The Best Kind of Flea and Tick Medicine for Dogs

Tufts University veterinary dermatologist explains how to make a decision.


There is a lot of confusion about which is the best flea and tick medicine to give a dog. A collar that emits the active ingredients slowly? A liquid-like spot-on that you apply monthly between the shoulder blades? Or a pill? And among those three choices, what are the best brands? Furthermore, should you buy your brand from the veterinarian, or is it okay to pick up at the supermarket? Then, too, are dogs prone to adverse reactions?

One reader recently wrote in to say that he usually buys his dog’s spot-on flea and tick medicine at his veterinarian’s office, but to save money, he bought it recently at the grocery store. Within a day of his applying it, his dog had the runs for several days. Could the two things have been related, he wanted to know? Did the cheaper product induce some kind of toxic reaction?

“The diarrhea was very likely a simple coincidence,” says Tufts veterinary dermatologist and Your Dog editorial advisory board member Lluis Ferrer, DVM, PhD, DECVD. “Without knowing the exact product used and its composition, it is impossible to say, but it would be very strange for a dog to develop the runs from the drug.

“What owners occasionally see with spot-ons,” Dr. Ferrer says, “is that dogs itch, so they will try to chew the spot of application between the shoulder blades or rub against the carpet for a few hours, or maybe even for a whole day occasionally.” But it’s a harmless side effect.

Still, given that some dogs want to scratch that spot on the skin once the medicine is applied, you might assume that a spot-on is not the way to go. After all, why risk making your dog uncomfortable, even if the discomfort won’t harm him?

The thing is, “each type of medicine — spot-on, collar, or pill — has its advantages and disadvantages,” Dr. Ferrer counsels. There’s no best answer. You have to weigh the situation for your particular dog. You also need to talk to your vet about it — even if you don’t end up buying a product from the vet’s office.

Speak to Your Vet Before Choosing a Flea Prevention Product

Before you even think about which type of flea and tick preventative to use, it’s very important to talk with your veterinarian, Dr. Ferrer says, because you need to make sure you’re giving your dog something that will take care of all the types of fleas and ticks in your area. You want to keep your dog protected from fleas and ticks all year round in order to prevent the transmission of infectious diseases, some of them very severe, and different formulations work for different types of parasites. Some of the medicines on the market do not cover all of the types of ticks we have in North America. There’s no point in applying the medicine if it’s not going to be 100 percent effective, and your dog’s doctor can help you on that score. The doctor can also help you to decide in which of the three available forms you want to give the medicine.

Types of Flea and Tick Control

Collar:For those who prefer using a collar, there are options that fight all fleas and ticks.

Advantages. Collars are an easy choice for people who don’t want to be applying medicine between the shoulder blades every month or giving tablets for the dog to take by mouth. The Seresto collar protects a dog from fleas and ticks for up to eight months. It is also safe for cats. This is an important point for homes that have both dogs and cats because cats are very sensitive to some of the treatments commonly used for dogs. You can never assume that a product that is safe for dogs is also safe for cats.

Disadvantages. Such collars are expensive, relatively speaking, so you have to lay out more money at a time. In addition, if you lose the collar, you’re back to square one.

Also, bathing can reduce the duration of the collar’s effectiveness. In order to maintain an eight-month duration, for example, dogs must not be bathed more than once per month. For dogs that swim more than once a month, the duration of control against the parasites is reduced.

Occasionally, a slight itching may be observed in animals that are not used to wearing collars in the first few days after fitting. In a very small percentage of cases (probably less than 1 percent), a mild dermatitis due to mechanical or chemical irritation of the collar may occur at the application site, which usually recovers within one to two weeks without the need for collar removal. Still, in these cases, the collar is probably not the best preventative choice for the dog.

Another very effective and safe collar for dogs is Scalibor Protector Band. It provides up to six months’ protection against ticks and fleas, with the same caveats as described above.

Spot-on:There are some really good brands of spot-ons. Among the choices: K9 Advantix, Frontline Plus, Activyl Tick Plus, and Vectra 3D. The companies that manufacture these products have proven safety and efficacy with scientific studies that were published in peer-reviewed journals, meaning independent investigators without a vested interest in the products’ success checked the results and looked for holes in the write-ups before the studies were allowed to appear in academic publications.

This doesn’t mean that no other products are safe and effective. We just don’t have evidence one way or the other. The proven products cost more because it costs more to develop and execute the scientific tests they go through. But what you get in return is an assurance that they will take care of fleas and ticks.

Advantages. Once the medicine has been applied between the shoulder blades with a little pipette that accompanies the package, you don’t have to worry, as you do with a collar, that it will come off and get lost. These products also tend to be less expensive than a collar.

Disadvantages. It’s actually not a disadvantage if you stay on top of things and mark on the calendar when you last applied the medicine. But spot-ons, recommended once a month, start to undergo a decline in protection after four weeks. A dog is not completely unprotected in week five, but he’s less protected than during the previous week, and less protected during week six than during week five. You really want to make sure you apply more medication between the shoulder blades like clockwork, every 30 days. If you’re not good at keeping with a schedule, there will be a problem.

Spot-ons are also a problem for people who bathe their dogs very often or whose dogs are out swimming all the time, say, in a lake. First of all, your dog can’t be bathed two days before or after applying the drug. Most active ingredients remain attached to the skin lipids, and if you remove them by bathing, the medicine does not persist on the skin surface. After that, if you bathe the dog once during the month or let him go swimming once, that’s okay. But if your dog is often swimming or if you bathe him frequently with a medicated shampoo because he has a skin condition or skin allergy or because he has a very strong odor to which you object, you are going to be removing the active ingredient, even if more than a couple of days have passed since you applied it.

Medicated collars lose their potency when they get wet, too. But the problem isn’t as bad as with spot-ons because the active ingredients, which are stored inside the collar rather than right on its surface, are slow-release. A couple of days after the dog has been in the water, the levels of medicine in the collar will come back up again. Still, if your dog is in the water all the time, the collar is going to spend a lot of time deactivated, and the effective life of the collar will be shortened, as mentioned above.

Oral flea medications:If you prefer giving your dog tablets, some cover all kinds of fleas and ticks. Bravecto, for example, is administered every three months, while Nexgard is given once a month. Trifexis, also given monthly, covers fleas, heartworm, and internal (intestinal) parasites. It does not protect against ticks, however. It is great when fleas are the main concern but must to be used together with other preventatives to take care of ticks.

Advantages. Providing protection against fleas and ticks in pill form is probably the best way to go if you have a water-loving dog who’s often out in the water or a dog who, for whatever reason, needs frequent bathing. Water can never make the pills lose their potency. Also, the tablets are good for owners concerned about having an insecticide on the skin surface of the dog (for instance, because of close contact with children).

Disadvantages. Some dogs, like wary prisoners or hospital patients who don’t want to be sedated, will do everything not to swallow a pill that you try to force into their mouths. You can wrap it in cheese or salami, use the gentlest coaxing language you can think of, yell at the dog, or manually work to keep his jaw open with your hands, but at the end of the day, the dog will spit out the pill or just let it drop out of his mouth — over and over again until it becomes a slimy mush that you can no longer pick up without it sticking to your fingers. If that’s your dog, pills are not the way to go, even if your pal is often in the water.

It should be noted, too, that a very small minority of dogs react to the pills with vomiting or diarrhea. Reactions tend to be mild — and they are rare — but it’s something to keep in mind.

One Flea Medicine that Always Works?

For the most part, the medicines recommended here do the trick. That said, even if you choose one of the products mentioned in this article, it does not mean it’s impossible for your dog to become infested with fleas or never have a tick on his body.

If you select an appropriate product and apply it properly and still see some fleas or ticks, “you need to consider why there might have been a failure,” Dr. Ferrer says, by talking to your veterinarian.

“In the case of fleas,” he advises, “if you still see them around your dog after having given him a good anti-flea medication, you probably have a reinfestation rather than a case of resistance to the product.” There are several ways this can happen, including a severe infestation of your house with many immature flea stages (eggs or larvae — newly hatched fleas). In such cases, the situation can become “too overwhelming for the medicine,” the doctor says. This is the most common situation in which you will keep seeing fleas despite using a good product.” But it’s not the only one. The reinfestation can also come from wildlife or from roaming pets.

None of this means you are a dirty or a bad housekeeper. It means you got unlucky and may need professional help to eradicate the problem. Your veterinarian can prescribe some environmental treatments. In some particularly severe cases, you may need a professional disinfestation of the house. Once you take care of the problem in your home, the medicine will protect your dog beautifully.

In the case of ticks, Dr. Ferrer notes, “absolute protection is not easy no matter how disinfected your house. Adult fleas live on the host — the dog — where they feed and lay eggs. The eggs develop in the home environment (rugs, carpets, couch cushions), and the new adult fleas seek the adult dog or cat to live, making the problem a vicious cycle. But the entire cycle takes place in the house, so you can control it. With ticks, because they live outside and part of their life cycle takes place in the outdoor environment with other animals in the forest and such, it’s impossible to orchestrate everything that happens to them.”

This should not make you panic. It simply means, Dr. Ferrer says, that even with an excellent product, you might sometimes see a tick, often a dying tick, on your dog. However, if this happens more frequently than once in a while, he counsels, you need to review the protection your dog is getting and go over the medicine, and the frequency with which you give the medication, with your veterinarian. Maybe your pet is not getting enough of the active ingredient for the amount of infection he’s exposed to. Your vet may suggest switching to another regimen.


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