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You generally don't expect deworming side effects in dogs to happen, but as with any medications they occasionally pop up. 

Generally, the side effects of dewormers in dogs are self-limiting, meaning that they don't have any major impact on the dog's health, leading to only some transient problems.

 However, this doesn't make the issue less concerning, countless dog owners are concerned about the side effects of canine dewormers and may be wondering what to do about them.

A Heavy Worm Burden

If your dog gets sick after you give him a dewormer, consider that in some cases, this may happen if your dog has a heavy worm burden. Affected dogs may get a nasty case of gastro-enteritis with diarrhea which sometimes has blood in it, explains veterinarian Dr. Sarah Snow.

In puppies, in particular, giving a dewormer when they have a heavy worm burden can lead to several issues. 

The heavy infestation of worms may cause an impaction as they're killed and pushed down the intestinal tract. 

For instance, some puppies with a heavy parasite loads can vomit after a worming as the parasites die. Usually, this is not a major concern as long as the puppy vomits just once or twice and remains over all bright, alert and playful, explains veterinarian Dr. Kara. 

When the worms are then on their way out through the intestines, the can still wreck some havoc too. A lot of inflammation may set in, which can lead to diarrhea, explains veterinarian Doc James.

In severe cases, when the dog's intestinal tract becomes blocked with dead worms, surgery may be needed. Signs that suggest a blockage include persistent vomiting and abdominal pain. 

On top of that, if the affected pup is straining from the worms, and the pup has a heavy burden, consider that this may lead to rectal prolapse. Rectal prolapse in puppies may show as the rectum sticking out.

If your dog has a heavy worm burden, he may require numerous dewormings. Consult with your vet about this. You may need to send a stool sample some time after deworming your dog the first time to check for the signs of the presence of any worms.

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Heavy worm infestations may cause dogs to develop inflammation and accompanying diarrhea after being dewormed. 

Heavy worm infestations may cause dogs to develop inflammation and accompanying diarrhea after being dewormed. 

Deworming Side Effects in Dogs

As mentioned, side effects from dewormers in dogs are usually self-limiting and short-lived. Affected dogs may therefore develop mild diarrhea and vomiting with a temporary loss of appetite. 

Usually, these cases resolve within a few days when the dog is provided with supportive care such as a bland diet consisting of boiled white rice and boneless, skinless chicken, points out Critical Care Vet, an Emergency and Critical Care Specialist.

You may also notice live or dead worms in your dog's stool. This happens because some types of dewormers causes the worms to become paralyzed, and therefore, they lose their grip on the gut wall.

In rare cases, a dog may develop an allergic reaction to the deworming drug. Symptoms of an allergic reaction includes signs of shock which include pale gums, trouble breathing, seizures and collapse. See your vet immediately if you notice any of these signs.

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“The only difference between a medicine and a poison is the dose." 

Dog Dewormer Overdose Symptoms

"Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy." These are the wise words from Paracelsus, who is credited as the father of modern toxicology.

Any dewormer, given in an overdose, has the potential to cause toxic effects. However, it may be quite difficult to overdose on some dewormers considering their wide safety margins with minimal side effects.

For instance, consider that Panacur, (generic name fenbendazole) an oral dewormer used to treat hookworm, roundworm, tapeworm, and whipworm infestations has been reported to be well tolerated, even at six times the recommended dose and three times its recommended duration (Source: Small Animal Toxicology, Third Edition, 2013). 

If you suspect you overdosed your dog or puppy and less than 2 hours have passed, consult with your vet. Chances are your dog didn't really receive a significant overdose, and if he did, you are on time to induce vomiting with your vet's assistance. You can induce vomiting in dogs at home by using 3 percent hydrogen peroxide.

Generally, symptoms of an overdose of dewormer in dogs include vomiting, loss of appetite and diarrhea. If you suspect that you overdosed your dog, consult with your vet immediately within business hours, or if after hours, consult with your 24 hours emergency vet or call the Pet Poison Helpline at 855-764-7661 a $59 dollar fee applies per consultation.

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