Comfortis Killed My Dog

No pet parent wants to deal with fleas because they are such dreadful bugs. They make a dog itchy, uncomfortable, and restless. Your vet recommended Comfortis as a safe flea preventative that works quickly on both dogs and pups. Unfortunately, it didn’t work as intended as you are now blaming it for the death of your dog. I can empathize with you and I am sorry for your loss.

This article will help you understand more about Comfortis, its safety, efficacy, side effects, alternatives, and much more.

What is Comfortis®?

They are chewable, beef-flavored tablets that you can give to your dog or cat to get rid of fleas and stop infestations for a month. Comfortis chewable tablets can be administered to dogs 14 years of age or older weighing 5.0 pounds or more.

How Does Comfortis Work?

When a dog consumes a Comfortis tablet, the medication begins to work immediately to treat fleas; within 30 minutes, adult fleas that are currently residing on the dog are killed. Comfortis can also be used to maintain dogs flea-free; even after ingestion, the medication keeps dogs flea-free.

Spinosad, the active component, affects the neurological system of the flea and kills all adult fleas. In the weeks following a treatment, fleas may return to your pet. Flea eggs laid prior to the treatment will produce these fleas. Comfortis has a 30-day expiration date, so gradually it will start working and eliminate both the old and new fleas. As a preventative measure, Comfortis will get rid of adult fleas on dogs before they can reproduce.


Comfortis killed all adult fleas within 30 minutes in a controlled research on Beagle dogs, and after 4 hours of ingestion, it completely eradicated all fleas. Further research revealed that this drug reduced the number of eggs produced by reinfested canines by approximately 99%.

Comfortis Killed My Dog

Here are some of the reasons why a dog can die after taking Comfortis:

Allergic reaction

Comforti’s active ingredient, spinosad, may be allergic to some dogs. This allergy can result in severe allergic symptoms like hives, itching, and even anaphylaxis. In extreme circumstances, this may be fatal.


Comfortis is a potent drug that must be taken exactly as prescribed by your veterinarian. Inadvertently giving a dog too much Comfortis might result in toxicity and other effects that could be lethal.

Pre-existing health conditions

Dogs who already have conditions like liver or kidney disease may be more vulnerable to Comfortis’ adverse reactions.

Drug interactions

If a dog is taking other medications, there may be drug interactions between Comfortis and those drugs that could result in adverse side effects or even death. Always inform your veterinarian about any drugs your dog is taking to prevent drug interactions.

Problems with quality control 

In a few rare instances, Comfortis quality control problems have been reported, resulting in some tablets having a higher concentration of the active component. This may result in an overdose and death.

The FDA has approved Comfortis for use in dogs and concluded that it is safe for the majority of animals. However, there is always a chance of unpleasant side effects or complications, just like with any medication.

When to Give Comfortis?

Preventative flea control is simpler than post-infestation control. Dogs should be given Comfortis before flea season to prevent an increase in fleas on them and eventually in your home. Giving the medication to dogs a month before the flea season begins will help stop fleas before they even become a problem. It can make the most sense to use Comfortis all year round if you reside in a warm climate. Comfortis is frequently administered along with another medication, such as Sentinel, to kill fleas in their pre-adult life stages (egg, larva, and pupa). Together, they create a more thorough defense.

Comfortis is only available with a prescription, and you should always follow your veterinarian’s recommendations when administering medication to your dog. The chewable pill should be given to dogs along with food. It tastes like beef to them and most of them will take it as a treat.

What Are The Side Effects Of Comfortis For Dogs?

The following are possible negative effects of Comfortis for dogs:


After taking Comfortis, some dogs may vomit. Normally, this is moderate and brief, but it can occasionally be severe and persistent. It’s crucial to call your vet if your dog vomits an hour after taking Comfortis.


Another possible Comfortis side effect is diarrhea. This might be brought on by the medication’s impact on the intestinal flora of the dog. It is crucial to call your veterinarian if your dog has diarrhea.


After taking Comfortis, some dogs may become lethargic. Normally, this is moderate and transient, but it can occasionally be severe and persistent. It’s crucial to call your veterinarian if your dog exhibits prolonged signs of lethargy.


Dogs taking Comfortis may get seizures. This severe adverse effect calls for quick veterinary care.

Decrease of Appetite

After taking Comfortis, some dogs might experience a decrease in appetite. Normally, this is moderate and transient, but it can occasionally be severe and persistent. It is crucial to call your veterinarian if your dog’s appetite does not improve within a few days.


After taking Comfortis, some dogs may develop itching. Normally, this is moderate and transient, but it can occasionally be severe and persistent. It is crucial to call your veterinarian if your dog is scratching excessively.

 The advantages of taking Comfortis to manage fleas and ticks outweigh the potential hazards, and these side effects are relatively uncommon. Nevertheless, it’s crucial to be aware of these possible side effects and to get in touch with your veterinarian if any appear.


Comfortis comes in 5 strengths and doses ranging from 14 mg to 28 mg per pound for weight categories from 5 lbs to 120 lbs. Only dogs over 3.5 months old and 5 pounds in weight are permitted to use this medicine.

Dosage ranges according to weight group:

  • 5 to 10 lbs: 140 mg
  • 10 to 20 lbs: 270 mg
  • 20 to 40 lbs: 560 mg
  • 40 to 60 lbs: 810 mg
  • 60 to 120 lbs: 1,620 mg


Pregnant dogs who receive large dosages of Comfortis are at an increased risk for early and late-term miscarriage as well as neonatal death. Additionally, researchers found that puppies born to dogs treated with Comfortis had low birth weights, difficulty controlling their body temperatures, and low activity levels.

Comfortis can be dangerous to nursing puppies since it travels through the mother’s milk. Consult your veterinarian for safe flea prevention choices for nursing dogs.

According to studies, taking Comfortis along with the dewormer ivermectin, which is used to treat mange, increases the risk of hepatotoxicity. According to research, using these two anti-parasitics simultaneously can result in impaired motor coordination, disorientation, seizures, and vision loss.

In dogs with epilepsy, this drug may cause seizures. At the beginning of the course of medication, keep a watchful eye on your dog, and if any pre-epileptic symptoms appear, schedule an appointment with the veterinarian.

Drug interactions

One of the few contraindications to Comfortis is the anti-parasitic drug ivermectin. Use of this medication in conjunction with other medications containing spinosad should be avoided as it may result in an overdose. Other drugs that should be avoided include;

  • Ivermectin
  • Trifexis
  • Topical and oral medications containing spinosad

Allergic reactions and sensitivity

Dogs with pork allergies or those taking drugs like Trifexis which contain spinosad shouldn’t be given Comfortis. The majority of dogs tolerate Comfortis well, and negative side effects are rare. Vomiting is the most typical adverse effect of spinosad sensitivity. Nausea usually goes away within a few hours, so there is usually no cause for alarm.

If your dog exhibits any of the following signs, whether or not they accompany nausea contact your vet:

  • Scratching
  • Confusion
  • Swelling of the face, mouth, throat, tongue, or extremities
  • Loss of consciousness
  • Seizures
  • Struggling to breathe

What If My Dog Throws Up After Taking Comfortis?

If your dog vomits after receiving Comfortis, it’s important to note the timing of the vomiting in relation to when the medication was administered. If the vomiting happens within a few minutes to an hour after administering the medication, the dog has likely had an adverse reaction to the medication. In this case, it’s advised to contact your veterinarian right away.

Examine further potential reasons for vomiting in dogs, such as food problems, infections, or underlying medical diseases. Consult your veterinarian to rule out any other potential causes if your dog has a history of vomiting or exhibits further symptoms including diarrhea, lethargy, or loss of appetite.

Does Seeing Fleas On My Dog Or Cat Mean The Treatment Isn’t Working? 

According to the label instructions, Comfortis kills fleas before they can lay eggs when applied monthly. Within a month of giving your pet Comfortis, if you notice fleas on your dog or cat, they are almost certain new fleas. Comfortis was used to treat your pet, so any new fleas that come in would be destroyed before they can lay eggs that could infect your home. Comfortis should be used consistently each month to stop further flea infestations.

Fleas that are present in the environment can continue to bite your pet. To help control the flea population, it’s crucial to treat all family pets with an approved flea treatment.

What Should I Discuss With My Veterinarian Regarding Comfortis For My Dog

The greatest pharmaceutical advice can be given by your veterinarian, who is an expert in caring for your pet’s health. This covers the prevention, control, and/or treatment of parasites like intestinal parasites, heartworms, and fleas. These parasites have been linked to heart problems, anemia, and illnesses including flea allergy dermatitis. Your discussion’s focal points may include:

  • The ideal time to begin flea treatment in your area.
  • Which route of administration is most suitable for your pet.
  • What to do if you forget to administer a Comfortis dose.
  • What other drugs you give your pet.
  • How to handle a severe flea infestation.
  • What actions you may do to keep your home from becoming infested with fleas again.

Comfortis® Storage

Comfortis® should be kept in a regulated environment with a temperature range of 68 to 77°F. Temperatures between 59° and 86°F can be tolerated for short periods. To preserve the chews from moisture and light, store the medication in the blister packs provided until it is time to use them.

Keep out of children’s and pets’ reach.

Alternate Flea Treatments

Other over-the-counter topical preventives, such as Frontline Plus, are available to both cats and dogs and treat current infestations as well as help prevent those from happening in the future if Comfortis is not an appropriate option for your dog.

Pets with infestations of insects other than fleas may also need a stronger treatment. If your dog has a tick infestation, K9 Advantix II provides comparable flea protection while also getting rid of the ticks. It may be easier to provide a single drug that addresses both flea infestations and internal parasites for the treatment of intestinal parasites spread by fleas and ticks. Other prescription drugs, including Revolution, can achieve this. Always consult your vet before administering any drug to your dog.


How can I reduce the risk of side effects?

Make sure to administer Comfortis to your dog per their weight to minimize the risk of side effects. To help lower the risk of digestive upset, it’s also crucial to administer Comfortis with food. Before giving your dog Comfortis, discuss with your veterinarian any history of seizures or other health issues.

Should I use a flea collar or topical flea treatment with Comfortis for dogs?

No, topical flea treatments are not essential because Comfortis completely eradicates adult fleas and stops the life cycle of fleas. Certain additional drugs may have negative side effects when taken with Comfortis.

How long do the side effects of Comfortis last?

The majority of Comfortis’ adverse effects are minor, transient, and disappear within a day or two. However, it’s crucial to seek medical care immediately if your dog suffers more serious side effects like seizures or trouble breathing.

Are there any Comfortis in dogs long-term side effects?

There is no proof that Comfortis has any negative side effects in the long term for dogs. However, Comfortis should be taken with caution, as should all pharmaceuticals, and it’s crucial to keep an eye out for your dog’s health issues or indicators of any adverse effects.

How can I tell if Comfortis is working for my dog?

You should notice a decrease in flea activity within 30 to 60 minutes of giving Comfortis to your dog. Additionally, your dog ought to feel less uncomfortable and itchy. Contact your veterinarian for more advice if you find flea activity persisting or if your dog is still itching and in discomfort.

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