Interceptor for Dogs and Cats: Uses and Differences
By Dr. Zubair Khalid, DVM, MS, PhD ·
This article is educational and is not a substitute for veterinary diagnosis or treatment.
If you have ever stood in a veterinary clinic holding a box of Interceptor and wondered whether the dog version could be split with your cat, the short answer is no. Interceptor for cats and dogs comes in separate formulations, and the two are not interchangeable. The active ingredient is the same family of drug, but the strength, the flavoring, and the approved parasite list differ by species.
Quick Answer
- Interceptor is a monthly oral parasite preventive built around milbemycin oxime, a drug that kills certain worms and prevents heartworm disease.
- The dog and cat products are different formulations. Never give a dog tablet to a cat or a cat tablet to a dog.
- Interceptor for dogs covers heartworms, roundworms, hookworms, and whipworms. The cat version covers heartworms, roundworms, and hookworms.
- Your veterinarian sets the dose from your pet's exact weight, so a 12 pound cat and a 12 pound dog do not get the same amount.
- Give it with a meal or right after eating if your pet's stomach is sensitive, and call your veterinarian if a dose is missed or vomited.
What Interceptor Is and What Veterinarians Use It For
Interceptor is the brand name for a chewable tablet containing milbemycin oxime. It belongs to a class of drugs called macrocyclic lactones, which are widely used in veterinary medicine to control internal parasites. In the United States, it is sold as a prescription product, which means a veterinarian has to examine your pet and authorize the purchase.
Veterinarians use it for two main jobs. The first is heartworm prevention. Heartworm disease is caused by Dirofilaria immitis, a mosquito-borne parasite that lives in the pulmonary arteries and heart. Monthly preventive drugs stop the larval stage from developing into adult worms. The second job is treating and controlling common intestinal worms. Which worms depends on whether your pet is a dog or a cat.
Milbemycin oxime also appears in combination products. One formulation pairs fluralaner with milbemycin oxime for dogs, and researchers have studied it for preventing and treating canine angiostrongylosis, a lungworm infection [1]. That is a different product from Interceptor, but it shows how the same drug can be combined with others for broader coverage.
If you are also sorting out flea control, our guide to flea prevention for dogs and cats walks through the options.
How Interceptor Works
Milbemycin oxime interferes with the parasite's nervous system. It opens channels in nerve and muscle cells that let chloride ions flow in, which quiets the nerve signals the worm needs to move and feed. The parasite becomes paralyzed and is cleared from the body.
This mechanism explains why the drug works against several different worms at once. Heartworm larvae, roundworms, hookworms, and whipworms all depend on similar nerve signaling. It also explains why the drug does not treat every parasite. Tapeworms, coccidia, and giardia do not respond to it, so a pet with those infections needs a different medication.
One practical point about heartworm prevention. These drugs work on the larval stage, not on adult heartworms. That is why testing before you start or continue a preventive matters. Giving a preventive to a dog that already has adult heartworms does not cure the infection.
Interceptor for Dogs and Cats: The Differences That Matter
This is the part owners most often get wrong, so it deserves its own section.
Different Species, Different Products
Interceptor for dogs and Interceptor for cats are manufactured as separate products with different tablet strengths and different flavor bases. The cat version is formulated for cats specifically. The dog version is not.
Cats metabolize some drugs differently than dogs do. Giving a cat a dog-sized dose of a macrocyclic lactone can cause serious neurologic signs. Even when the milligram amount looks similar on paper, the approved product for the wrong species is not a safe substitute.
Parasite Coverage Differs
Interceptor for dogs covers four parasites, heartworms, roundworms, hookworms, and whipworms. Interceptor for cats covers three, heartworms, roundworms, and hookworms. Whipworms are not a routine concern in cats, so the cat product does not carry that claim.
Hookworms deserve a note. A study of a Labrador breeding kennel in Georgia found that milbemycin oxime reduced hookworm fecal egg counts by only 43.9 percent, while a topical emodepside plus praziquantel product for cats achieved a 100 percent reduction in that same group of dogs [2]. That study used an extralabel product in dogs, so it does not mean you should reach for a cat product. It does mean hookworm resistance is real in some regions, and your veterinarian may want to recheck a fecal sample after treatment.
Cats Can Get Foreign Parasites Too
Cats adopted from other countries can carry parasites that are unusual in the United States. One report described a cat imported from Thailand with multiple infections, including a lungworm larva identified as Oslerus rostratus. That cat was treated with a two-day course of milbemycin oxime at 10.7 mg/kg combined with praziquantel at 26.8 mg/kg [3]. Notice that this is a specific, veterinarian-directed protocol for a complicated case, not a dose you should copy at home. It also shows why a fecal exam and a travel history matter.
Dosing Basics
Who Decides the Dose
Your veterinarian does. The dose depends on your pet's weight, age, health status, and the parasites you are trying to control. Do not split human medications, do not guess from a previous pet's prescription, and do not use a friend's leftover tablets.
How It Is Given
Interceptor is a chewable tablet given by mouth, usually once a month. Many pets take it willingly because it is flavored. If your pet is picky, you can offer it with a small amount of food. Giving it with a meal can reduce the chance of an upset stomach.
What to Do About a Missed Dose
If you miss a dose, give it as soon as you remember and then return to your regular monthly schedule. If more than a month has passed, call your veterinarian. They may want to test for heartworm before restarting, because a gap in prevention leaves room for infection.
What If Your Pet Vomits
If your pet vomits shortly after taking the tablet, you may not know how much was absorbed. Call your veterinarian for advice. Do not give a second full dose on your own.
Side Effects
Most pets tolerate Interceptor well. When reactions happen, they are usually mild and short lived.
| Side effect | How common or serious | What to do |
|---|---|---|
| Vomiting, diarrhea, or drooling | Uncommon, usually mild | Offer food with the next dose. Call your vet if it continues past a day |
| Lethargy or decreased appetite | Uncommon, usually mild | Monitor for 24 hours. Call if your pet seems dull or will not eat |
| Itching, hives, or facial swelling | Rare, potentially serious | Call your veterinarian right away or seek emergency care |
| Tremors, wobbling, or seizures | Rare, serious | Treat as an emergency. Call your veterinarian or a pet poison control service now |
| Weakness or collapse | Rare, serious | Emergency care immediately |
Neurologic signs are the reaction veterinarians worry about most with this drug class. They are more likely in pets that receive too high a dose, in small pets given a large-pet product, and in some herding breeds with a specific genetic sensitivity. Tell your veterinarian your pet's breed and any prior reactions.
Who Should Not Take It and What Interacts With It
Puppies and kittens below the labeled minimum age and weight should not receive it. Pregnant or nursing pets need a veterinarian's decision, not an owner's guess. Pets with a known allergy to milbemycin oxime or related drugs should not take it.
Use caution in pets with liver or kidney disease, in pets that are debilitated, and in herding breeds with a history of ivermectin sensitivity. Your veterinarian may adjust the plan or choose a different product.
Drug interactions matter. Macrocyclic lactones can add to the effects of other drugs in the same family. If your pet is already on a heartworm preventive, a flea product, or a dewormer, tell your veterinarian everything, including over-the-counter products. Do not stack two preventives that contain the same or similar active ingredients without veterinary guidance.
Overdose and When to Call for Help
An overdose can cause vomiting, drooling, wobbling, tremors, or seizures. If you think your pet ate extra tablets, or ate another pet's medication, act right away. Do not wait for symptoms.
Call your veterinarian or an animal poison control hotline immediately. Have the product name, the strength on the label, how many tablets were involved, your pet's weight, and the time it happened. Do not induce vomiting unless a veterinarian tells you to.
If your pet is having a seizure, cannot stand, or is struggling to breathe, go to an emergency clinic now.
Limitations and When to Contact a Veterinarian
No preventive covers everything, and no article can replace an exam. Contact your veterinarian in these situations.
Same day: vomiting that will not stop, drooling, hives, facial swelling, or a dose that was missed by more than a few days.
Emergency now: seizures, tremors, collapse, trouble breathing, or a known overdose.
Routine visit: yearly heartworm testing, a fecal exam, a new pet's first preventive plan, a move to a new region, or any pet with a history of hookworm infections that keep coming back. Resistance to dewormers has been documented in the United States, and a fecal egg count reduction test can show whether a product is still working in your area [2].
If you travel with your pet, plan refills ahead of time. Our article on flying with a dog or cat covers airline rules and carrier requirements.
If you are bringing a new cat and dog into the same home, parasite prevention is only one piece. See our guide to introducing dogs to cats for a step-by-step approach.
Frequently Asked Questions
Can I give my dog's Interceptor to my cat?
No. The dog and cat products are separate formulations with different strengths and approvals. Giving a cat a dog product can cause serious neurologic side effects. Call your veterinarian if this already happened.
Does Interceptor prevent fleas or ticks?
No. It targets internal parasites only. Fleas and ticks need a separate product, and many pets do well on a combination plan chosen by a veterinarian.
Why does my veterinarian test for heartworm before refilling the prescription?
The drug prevents heartworm larvae from maturing, but it does not kill adult worms. Testing confirms your pet is negative before you continue. This protects your pet from a reaction and keeps the prevention plan accurate.
My pet has been on Interceptor for years with no problems. Do I still need yearly tests?
Yes. Yearly testing is standard practice for pets on heartworm prevention. It catches infections early and confirms the product is working. Your veterinarian may also recommend periodic fecal testing.
What should I do if my pet spits out the chewable tablet?
Do not force a second full dose. Try offering it again in a small treat, or ask your veterinarian about an alternative form of the same medication. If you cannot tell how much was swallowed, call the clinic for guidance.
Is Interceptor safe for puppies and kittens?
Only at the age and weight listed on the label, and only under veterinary direction. Young pets are dosed carefully because their bodies handle drugs differently. Your veterinarian will confirm the right starting point.
Can I use Interceptor if my pet is on another dewormer?
Sometimes, but it depends on the products. Two drugs from the same family can add together. Tell your veterinarian every product your pet receives, including supplements and over-the-counter items, before you combine anything.
Related Articles
- Flying With a Dog or Cat: Airline Rules, Carriers, and Cabin Requirements
- Introducing Dogs to Cats: Prey Drive Assessment and Desensitization
- Flea Prevention Dogs Cats
- Flea Prevention for Dogs and Cats: What Owners Should Know
- Behavioral Modification Techniques for Exotic Pets
- Automatic Cat And Dog Feeder
- Interceptor for Dogs: Ingredients and How It Works
- Interceptor for Cats: Side Effects, Sizes, and Dosing
- Interceptor Dewormer for Cats: What It Treats and Safety
- Canine Heartworm and Flea Prevention: Understanding Combined Products
References
- Efficacy of a single oral administration of a formulation of fluralaner, moxidectin and pyrantel (BRAVECTO® TriUNO) in dogs for the treatment and prevention of angiostrongylosis. Parasites & vectors, 2026.
- Multiple anthelmintic drug resistance in hookworms (Ancylostoma caninum) in a Labrador breeding and training kennel in Georgia, USA. Journal of the American Veterinary Medical Association, 2022.
- Clinical co-parasitic infections in a cat imported from Thailand. The Canadian veterinary journal = La revue veterinaire canadienne, 2026.