Q&A: Inside the Innovations that Help NexGard® PLUS Fight Heartworm Disease and More

A man and woman play with a dog outside

With Labor Day in the rear-view mirror, it may seem like the risk of heartworm disease is behind us, too.  Yet as fall approaches, it’s important to not forget that heartworm disease protection is recommended year-round for dogs in the United States.

As noted on the heartworm disease preventive labels, and recommended by the American Heartworm Society, all dogs should be on heartworm disease prevention year-round. 

In this Q&A, Dr. Dean Dailey, DVM, U.S. technical lead for the NexGard® franchise at Boehringer Ingelheim Animal Health, takes us behind the scenes to share how NexGard® PLUS (afoxolaner, moxidectin and pyrantel chewable tablets) was designed using an optimized dose of moxidectin to provide protection against heartworm disease.

Q: Which parasites does NexGard PLUS protect dogs from?

Dr. Dailey: NexGard PLUS is a recently FDA-approved and new-to-market monthly beef-flavored soft chew that protects dogs from fleas, ticks, heartworm disease, roundworms and hookworms. By combining internal and external parasite protection in a tasty, beef-flavored soft chew, NexGard® PLUS helps make monthly compliance easy and enjoyable for pets and pet owners.

It’s important to remember that every dog should be protected from heartworm disease, and it is essential that the veterinary community focuses on increasing the number of dogs that receive heartworm disease prevention year-round. At Boehringer Ingelheim Animal Health, we strive to work with the veterinary community to find ways that we can help increase the number of dogs that are receiving this essential prevention.

Q: Does NexGard PLUS offer immediate protection against heartworm disease?

Dr. Dailey: The minimum dose of moxidectin used in NexGard PLUS — 12 micrograms per kilogram (mcg/kg) — is higher than the doses previously shown to be 100% effective against susceptible heartworm isolates from the first dose. 

Q: Does NexGard PLUS offer protection from rare, resistant heartworm isolates?

Dr. Dailey: All oral heartworm disease preventives currently on the market that contain moxidectin have been formulated in a way that is designed to enhance the efficacy against rare, resistant heartworm isolates. This is important because in the past two decades, several resistant isolates of Dirofilaria immitis have been identified in the United States. These resistant subpopulations appear to be rare, only seen in small parts of the country and do not appear to be widespread. That said, while they may be uncommon and not an issue in most of the country, enhancing the efficacy against less sus2011ceptible heartworms was a factor in determining the moxidectin dose to be used in NexGard PLUS.

A quick history lesson: The first moxidectin-containing oral heartworm disease preventive was approved in 1997 with a recommended minimum dose of 3 mcg/kg. In additional laboratory studies, single oral doses of moxidectin dosed as low as 0.5 mcg/kg have been shown to be 100% effective in preventing heartworm disease against susceptible isolates.1 Effectiveness against rare, less susceptible heartworm isolates can be improved by increasing the oral moxidectin mcg/kg dose and/or increasing the number of monthly administrations.

So, with the intent of enhancing efficacy against resistant isolates, the minimum dose of moxidectin used in NexGard PLUS is 12 mcg/kg and recommended to be given monthly year-round.

At this time, no laboratory studies have been conducted evaluating the efficacy of the NexGard PLUS product against a known resistant heartworm isolate.

Q: Why was NexGard PLUS studied over a six-month period?

Dr. Dailey: Because the dose of moxidectin used in NexGard PLUS was optimized to enhance the efficacy against rare, resistant heartworm isolates, a longer, more clinically relevant 6-month timeframe also factored into the study design used for product approval. 

The label for NexGard PLUS states: “For heartworm disease prevention, give once monthly for at least six months after last exposure to mosquitoes.” This label language reflects the intentional clinical study design for testing safety and efficacy of NexGard PLUS in conditions that closely represent the real-world treatment recommendations for year-round heartworm disease prevention.

All heartworm studies were conducted using six monthly doses after last exposure to mosquitoes or infection. In all three heartworm clinical studies — two laboratory studies and one multicenter field study — conducted with the product, NexGard PLUS was 100% effective in preventing heartworm disease.2 

Q: How does the optimized moxidectin dose balance efficacy and safety? 

Dr. Dailey: While taking steps to enhance the efficacy against resistant isolates helped guide decisions about the moxidectin dose used for NexGard PLUS, the safety profile of the product remained a priority.

In the safety studies conducted for NexGard PLUS, including the margin of safety study, the heartworm positive safety study, the field safety study, and the avermectin-sensitive collie safety study, the product was well tolerated. In fact, in the avermectin-sensitive collie safety study, no clinical signs of avermectin toxicity were noted in any dog at any time, even in MDR1-deficient Collies receiving one-, three- and five-times the maximum label dose. 


1 Freedom of Information Summary, PROHEART® Tablets, NADA 141-051, May 1997.

2 NexGard PLUS prescribing information: https://docs.boehringer-ingelheim.com/NexGard_PLUS_PI_2023.pdf

NexGard® PLUS Important Safety Information

NexGard® PLUS (afoxolaner, moxidectin, and pyrantel chewable tablets) are for use in dogs only. The most frequently reported adverse reactions reported in clinical trials were diarrhea, vomiting, lethargy, and itching. NexGard® PLUS contains afoxolaner, a member of the isoxazoline class, which has been associated with neurologic adverse reactions including tremors, ataxia, and seizures in dogs with or without a history of seizures. Use with caution in dogs with a history of seizures or neurologic disorders. The safe use of NexGard® PLUS has not been evaluated in breeding, pregnant, or lactating dogs. Dogs should be tested for existing heartworm infection prior to starting a heartworm disease preventive. For more information, click here for full prescribing information or visit NexGardPLUSClinic.com.

Boehringer Ingelheim Animal Health

Boehringer Ingelheim Animal Health is working on first-in-class innovation for the prediction, prevention, and treatment of diseases in animals. For veterinarians, pet owners, farmers, and governments in more than 150 countries, we offer a large and innovative portfolio of products and services to improve the health and well-being of companion animals and livestock. As a global leader in the animal health industry and as part of family-owned Boehringer Ingelheim, we take a long-term perspective. The lives of animals and humans are interconnected in deep and complex ways. We know that when animals are healthy, humans are healthier too. By using the synergies between our Animal Health and Human Pharma businesses and by delivering value through innovation, we enhance the health and well-being of both.

For more information visit www.boehringer-ingelheim.com/animal-health.

Boehringer Ingelheim

Boehringer Ingelheim is working on breakthrough therapies that transform lives, today and for generations to come. As a leading research-driven biopharmaceutical company, the company creates value through innovation in areas of high unmet medical need. Founded in 1885 and family-owned ever since, Boehringer Ingelheim takes a long-term perspective. More than 52,000 employees serve over 130 markets in the three business areas, Human Pharma, Animal Health, and Biopharmaceutical Contract Manufacturing. Learn more at www.boehringer-ingelheim.com.

Media Contact

Brett Israel
Boehringer Ingelheim Animal Health
Director of PR and Communications, U.S. Pets

NexGard® is a registered trademark of Boehringer Ingelheim Animal Health France, used under license. ©2023 Boehringer Ingelheim Animal Health USA Inc., Duluth, GA. All rights reserved. US-PET-0812-2023.