Thank you for your question. I would not expect the lethargy or diarrhea to last more than 12-24 hours.
Nexgard® Possible Side Effects
Lethargy. Diarrhea. Loss of appetite. Allergic reactions: hives or facial swelling.
It has minimal side effects, and has been shown to be safe at up to 5 times the recommended dose. In a 90-day field study, 415 dogs were administered afoxolaner and no serious adverse reactions were observed with NexGard. The most frequent adverse reaction was vomiting, with 17 dogs experiencing that reaction.
Your veterinarian may decide to wait before a costly test is conducted; once your dog stops taking the tablets, the signs may resolve. It is important to understand that this may take some time, as this flea and tick treatment is given once a month, and it may still be in their system for up to 30 days.
As with any oral medication, vomiting, diarrhea, allergic or neurological reactions can occur. While we take all adverse reactions very seriously, our doctors have actually seen less reactions with oral Nexgard than with other topical flea and tick prevention options.
If a dog vomits within 2 hours of administration of a Nexgard tablet, a new tablet should be given. If vomiting occurs after 2 hours, re-dosing is not necessary. There are no known drug interactions with afoxolaner.
Usually, NexGard starts killing fleas within 8 hours of exposure and ticks within 48 hours of exposure. We should note that if there is a heavy flea infestation in the house, you will keep seeing fleas on the dog for a couple of days after using NexGard.
As NexGard is an oral treatment, there are no restrictions on swimming, bathing and shampooing before or after administration.
These products are safe to use in the majority of pets, but there are some pets that cannot tolerate the medication (specific liver disorders, pre-existing seizure disorders).
In the US field study, one dog with a history of seizures experienced a seizure on the same day after receiving the first dose and on the same day after receiving the second dose of NexGard. This dog experienced a third seizure one week after receiving the third dose.
“NexGard (afoxolaner) is one of the isoxazoline class of parasiticides. Please do NOT use any of them again. There are now two isoxazoline-related class-action lawsuits in North America — one in Quebec and the other in New Jersey. The FDA finally has required warnings on the labels and product inserts.
NexGard® Recalls & Controversies
Although there have not been any FDA recalls for NexGuard®, the FDA has put out an alert for pet owners and veterinarians.
Adverse reactions such as excessive drooling, paw flicking/scratching, and ear twitching are often mild and can go away on their own. Although drooling may recur for several days after use of a flea-control product on an animal, most mild to severe clinical signs resolve within three days.
Seizures have been reported in dogs receiving isoxazoline class drugs, even in dogs without a history of seizures. Therefore, use with caution in dogs with a history of seizures or neurologic disorders. The safe use of NexGard in breeding, pregnant or lactating dogs has not been evaluated.”
If you give your dog or cat the flea and tick preventatives Bravecto, Nexgard, Simparica, or Credelio, the FDA wants you to be aware that these medications may cause neurological issues like stumbling, seizures, and twitching in your pet.
Both products are safe for dogs when following directions and have been approved by the FDA to treat and prevent flea and tick infestations. While Simparica was trialed and not approved, Nexgard has not yet been evaluated for use in breeding, pregnant, or lactating dogs.
NexGard® (afoxolaner) is for use in dogs only. The most frequently reported adverse reactions include vomiting, itching, lethargy, diarrhoea, and lack of appetite.
Simparica is an excellent choice for flea and tick protection. The monthly chew also comes with an option for heartworm protection, too, as Simparica Trio. But while Simparica is usually safe flea and tick treatment for dogs, it shouldn't be prescribed to dogs with a history of seizures.
NEXGARD SPECTRA should be administered at monthly intervals beginning within 1 month of the dog's first exposure to mosquitoes and continuing for 6 months after the dog's last exposure to mosquitoes (see EFFICACY).
Chewables Administered
60.1 to 121.0 lbs. Over 121.0 lbs. NexGard can be administered with or without food. Care should be taken that the dog consumes the complete dose, and treated animals should be observed for a few minutes to ensure that part of the dose is not lost or refused.
The most common reason is that the fleas are being killed and the dog is no longer being bitten by them. This can cause the dog to feel itchy and uncomfortable, which may lead to restlessness. Additionally, the chemicals in some flea treatments can be irritating to dogs, leading to discomfort and restlessness.
Vomiting, lethargy and diarrhea are the most common side effects reported. Seizures are quite high on both lists, with 22 each for both Nexgard and Bravecto for the first quarter of 2016. Nine deaths are reported for each drug for the same period. For Nexgard, five of the nine deaths were by euthanasia.
Nexgard can kill 99% of all infections in a single treatment. The product kills eggs, larvae, and full-grown parasites making it highly effective in protecting your dog's health.
Oral products, like Nexgard (Boehringer Ingelheim) and Bravecto (Merck Animal Health), contain isoxazoline derivatives that negatively affect the tick's nervous system, resulting in death of the tick. Oral products are effective and convenient.