Efficacy of oral afoxolaner plus milbemycin oxime chewables against induced infestations with Dermacentor reticulatus in dogs

Efficacy of an oral combination of afoxolaner and milbemycin oxime for the prevention of transmission of Babesia canis by Dermacentor reticulatus ticks to dogs

BACKGROUND

Canine babesiosis is a tick-borne disease of significant veterinary importance in dogs. It is caused by Babesia canis in Europe, where it is transmitted by Dermacentor reticulatus ticks.

METHODS

A blinded, randomized, good clinical practice (GCP) and negative control experimental study was conducted to verify the efficacy of NexGard Spectra® in reducing the transmission of B. canis by D. reticulatus to dogs. NexGard Spectra® (IVP) is an oral product for dogs combining afoxolaner, an acaricide/insecticide compound from the isoxazoline class, and milbemycin oxime, a nematicide compound from the macrocyclic lactone class. Three groups of eight dogs were used; one group orally treated on day 0 with the IVP at the minimum recommended dose and two untreated control groups. On day 1, dogs from the treated group and from control group 1 were infested with 50 D. reticulatus adult ticks of 50/50 sex ratio infected with B. canis at a 23% infection rate. On day 28, dogs from the treated group and from control group 2 were infested similarly to those on day 1. Ticks were removed 6 days after each infestation.

RESULTS

Seven to nine days after each infestation, all untreated control dogs displayed clinical signs of canine babesiosis, i.e., lethargy, and/or dark urine, and/or > 39.5 °C rectal temperature. Blood was collected for microscopical blood smear examination, and for polymerase chain reaction (PCR) analysis. The blood smears from all untreated control dogs were positive for Babesia and all the PCR analyses were positive for B. canis. The control dogs were rescue treated. All control dogs were confirmed positive for B. canis by IFA on day 21 (control group 1) and on day 42 (control group 2). None of the IVP-treated dogs expressed any clinical sign of canine babesiosis following each of the two infestations of days 1 and 28 and until day 56. Blood was collected for IFA and PCR analyses from the treated dogs on days 21, 28, 42, and 56, and all results were negative.

CONCLUSIONS

In this study, the antiparasitic treatment prevented the transmission of B. canis to dogs following induced infestations.

Treatment of canine sarcoptic mange with afoxolaner (NexGard®) and afoxolaner plus milbemycin oxime (NexGard Spectra®) chewable tablets: efficacy under field conditions in Portugal and Germany

The efficacy of NexGard^® and NexGard Spectra^® against sarcoptic mange in dogs was evaluated in a clinical field study. Skin scrapings from dogs presenting signs suggestive of sarcoptic mange were examined to confirm infestation. A total of 106 dogs were screened at eight sites in Portugal and Germany. In all, 80 dogs that had demonstrated ≥5 live Sarcoptes mites in five skin scrapings were enrolled, scored for specific clinical signs (pruritus; papules and crusts; alopecia), and allocated at random to receive either NexGard^® or NexGard Spectra^® twice, one month apart per label instructions. To determine efficacy, live Sarcoptes mites in five skin scrapings per dog were counted, and clinical signs were scored one month and two months after first treatment and compared to pre-treatment (baseline) values. Based on compliance, 65 dogs were determined to be evaluable cases at the end of the study. The efficacy, in terms of reduction of geometric mean live Sarcoptes mite counts, was 98.9% and 99.7% for NexGard^®-treated (n = 38) and 99.6% and 100% for NexGard Spectra^®-treated dogs (n = 27) at one month and two months after treatment initiation (p < 0.001, both treatments). Both treatments resulted in a significant improvement in pruritus, papules and crusts, and alopecia one month and two months after treatment initiation (p = 0.0001, both treatments). In conclusion, this field study confirms that both NexGard^® and NexGard Spectra^® administered twice one month apart provide an effective and safe treatment against sarcoptic mange in dogs.

Efficacy against nematode infections and safety of afoxolaner plus milbemycin oxime chewable tablets in domestic dogs under field conditions in Europe

Afoxolaner (AFX) plus milbemycin oxime (MO) combination chewable tablets (NexGard Spectra®, Merial) were evaluated for safety and efficacy against naturally acquired nematode infections in domestic dogs in a multi-centre, positive control, blinded field study using a randomized block design based on the order of presentation for allocation. In total, 408 dogs confirmed positive for naturally acquired infections of intestinal nematodes by pre-treatment faecal examination were studied in ten countries in Europe (Albania, Austria, Bulgaria, France, Germany, Hungary, Italy, Lithuania, Romania and Slovakia). Pre-treatment faecal examination revealed Toxocara, Toxascaris, hookworm, Trichuris and/or Capillaria nematode infections in 134, 30, 223, 155 and 14 dogs, respectively. Dogs were allocated to one of two treatment groups in a ratio of 1, AFX + MO chewables (≥2.5 mg AFX + ≥0.5 mg MO per kg body weight, according to dose bands; 207 dogs), and 1, MO plus praziquantel (PRZ) chewables (Milbemax®, Novartis; ≥0.5 mg MO + ≥5 mg PRZ per kg body weight, according to the manufacturer's instructions; 201 dogs) and treated once. For evaluation of efficacy based on reduction of faecal nematode egg counts, two faecal samples, one collected prior to treatment and one collected 9 to 21 days after treatment, were examined using modified McMaster techniques. For evaluation of systemic safety, dogs were examined by a veterinarian before treatment administration and at study end, and dog owners observed the health status of their dogs until the end of the study and reported any abnormal observation. For dogs treated with AFX + MO chewables, the efficacy was 99.7, 99.7, 97.2, 99.7 and 99.7 % for Toxocara, Toxascaris, hookworm, Trichuris and Capillaria, respectively; and the efficacy was 99.5, 99.4, 94.3, 99.9 and 98.0 %, respectively, for the MO + PRZ-treated dogs (p ≤ 0.002 for all nematodes and both treatments). For Toxocara, hookworm and Trichuris, non-inferiority analysis demonstrated that the efficacy of AFX + MO chewable tablets was equal to or better than that of MO + PRZ. In spite that both treatments were ≥98 % efficacious against Toxascaris and Capillaria, a hypothesis of non-inferiority for both genera could not be established due to the low number of dogs infected with these parasites. No treatment-related adverse experiences were observed throughout the study. For both treatments, all dogs were given a systemic safety score of 'excellent' apart from one dog in each treatment group which received a score of 'acceptable'. AFX + MO combination chewables were shown to be safe and demonstrated a high level of efficacy when administered once to dogs infected with a broad range of parasitic nematodes under field conditions.

The intravenous and oral pharmacokinetics of afoxolaner and milbemycin oxime when used as a combination chewable parasiticide for dogs

The pharmacokinetics of afoxolaner and milbemycin oxime (A3 and A4 forms) in dogs were evaluated following the oral administration of NexGard Spectra^® (Merial), a fixed combination chewable formulation of these two active pharmaceutical ingredients. Absorption of actives was rapid at levels that provide the minimum effective doses of 2.5 mg/kg and 0.5 mg/kg of afoxolaner and milbemycin oxime, respectively. The time to maximum afoxolaner plasma concentrations (t_max ) was 2-4 h. The milbemycin t_max was 1-2 h. The terminal plasma half-life (t_1/2 ) and the oral bioavailability were 14 ± 3 days and 88.3% for afoxolaner, 1.6 ± 0.4 days and 80.5% for milbemycin oxime A3 and 3.3 ± 1.4 days and 65.1% for milbemycin oxime A4. The volume of distribution (V_d ) and systemic clearance (Cls) were determined following an IV dose of afoxolaner or milbemycin oxime. The V_d was 2.6 ± 0.6, 2.7 ± 0.4 and 2.6 ± 0.6 L/kg for afoxolaner, milbemycin oxime A3 and milbemycin oxime A4, respectively. The Cls was 5.0 ± 1.2, 75 ± 22 and 41 ± 12 mL/h/kg for afoxolaner, milbemycin oxime A3 and milbemycin oxime A4, respectively. The pharmacokinetic profile for the combination of afoxolaner and milbemycin oxime supports the rapid onset and a sustained efficacy for afoxolaner against ectoparasites and the known endoparasitic activity of milbemycin oxime.

Monthly administrations of milbemycin oxime plus afoxolaner chewable tablets to prevent Angiostrongylus vasorum infection in dogs

Background

Infection of dogs with the cardiopulmonary nematode Angiostrongylus vasorum may result in severe clinical disease therefore adequate prevention is necessary. A randomized, negative control, blinded study was conducted to evaluate the efficacy in the prevention of canine A. vasorum infection after monthly administrations of NexGard Spectra®, a novel chewable tablet formulation combining the insecticide and acaricide afoxolaner and the anthelmintic milbemycin oxime, in a multiple challenge (trickle infection) model.

Methods

Twenty beagle dogs were challenged orally with doses of approximately 32–43 third-stage larvae of A. vasorum once every other week on seven occasions (Study Days -7, 7, 21, 35, 49, 63 and 77). Ten dogs were administered NexGard Spectra® as close as possible to the minimum recommended dose of afoxolaner and milbemycin oxime, i.e. 2.5 mg/kg body weight and 0.5 mg/kg body weight, respectively, four times at monthly intervals (Study Days 0, 28, 56 and 84) while the remaining ten dogs served as untreated controls. For parasite recovery and count, dogs were euthanized humanely and necropsied six to eight days following the last treatment (Study Days 90–92). Beginning six weeks after first inoculation, faeces were collected on a bi-weekly basis and examined for first-stage larvae of A. vasorum.

Results

Untreated dogs harboured 39–95 adult A. vasorum (geometric mean, 66.4), while zero to 24 adult A. vasorum were recovered from the treated dogs (geometric mean, 3.4; P < 0.0001). Thus, efficacy of NexGard Spectra® administered at monthly intervals against incoming A. vasorum was 94.9 %. Compared to the untreated controls, larval excretion of the treated dogs was reduced by 99.9 % (P < 0.0001).

Conclusion

Results of this study demonstrate that NexGard Spectra®, when administered at monthly intervals, can effectively prevent canine A. vasorum infection.

Efficacy of oral afoxolaner plus milbemycin oxime chewables against induced gastrointestinal nematode infections in dogs

The efficacy of oral afoxolaner plus milbemycin oxime combination chewables against induced gastrointestinal nematode infections in dogs was evaluated in six separate studies. Two studies were performed to evaluate the efficacy of the product against Toxocara canis, two studies evaluated the efficacy against Toxascaris leonina, one study evaluated the efficacy against Ancylostoma braziliense, and one study evaluated the efficacy against Ancylostoma caninum. In the A. caninum study, the efficacy of milbemycin oxime alone and afoxolaner alone was also evaluated. Dogs in all studies were inoculated with infective eggs or larvae and confirmed to have patent infections based on a fecal examination prior to allocation to study group and treatment. Each study utilized a randomized block design with blocks based on pre-treatment body weight. All dogs were assigned to blocks based on body weight, and then each dog within a block was randomly assigned to treatment group. There were two groups of 10 dogs each in the T. canis, T. leonina, and A. braziliense studies: 1) an untreated (control) group and 2) a group treated with afoxolaner plus milbemycin oxime chewables (NexGard Spectra(®), Merial). This group was treated at a dose as close as possible to the minimum effective dose of afoxolaner and milbemycin oxime (2.5mg+0.5mg per kg body weight, respectively) once on Day 0 using whole chews. There were four groups of 10 dogs each in the A. caninum study: 1) untreated (control), 2) NexGard Spectra(®) as described above, 3) milbemycin oxime alone (dose of at least 0.5mg per kg of body weight) and 4) afoxalaner alone (dose of at least 2.5mg per kg body weight). For parasite recovery and counts, dogs were euthanized humanely and necropsied seven days after treatment. The efficacy of the afoxolaner plus milbemycin oxime combination was ≥98% against T. canis, ≥95.8% against T. leonina, and 90.2% against A. braziliense. Efficacy of the combination against A. caninum was 99.7%, while the efficacy of milbemycin oxime alone was 99.6% and the efficacy of afoxolaner alone was 2.1%. Dogs treated with afoxolaner plus milbemycin oxime chewables had significantly (p≤0.0002) fewer nematodes than the untreated controls in all studies. There were no adverse events or other health problems that were related to treatment with Nexgard Spectra(®) in these studies. The results of these controlled studies demonstrate the high efficacy of the afoxolaner plus milbemycin oxime chewables against a broad range of canine intestinal nematode infections.

Dermacentor reticulatus: a vector on the rise

Dermacentor reticulatus is a hard tick species with extraordinary biological features. It has a high reproduction rate, a rapid developmental cycle, and is also able to overcome years of unfavourable conditions. Dermacentor reticulatus can survive under water for several months and is cold-hardy even compared to other tick species. It has a wide host range: over 60 different wild and domesticated hosts are known for the three active developmental stages. Its high adaptiveness gives an edge to this tick species as shown by new data on the emergence and establishment of D. reticulatus populations throughout Europe. The tick has been the research focus of a growing number of scientists, physicians and veterinarians. Within the Web of Science database, more than a fifth of the over 700 items published on this species between 1897 and 2015 appeared in the last three years (2013–2015). Here we attempt to synthesize current knowledge on the systematics, ecology, geographical distribution and recent spread of the species and to highlight the great spectrum of possible veterinary and public health threats it poses. Canine babesiosis caused by Babesia canis is a severe leading canine vector-borne disease in many endemic areas. Although less frequently than Ixodes ricinus, D. reticulatus adults bite humans and transmit several Rickettsia spp., Omsk haemorrhagic fever virus or Tick-borne encephalitis virus. We have not solely collected and reviewed the latest and fundamental scientific papers available in primary databases but also widened our scope to books, theses, conference papers and specialists colleagues’ experience where needed. Besides the dominant literature available in English, we also tried to access scientific literature in German, Russian and eastern European languages as well. We hope to inspire future research projects that are necessary to understand the basic life-cycle and ecology of this vector in order to understand and prevent disease threats. We conclude that although great strides have been made in our knowledge of the eco-epidemiology of this species, several gaps still need to be filled with basic research, targeting possible reservoir and vector roles and the key factors resulting in the observed geographical spread of D. reticulatus.

Efficacy of afoxolaner plus milbemycin oxime chewable tablets against naturally acquired intestinal nematodes in dogs

The efficacy of oral afoxolaner plus milbemycin oxime combination chewable tablets (NexGard Spectra, Merial) against naturally acquired intestinal nematode infections in dogs was evaluated in six negative control, blinded studies including a total of 114 dogs. Dogs were selected based on a pre-treatment fecal examination indicating patent infections with hookworms (two studies), Toxocara or Toxascaris ascarids (one study each) or Trichuris whipworms (two studies). In each study, dogs were assigned to blocks of two animals each, based on decreasing pre-treatment body weight and were randomly allocated to one of two groups consisting of eight, nine or 10 dogs: untreated (control) or treated with the combination chewable tablet formulation. Chewable tablets were combined to provide doses of actives as close as possible to the minimum effective dose of afoxolaner and milbemycin oxime, i.e., 2.5 mg/kg body weight and 0.5 mg/kg body weight, respectively, once on Day 0. For parasite recovery and count, dogs were euthanized humanely and necropsied seven or eight days after treatment. A single treatment with afoxolaner plus milbemycin oxime chewable tablets provided 94.8% and 90.9% efficacy against adult Ancylostoma braziliense and A. caninum, respectively, 97.8% and 99.4% efficacy against adult Toxocara canis and Toxascaris leonina, respectively, and ≥98.3% efficacy against adult Trichuris vulpis. Compared to untreated controls, nematode counts of the treated dogs were significantly reduced (F-test; p<0.002). In addition, analysis of the pooled data across studies revealed that treatment with afoxolaner plus milbemycin oxime chewable tablets reduced adult Uncinaria stenocephala burdens by 74.9% (p=0.002). All dogs tolerated the treatment well based on clinical observations post-treatment and daily clinical observations. No adverse experiences or other clinical problems related to the treatment were observed throughout the studies. The results of this series of controlled studies demonstrated high efficacy and excellent acceptability and safety of the afoxolaner plus milbemycin oxime chewable tablets when administered for treatment of a broad range of canine intestinal nematode infections.