantel (Profender®, Bayer). Treatments were administered topically on Days 0 and 30, and efficacy was assessed by fecal EPG counts conducted on Days 14, 30, and 60. All cats completed the entire study. At enrollment, all cats were infected with Toxocara cati. Compared to pre-treatment, geometric mean T. cati EPG counts on Days 14, 30, and 60 were reduced by >99.9% in both treatment groups. There were no treatment-related adverse events in either study. Monthly topical administration of Revolution® Plus / Stronghold® Plus providing a minimum of 6 mg/kg selamectin and 1 mg/kg sarolaner was safe and effective in the prevention of heartworm disease and the treatment of roundworm infection in cats enrolled as veterinary patients in Japan.

Efficacy of a topical formulation of selamectin plus sarolaner against induced infestations of Amblyomma americanum on cats and prevention of Cytauxzoon felis transmission

Cytauxzoonosis, caused by infection with Cytauxzoon felis, is the most severe tick-borne disease of cats. The purpose of our study was to determine the efficacy of selamectin (6.0 mg/kg) plus sarolaner (1.0 mg/kg) formulated in combination (Revolution® Plus / Stronghold^® Plus, Zoetis) applied topically once a month on cats for three months against induced infestations of Amblyomma americanum adults and to evaluate the effectiveness of the product in preventing the transmission of C. felis. This study was conducted in two phases. Sixteen cats were dosed with selamectin/sarolaner or a placebo (vehicle control) on Days 0, 28, and 56. In phase 1, each cat was infested with 50 (±5) unfed adult A. americanum on Day 4 and tick counts were conducted on Day 6 (48 h post infestation) and Day 7 (72 h post infestation) to evaluate acaricidal efficacy. In phase 2, to confirm acaricidal efficacy and evaluate prevention of C. felis transmission, each cat was infested on Day 60 with 50 (±5) adult A. americanum acquisition fed as nymphs on two C. felis-infected donor cats. Tick counts were conducted on Day 62 (48 h post infestation) and Day 63 (72 h post infestation). Blood samples were collected on Days -9, 60, 70, 76, and 90 and tested for infection with C. felis. Placebo cats were adequately infested on all count days, with least squares (geometric) mean live tick counts ranging from 34.0 (28.8) to 46.1 (46.0). Treatment reduced the least squares (geometric) mean counts compared to placebo by 27.1 (32.1)% and 90.4 (96.8)% on Days 6 and 7, respectively. The corresponding percent reductions were 56.4 (60.6)% and 94.7 (97.3)% on Days 62 and 63, respectively. Least squares mean counts were significantly lower in the treated group compared with the placebo group on all count days (P ≤ 0.0286). All cats were negative for C. felis by PCR prior to study start. In phase 2, seven cats in the control group and no cats in the selamectin/sarolaner group became infected with C. felis (P = 0.0017). Topical treatment with selamectin/sarolaner was >90% effective in reducing A. americanum tick counts 72 h after infestation and prevented the transmission of C. felis from infected ticks following the third of three monthly treatments. Revolution^® Plus / Stronghold^® Plus offers an option for the control of A. americanum infestations on cats and for preventing the transmission of C. felis to cats.