Flea and Tick Preventatives

By Joel Kaye, DVM
angell.org/generalmedicine
generalmedicine@angell.org
617-522-7282

July 2025

XX

As loving pet owners, we all want to keep our furry family members safe and healthy. Thankfully, protecting them from pesky parasites like heartworms, fleas, and ticks has become easier and more effective than ever before. Gone are the days of daily pills like Filaribits – today, we have a range of convenient options, often in a single, once-monthly chewable treat or a simple topical application.

This article will break down the different types of preventive medications available, helping you understand how they work and what might be the best choice for your beloved companion. We’ll also provide a helpful chart to guide your decision-making.

Understanding the Key Players: How These Medications Work

Different medications use different approaches to protect your pet. Here’s a look at the main types you’ll encounter:

Avermectins: Guarding Against Internal Threats

This group of medications, found in popular heartworm preventatives like Heartgard and some topical products like Revolution Plus, primarily targets internal parasites.

How they work: Avermectins act as “neurotoxins” (nerve-damaging agents) specifically for invertebrates – think insects and worms. They work by affecting specific channels in the parasites’ nerve and muscle cells, leading to paralysis and death. These channels are largely absent or function differently in mammals, making them generally safe for your pet when used correctly.

Important Considerations: While generally very safe when prescribed and used appropriately, it’s crucial to follow your veterinarian’s instructions. Side effects are rare, but can occur, especially with an overdose. In animals, signs of an overdose could include drowsiness, difficulty breathing, low blood pressure, tremors, or unsteadiness. Always report any unusual signs to your vet immediately.

Milbemycin: Another Internal Protector

Milbemycin is another highly effective antiparasitic medication found in products like Interceptor and Sentinel. It’s primarily used to prevent heartworm disease and control certain common intestinal worms in dogs and cats. Veterinarians can also use it for some mite infestations.

How it works: Similar to avermectins, milbemycin is a macrolide antiparasitic. It disrupts the nervous system of susceptible parasites, leading to their paralysis and elimination from your pet’s body.

Important Considerations: Side effects are rare and generally similar to those seen with avermectins. Your veterinarian will determine if this medication is the right fit for your pet, especially considering any other health conditions they may have.

Isoxazolines: Your Pet’s Shield Against Fleas and Ticks

Isoxazolines are a newer class of medications specifically designed to combat external parasites like fleas and ticks. You’ll find these compounds in popular oral products such as NexGard, Simparica, and Bravecto. They are highly effective against fleas, ticks, and even some other skin parasites like mites and lice.

How they work: These drugs target specific receptors in the nervous system of fleas and ticks. When the parasite bites your pet and ingests the medication, it quickly leads to paralysis and death of the parasite.

Important Considerations: While highly effective, these medications should be used with caution, or possibly avoided, in dogs with a history of seizure disorders. Always discuss your pet’s complete medical history, especially any neurological conditions, with your veterinarian before starting an isoxazoline product.

The Best of Both Worlds: Combination Products

To simplify your pet’s preventative care, many products now combine different classes of medication to offer broad-spectrum protection. For example, NexGard Plus and Simparica Trio combine an isoxazoline for flea and tick control with an avermectin (or similar heartworm preventative) in a single, once-monthly chewable.

How they work: These products offer the benefits of both drug classes, protecting against heartworm disease, fleas, and ticks with one convenient dose. They are generally very well tolerated by pets.

Important Considerations: While oral medications like these require the parasite (like a flea or tick) to bite your pet to ingest the medication, these products work very quickly. The parasite is typically killed before it can transmit diseases to your pet.

Topical Options: An Alternative Approach

Products like Advantix and Frontline are well-known topical solutions applied to your pet’s skin. These are excellent choices for flea and tick control, and some offer other benefits.

How they work: Topical medications spread across your pet’s skin and hair, acting on parasites that come into contact with the treated area. Unlike oral medications, the parasite doesn’t need to bite your pet to be affected.

Important Considerations: Topical products are generally a bit slower to kill parasites compared to some oral medications. However, a significant benefit is that many topical products also have repellent properties, which can help deter parasites from even jumping onto your pet in the first place – a feature oral medications do not offer. Ensure correct application and dosage as per instructions.

Making the Best Choice for Your Pet

With so many effective options, choosing the right preventative can feel overwhelming. That’s why a conversation with your veterinarian is so important. They will consider:

• Your pet’s lifestyle: Do they spend a lot of time outdoors? Do they visit dog parks or hiking trails?
• Their health history: Any pre-existing conditions, especially seizures or sensitivities?
• Their species and age: Some products are only for dogs, or have age/weight restrictions.
• Your preference: Do you prefer a chewable, topical, or even an injectable option (for some heartworm preventatives)?
• Local parasite risks: Your vet knows which parasites are prevalent in your area.

Remember: Consistent, year-round prevention is key to keeping your pet safe from these common and potentially dangerous parasites. Don’t hesitate to ask your veterinarian any questions you have – they are your best resource for tailored advice to protect your cherished companion.

Different medications use different approaches to protect your pet. Here’s a look at the main types you’ll encounter: