Can you split parasite prevention?

Last updated 13 DECEMBER 2022

This article is written by Pet Circle Veterinarian, Dr Carla Paszkowski

As vets, a common question we get asked is 'can I split my pet's parasite prevention in half?' There are a few reasons why a pet owner may wish to split their parasite prevention tablets or chews, and instances when it may be appropriate, and others when it is not.

Read on for more information about splitting parasite preventatives.


1. Reasons why pet owners want to split tablets

2. Instances when you can split

3. Instances when you can not split

4. Why they say not to split: what can go wrong?

Reasons why pet owners might want to split tablets

1. Cost saving; many people with small dogs, or multiple animals in the house, may want to buy a large dog chew and split it between their pint-sized pups. Maybe your dogs are different sizes, and it seems more affordable to buy one packet, rather than multiple? Or maybe you have one pooch, and want your pack to last twice as long?

It's easy to assume that if you have a small dog who weighs 5kg, you should be able to buy a tablet for a 10kg dog and halve it; especially if the medication dose seems to line up as an even double. However, manufacturers usually advise against this, except in certain circumstances. See below for more about this.

2. Easier dosing; perhaps you don't intend to divide the dose, but you just want to split a chew into smaller pieces so it is easier to give. Or maybe you want to crush a tablet into something palatable, such as wet food, so your pet will accept it. In general, this is usually fine so long as you can guarantee your pet will receive the entire dose. However, there are certain circumstances where this is not advised. An easy way to check is by looking at whether the medication is meant to be chewed or not. A chewable medication will be crushed up by the time it reaches the stomach anyway, whereas some pills or capsules may need to be given whole, with an intact outer membrane. Note - this only applies to parasite prevention. If you wish to crush another type of medication into food, such as pain relief or antibiotics, we recommend you check with your vet beforehand.

Instances when you can split

Firstly, let's talk about when it is okay to split your dog's parasite prevention chew, tablet or topical treatment.

You can split pills if:

  • The tablet is 'scored' with a clear graduated line down the middle - this is a sign that the manufacturer created the medication to be 'okay to split'. A split line also makes it easier to break evenly, reducing the risk of over or underdosing.
  • The medication comes with instructions for splitting - this is commonly seen with some brands of wormers such as Drontal tablets or Milbemax.
  • You are able to use the remaining portions within a reasonable time frame. Many tablets will disintegrate when they are removed from their packet and broken. In some cases, this can reduce the efficacy of the medication.
  • You intend to give the whole dose, but just want to split the medication into smaller pieces to make it easier to give. For example, if your dog or cat won't eat a chew, or a tablet is too large, it usually fine to split it into smaller pieces or crush it into food, so long as you can guarantee that your pet receives every part. However, as mentioned before, this only applies to parasite prevention. If you wish to crush another type of medication into food, we recommend checking with your vet first.
  • You have been instructed by your vet to do so. This may be the case with some topical applications, such as Revolution, which can be dosed in partial amounts to small pocket pets such as rabbits or guinea pigs.

Instances when you should not split

You should never halve medication if:

  • The medication is not 'scored' with a clear graduated line down the middle. Most chewy medication does not contain a 'score' line and is intended to be eaten whole.
  • The medication has different packet sizes for specific weight ranges. If the brand produces a weight range for 'small dogs' and another for 'large dogs' it's always best to stick to the range that suits your pet.

Why can't some parasite preventatives be split?

Manufacturers provide a number of reasons why you shouldn't split medication that isn't scored with a clear line. These include:

1. Uneven dosing - if the medication doesn't contain a scored line, there is no guarantee that the medication will be evenly halved when you break it - no matter how careful you are. This increases the risk of over- or under-dosing.

Overdosing your pet can potentially lead to adverse affects, while underdosing can put your pet at risk of potentially fatal parasite infection.

2. The distribution of medication within the preventative product is not guaranteed. Many drug manufacturers cannot guarantee that the active ingredient is evenly distributed throughout the inner core of the chew or tablet. So, even if you split a chew evenly, the amount of active ingredient may not be present in even amounts in each half.

This is particularly important with chews that contains more than one drug - for example, flea and worming combinations that contain one medication for fleas, and another for worming.

While in theory halving the tablet should provide your pet with an equal half of the medication, studies and tests have not been performed for most brands to prove even distribution.

3. Tablets may be designed to be given whole and unbroken for slower release. Many medications are coated in a special layer, which slows the speed of drug release. If you break a medication's outer layer, you could be affecting the pharmacological properties. This has the potential to make the drug ineffective, or - worst case scenario - it may put your pet in danger.

There currently aren't any parasite preventatives designed for slow release, but this does prove a good point about how pharmacology is a complicated science, and why we should always follow to the advice of manufacturers!

Still not sure? If you have any questions about specific products, feel free to Ask one of our in-house vets

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Further Reading

Want to read more? Check out our other articles:

Which Flea or Worming Product Do I Need?

What is the Best Heartworm Treatment for Dogs?

How to Get Rid of Fleas in Cats

Complete Guide to Cat Parasite Products in Australia

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