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The Side Effects of Heartgard Plus Worming Treatment

 by simone on 13 May 2014 |
5 Comment(s)

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The old adage that prevention is better than a cure is never more true, or more important, than with your pet and worm treatments. Roundworm, hookworm and heartworm are easily transferred via mosquitoes or faeces and therefore commonly affect our pets. If left untreated, worms can spread and grow, creating serious complications to your pet’s intestinal and respiratory systems. A worm infestation can lead to severe digestive problems, heart failure and even death for your pet. 

Worms can also be transferred to humans so it is essential that you have an effective worming care plan. Protection against infection needs to be carried out regularly. Luckily Heartgard Plus is a monthly, easy to administer, very safe and proven treatment for worm control. It prevents worms developing to the dangerous adult stage and is available for both dogs for cats. 

It’s highly likely that every puppy or dog has been exposed to worms. Puppies need to be wormed every two weeks until 12 weeks of age and lactating females should also be treated. Dogs over 12 weeks old require frequent treatment for the rest of their lives. 

Heartgard Plus is available in different dosages for animals of different weights. It comes as a chewable and deliciously tasty tablet (or so I’ve observed). The dosage is designed to be chewed, rather than swallowed whole so you can always break it up and add it to your pet’s food if needed. You’ll need to make sure your pet consumes the entire dose, so observe them during administration and for a short time afterwards.

It is very important that you talk to your vet before beginning any treatment for heartworm. Not just to verify the correct dosage, but there can be severe reactions, similar to toxic shock, in animals who already have heartworm infections and are then given heartworm medication. Your dog will need to be tested, and if infected, adult heartworms and larvae (microfilariae) treated before beginning any course of worm control.

If you’re currently enjoying a nice meal, it’s best you put your meal aside for now as we take a closer look at these ghastly, villainous little worms.

Roundworms (ascarids) are the most common worms affecting dogs and cats. 
Virtually every puppy is infected with roundworms at birth or become infected via their mother’s milk. 

Adult worms are found in the intestine and can grow 2-3mm wide and up to 20cm long. Roundworms cause diarrhoea and vomiting, weight loss, poor growth, a pot-bellied appearance and lethargy. If left untreated or in severe cases, pneumonia and obstruction of the intestine or digestive system can occur.

In infected animals, the adult worms lay eggs that are then expelled in faeces. Other animals become infected by ingesting contaminated soil or eating other infected animals such as mice, rodents or birds. The eggs then hatch in the animal’s stomach, feeding on content found here and develop into egg-laying adults. Roundworm larvae and adults can also be found in other organs such as the liver and lungs but generally remain in the digestive system. 

Hookworms are another intestinal parasite that most commonly affect young dogs and cats. The worms attach to the host animal's intestinal lining and feed on blood, tissue and fluid. As with roundworm, larvae and adult egg-laying worms live in the intestine. Some larvae attach to other organs and can be particularly problematic for your pet if they migrate through the respiratory system. 

Hookworm eggs are expelled in the animal’s faeces. Dogs and cats can be infected by ingesting contaminated soil or from larvae penetrating the skin. Puppies can also be infected through their mother’s milk.

Bloody diarrhoea is a common symptom of hookworm. Other signs of infection are intestinal upset, pale gums, weight loss, stunted growth and poor coat condition. Serious loss of blood and anaemia can result from large numbers of worms being present or in puppies. In extreme cases this can lead to death.

Heartworm is the deadliest of all parasites and although infection is more common in dogs, cats are also susceptible. The worms inhabit the animal's lungs, heart and pulmonary arteries and can cause heart failure or death. 
Puppies should begin heartworm prevention by at least 12 weeks of age. 

Primarily it is actually the lungs that are affected by heartworm but the heart, circulatory system and even liver and kidneys may also be damaged. The symptoms indicating heartworm infection include coughing, shortness of breath, respiratory sounds, fainting, lethargy, weight loss, blood present in the saliva or mucus, abdominal swelling, vomiting and loss of appetite.

Heartworms are transmitted by mosquitoes and when an infected mosquito bites another animal, the heatworm larvae (microfilariae) are transferred. These larvae migrate through tissue and the host animal's circulatory system to the lungs, heart and pulmonary arteries, feed on blood and grow to maturity, some worms can reach 30cm in length and 2cm in width. Heartworm larvae can survive in the bloodstream of a host animal for two years. 

Heartworms will lead to the inflammation of tissue, blood clotting and the thickening of blood vessel walls. The animal’s blood pressure rises and cardiac strain is increased. 

There are very serious side effects if a dog is treated with prevention medicine and is already infected with heartworm.

Side Effects
As with any medication, there is the potential for unpleasant side effects and the possibility of individual sensitivities for some pets. However, tests show that Heartgard Plus is safe and well tolerated when used correctly, having a very low incidence of digestive and neurological side effects. 

Heartgard Plus uses ivermectin which causes paralysis and death to the parasitic worms. The dosage of ivermectin contained in Heartgard is relatively low, with little risk of side effects. As mentioned, it is vital that you do not start a worming program prior to having your pet checked for the presence of heartworm. 

Check the dosage required for your pet as serious side effects often result from a larger dose being administered than recommended. If the dosage given is correct and you notice any of the side effects listed below take your pet to the vet immediately.

  • Digestive Problems. The most common side effect associated with Heartgard Plus is digestive problems such as nausea, vomiting and diarrhoea. In clinical field trials, vomiting or diarrhoea within 24 hours of dosing was observed in only 1.1% of cases.
  • Hypersalivation
  • Depression and Lethargy. Depression, lethargy, lack of appetite and loss of interest in activities has been noticed in some pets.
  • Lack of Coordination (Ataxia), Disorientation and Hind Leg Paralysis
  • Stumbling, running into walls and furniture or paralysis could occur.
  • Dilated Pupils (Mydriasis) or Blindness
  • Crying, Agitation
  • Low Body Temperature and Hypothermia
  • Seizures and Muscle Tremors. Seizures, tremors and convulsions are very rare and may mean your pet has a particular sensitivity, the dosage is too high or that heartworm was already present. 

Susceptible Breeds
Some dog breeds have a mutation in the multi-drug resistance gene (MDR1) making them more sensitive to ivermectin at very elevated dose levels (16 times more than the recommended level). In trials, no adverse reactions were observed in dogs at ten times the Heartgard recommended dose.

This gene mutation is known to occur most commonly in breeds such as Collies, Australian Shepherds, Shelties and Long-haired Whippets. The level of ivermectin used for heartworm prevention is generally safe and at a low level suitable for these dogs. You can talk to your vet about testing your dog for the gene mutation.

When dosage and treatment instructions are followed, Heartgard Plus is a safe and effective worming care plan. It is approved for animals as young as 6 weeks and pregnant or lactating cats and dogs. Administering the medication is as simple as giving your pet a chewable treat each month. The packaging also has a calendar so you will never lose track of where you are up to. Peace of mind has never been so easy. 


Melody - Comment
Melody20 Jan 2018Reply
Our dog was positive on his heartworm test but they gave him prednisone an muscle relaxers plus heartguard....we thought he was dying lastnight because all he did was lay there eyes were dialated and he would cough and had this mucous and foam type drooling....we thought he would die during night for sure but today he is getting up some an nodrool.....happening.....he reallying scared us???????????????
Sheree' Welch - Comment
Sheree' Welch03 Apr 2018Reply
My dog Molly was treated for heartworms in July last year & was heartworm free at her 6 month check up. As suggested, I've continued to give her heartguard monthly. However, for the past 2 minths, I've noticed her coughing the day after it's given & the cough lasts a day or two. Suggestions?
Shirley - Comment
Shirley21 Apr 2018Reply
Might gave my 8 year old dog heartguard plus this morning. Tonight her back legs are not working. Is there anything I can do for her right now and will this pass
Natalie Wood - Comment
Natalie Wood13 Sep 2018Reply
My dogs hind legs are having problems too. How are yalls dogs now?
Jody Creighton  - Comment
Jody Creighton 28 Oct 2018Reply
I gave my Lab/Basset her Heartguard dose Sunday and since the following Tuesday her back left leg has hurt her. I’ve been researching hip dysphasia symptoms and joint pain in senior dogs but thought I’d check to see if MAYBE any other dogs had leg pain after their heart worm meds and found this thread. Did your dogs leg issues clear up?

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