Splitting Vials: Risk Minimising

Many pet owners, jack of extortative pricing,  are defying the recommendations of drug manufacturers and vets, and  working-out ways to economise.  When tick season arrives and monthly application  of spot-on is no longer enough, owners of smaller dogs and cats are grabbing the syringe, doing the math, and splitting vials intended for use on much larger animals.  Cutting the cost of some treatments by up to 90%, suddenly the crippling financial burden of fortnightly spot-ons seems affordable to most.  Those with dogs over 25kg are unable to rort the system.


For decades, this type of ‘off-label’ use of over-the-counter medication has been commonplace on the farm where bulk volumes of argicultural chemicals intended for herds of sheep and cow have been used for parasite control in the farm dog.

This may sound dangerous, and it’s true, breaching manufacturers instructions voids their liability, but vets are doing exactly the same thing when we prescribe human medications to pets in the clinic. As long as sufficient research is done  to ensure the drug isn’t uniquely toxic to a particular species, and the dose is calculated accurately, there’s little risk.

Warnings against such consumer behaviour by vets and Big Pharma aren’t only commercial self-interest. We are regularly called to advise and treat in cases of overdose and toxicity. Given some Dog-Only supermarket products and Advantix® can kill a cat, it’s understandable that the industry, including myself, cannot recommend vial splitting. The more people doing it, the more mistakes will inevitably occur.

That being said, in the interests of harm-minimisation, here are some very important points on splitting spot-on treatments, for those insistent on defying our recommendations.



Even the most experienced and dextrous of users will risk getting a certain amount of product on their hands. Unless you’re blase about handling chemicals, it’s worthwhile using gloves when drawing insecticide into syringe, especially with Advantix®. You’ll need a needle or fine, stiff tube to act like a straw. There’s the obvious risk of stick injury to human, but remove the needle before applying to pet’s skin. You don’t wanna inject kitty with insecticide, no matter how desperate you are to eradicate fleas.  Applying doses to the pet are less messy and can usually be done safely by bare hand.



Manufacturers packaging protects the product from 2 important things: light and air. Drugs and insecticides can be destroyed and rendered ineffective if mishandled. Keep in the syringe, expel all bubbles, and store in a cool, dark place. Fridge is ideal, but under the sink or other ‘chemical repository’ is ok. Airtight tupperware is best as some of these insecticides are volatile. Revolution is very volatile and must be stored chilled once packaging is breached. Do not freeze.



Spliting  vials only saves money if dividing a large dog vial for use in smaller pets. These large vials will contain anywhere from 2 to 4mls of product, depending on brand. If treating a cat or small dog there may be as many as 8 to 10 treatments in each large vial. You will need an appropriately sized syringe to draw-up the entire contents of the vial, with sufficiently fine gradations to give a correct dose.

If a syringe has been in the fridge for a while, gently move the plunger to ensure it’s sliding freely before applying to pet. Sudden release of a stiff syringe may result in accidental overdose.

There  are some variations in formulation between cat, puppy and adult dog formlations. The most notable are:

  • Frontline Plus® for dogs has less (L)-methoprene than that for cats. Using a dog formulation on a cat will underdose this ingredient. An insect growth regulator, methoprene effects development of the baby fleas and may reduce long-term flea control, but not anti-tick efficacy.
  • Advocate® for dogs has more moxidectin than that for cats. Using a dog formulation on a cat will overdose with this agent. Advocate®  can be safely split for use on small dogs but  is risky in the cat.  Symptoms of moxidectin overdose in a cat may be gasrointestinal or neurological. A case report of a cat afflicted with similar clinical signs is described at CSI Bangalow: Spiked Custard?
  • Revolution® has a single active, safe in both cat and dog, but it’s concentration varies: the formulation for puppies, kittens and cat is half strength. If splitting a large dog vial and applying the volume stated on the packaging for a cat, a double dose would be given. Take careful note of the half volumes shown below.
  • Advantix® just to say it again – NEVER USE THIS ON CATS. If you get Advantix® on your hands when splitting a vial for the dogs, do not touch your cat before thoroughly washing your hands with warm soapy water.


Justifications for Vial Splitting

There’s a number of situations described below, when economising on flea control is most imperative.  If you’re going to split vials and massively slash your annual flea and tick control bill, please exploit the opportunity this saving provides.  Splitting vials and then miserly using products infrequently to economise further, is not going to engender sympathy when your pet presents at the clinic with flea allergy or a tick.

1. Financial Hardship – those who question ‘Why should someone who can’t afford to treat their pet be allowed to have one in the first place‘ are neglecting to acknowledge that pets can live for more than a decade, and our financial situation can change.  Some can’t stand seeing homeless dogs euthanased and take on more than they can provide for.  Stating ‘pets are a luxury item’ is ignoring the reality that, unless we assets-test and regulate pet ownership like child adoption, all economic strata will continue to seek animal companionship, irrespective of resources. Vial splitting may at least make the lives of the poor more comfortable.

2. Tick Season –  application of Avantix® or Frontline® every 2 weeks during a 6-month tick season is cost inhibitive for many. Stretching out the treatment interval to 3 weeks runs the risk of a case of tick paralysis that can blow the budget even more severely. Splitting vials may save lives in  this situation. For more see Tick Prevention: Cost versus Benefit

3. Flea Allergic pets, like those of us allergic to mosquito bites,  will incessantly itch and pull out all their hair if just one flea gets past the flea control. Given most spot on agents only achieve high kill rates, above 95%,  for the first 2 weeks of the month, fortnightly application is often recommended by dermatologists when treating flea allergy. This is cost inhibitive for many, especially if you need all year round protection in warmer climates. For more see the links below.

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30 Responses to “Splitting Vials: Risk Minimising”

  1. troyvanjohnson says:

    Fuck ur good!

  2. Kelly says:

    What a FANTASTIC post!

  3. lissa says:

    thank you. this has been a life saver for me and my roomate and our dogs

  4. thanks for the tip! says:

    I like the economy of this as I have a vsmall dog and a large one

  5. Jan says:

    This is really helpful especially for shelters. We live in Brazil and fleas multiply quickly here. They are also resistant to many products including Top Line. I am now trying Revolution which we received as a donation and will be splitting some for the smaller dogs. I will measure it carefully and wear gloves. Thank you

  6. Paula says:

    Hands down the best article about the subject. Simple and easy too. THank you!

  7. Amy says:

    Thank you! I accidentally ordered the over 55 size of Advantix when I needed the next size down and opened the package before I realized…then I remembered something about the possibility of splitting vials and a quick google search led me here so I could still dose my dogs properly. Appreciate it!

  8. Marvin Von Renchler says:

    I believe this is incorrect. If you take each size vial and divide it by the maximum pounds of dog, it comes out to . 305 per pound of body weitght. The extreme difference in ml between the up to 55 and over 55 means that at 68 pouinds you are doubling the dose needed or more. I use a 1ml (cc) syringe and use .o305 per pd and its been working well for years. Especially on tiny dogs like chihuahuas which are delicate anyway and more likely to have allergic reactions to this med. Do your ownm math in case my memory is bad The ml of the dose divided by the max weight for its vial color/size.

  9. admin says:

    hi there, i’m not caluclating on a mg/kg dose rate, but simpply using the dose rates recommended for the body wt ranges as described by the manufacuturer.

    Its possible that you may be able to titrate doses further by dividing by the dose for the maximum body size, but this may compromise efficacy. This is no big deal for fleas but could be life threatening for paralysis tick prevention.

    Allometric scaling (the increasing dose rate for drugs, per kg, as body wt to surface area decreases) needs to be considered also. All to complex for my ageing brain.


  10. Ness Reeeve says:

    I’ve converted so many people to vial splitting with only positive results.

    I have 2 pugs weighing about 6 kg’s each. I buy my Frontline Plus for 40-60 kg dogs online (www.budgetpetproducts.com.au) as it’s about half the price of a pet shop or vet.

    I use half a ml on each dog every 14 days (as the tick problem is bad where I live in Northern NSW).

    We don’t have a flea problem and have never had a tick since using this, plus no adverse reaction from the dogs in any way.

    One vial for a 40-60 kg dog lasts me for 10 treatments and the pack lasts for months.

    I do believe it will only work if you are diligent about using the treatment exactly as recommended – every 14 or every 28 days, not a day or 2 late.

    Vial splitting in addition to buying the treatments from the net saves me hundreds of dollars a year and more importantly ensures my dogs are always healthy and happy!

    By the way Matt is the best vet on the planet xx

  11. When dealing with fiddly Revolution doses under 0.30ml – such as treating a 3kg chicken or cat… 3kg = 0.15ml Dog Revolution.
    Simply squirt 0.15ml into a vial, then add an equal amount of IPA (rubbing alcohol) to dilute the solution 50:50 — Now you have 0.30ml to work with (instead of a pissy 0.15ml) which is much easier to work with, especially if you are trying to get it ALL on the skin, and not on fur or feathers!

  12. jackie e. london says:

    I would never have thought of doing this, were it not for this article.. I have two dogs, I was made redundant recently, so I am looking to cost save. My vet fees for advocate are double the online price, and they want £12 to write a prescription.. This is crazy for people who are strapped for cash. I have since ordered a larger size online, and ordered some blunt syringes so I can apply the correct dosage.. I have saved myself over £25.00 for using one packet versus 2…

    Thanks again for the advice!

  13. Kytti says:

    Great page. One note with Revolution, even when halving the amount of dose to account for the difference in concentration between cat Revolution and dog Revolution, we have found that the dog formula is too strong for the more sensitive skin on cats and may leave a hairless or even burned scabby spot on the cat where applied.
    Unless you are experienced with compounding medications and can dilute the dog Revolution with a safe and effective carrier so that it’s more like the cat formulation, I don’t recommend splitting Revolution. However we split Advantage and Advantage II all the time! With as many as 9 fosters in a home, it’s really a money saver for rescues!

  14. Dara says:

    Has the Advantage formula changed? Since I found this post I’ve been splitting vials of Advantage for the past few years between our cats and dogs without any problems. However, on the new box it says “DO NOT USE ON CATS”. The active ingredients are the same and inactive ingredients are now conveniently located inside the box so I can’t compare in store. I wonder if it’s just a marketing ploy or is it actually different?

  15. admin says:

    sounds like a tactic to deter vial splitting. If the sole ingredient is imidacloprid, it would be safe to use on cats.

  16. Sheila says:

    Really good information. I’ve been splitting the extra-large vials of Frontline Plus among our three dogs for quite some time now without any problems. I do have a question, though.

    I’m in the U.S. The extra-large Frontline Plus is for dogs from 89 to 132 pounds and this is what is printed on the front of the box. There are quite a few boxes of Frontline Plus which state that the vials are for dogs from 40 to 60 kilos. The boxes stating the weights in kilos always cost less than the ones with the weights stated in pounds (at least on ebay), and one site which sells this product imported from Australia states that the Australian product has not received the American EPA seal of approval and, from the sounds of it, they are not even supposed to be sold in the U.S.

    Since 40 kilos is 88.1849 lbs and 60 kilos is 132.277 lbs, and the amount of the solution in the vials in both boxes is the same, could the problem be in the amounts of the individual components that make up the solution? If you do know what the difference is between the product made in Australia and the one with our EPA seal on it, I’d much appreciate your passing on this information.

    Thanks very much.

  17. To the poster above me… April 23, 2014
    AU and US Frontline are both made in the same factory in France. They are the exact same thing. eBay sellers try to state that the AU version is fake, is not approved by the EPA etc.
    They only say this so that they can scare you away from buying the cheaper AU Frontline.
    Yes, the AU version is not approved by the EPA, but that is simply because it is not supposed to be sold in the US. Why approve something that is not even sold in your country (normally).
    Kelly – From Australia.

  18. Kat says:

    To Kytti, one of the other posters (Kelly) supplied information on diluting Revolution in Rubbing alcohol, as a means of making measuring easier. This would also dilute the formula to make it less irritating to the sensitive skin of cats. If you know what the total volume is of the vial you are working with, then just add the equivalent amount of rubbing alcohol to the vial (or mix in a syringe/small container), and then you have the equivalent strength per mL as the cat formula of Revolution (which is half that of the dog Revolution). As for the Advantage formula changing, check online for the ingredients. Their website should tell you. It may be that they are trying to put people off vial splitting. Or it could be a safety precaution because people often get Advocate, Advantage and Advantix mixed up – dog Advocate should not be used on cats, except perhaps as a once off, or for tick only control, not fleas, and you’d have to underdose (reason given on this website), and Advantix is toxic for cats.

  19. Liz says:

    Thank you for this awesome information, I already bought frontline 40-60kg for my 2 dogs and split the vial between them, then panicked for the next 24hrs. This has really put my mind at ease that I have not poisoned them. thanks again

  20. Sam Buck says:

    Very useful page. We’ve used the same vet for my cat for 6 years and have been using advocate flea treatment. My mum went and purchased some over the counter and asked me to do the cats treatment tonight, (4-8kg cat) only to find that they had given us the treatment for an extra large 20-40kg dog!!! Had I not checked or had my mum not asked me to do it, from reading this page I can now see what effects it would have had on her! So angry, they will definitely be hearing from me tomorrow. Thank you!

  21. Kathy Cobb says:

    Actually, the new Advantage Multi is a different formula for cats and dogs. Therefore, DO NOT USE Advantage Multi for dogs on cats.

    However, Advantage II and the older Advantage formulas are the same formula. But be extremely careful to measure out the proper dose. If you get confused by simple math, have someone else there to be sure you get it correct.

    It is a mistake you only get to make once, so be careful. However, as long as you give .4 (point 4 ml, not 4 ml) to cats 9lbs and under, and .8 (point 8 ml, not 8 ml) to cats over 9 lbs, you should be good to go.

  22. Lisa says:


    I have a similar question as above: I’ve been splitting Advantage for years and recently can only find Advantage II and see huge warnings all over the box not to even let your cat touch a dog that has been treated with it. There seems to be an additional ingredient called pyriproxyfen in it…breakdown is 9.10% imidacloprid, 0.46% pyriproxyfed and 90.44% other ingredients for a total of 100%. How can we be 100% sure that Advantage II dog formula in bulk is safe for cats and dogs with these new warnings. I want to keep buying in bulk but I don’t want to risk my cat. Please help!!

  23. admin says:

    Yes, advantage II is a new product with new ingredients and you should heed the label warnings. This matter will continue to cause confusion and risk and will probably necessitate removal of this resource.

  24. Jacqueline says:


    Thanks for all the interesting and informative information.

    I too have a question related to the above: the ‘Advantage II large dog’ I just purchased online does not carry the same box or pamphlet warning mentioned above, though I have seen a cat warning and cat drawing on a Bayer (online) pamphlet; but under ‘how to apply’, my pamphlet does say: “Use only on dogs. Do not use on other animals.” My ingredients are exactly as above, w/ the exception that mine says ‘pyriproxyfen 0.46%’ not ‘pyriproxyfed 0.46%’ (typo perhaps?). After a heavenly, flealess -but not tickless- 6 months in the Swedish countryside, our year-old cat is now in southeast FL’s flea-heaven (fortunately, not permanently), thus I am somewhat confused as to how many Advantage II formulations and labels there are out there, since Frontline Plus no longer worked for him? Many thanks.

    On another note: his ISO microchip failed sometime between Nov. 2014 and Feb. 2015 (Swiss manufacturer, but inserted in US in Sept. 2014); it was successfully scanned several times before his trip to Sweden, but couldn’t be detected by several vets there nor by the same US vet upon his return to the states. The latter vet said she’d never heard of failures, but ruled out chip migration and chip exit because these tend to happen w/in the first month, and the vet that supplied the Swiss microchip said that vets aren’t required to report failures. Hence the % of chip failures is, alas, an unknown to honest consumers, yet we hear that chipping has allowed for a growth in animal trafficking in Europe, where chipping is required by law.

  25. admin says:

    hi jac, unfortunately i cant recommend using the advantage II on cats. In relation to product failure, its never absolute. The kill percentage will gradually trend down as resistance emerges, down from 90+% to 50% or lower. Once its below 70% most owners report it doesnt work at all, unaware how bad the fleas and ticks would be with no product at all. Increasing dose(eg fortnightly), within limits, can boost efficacy, but its a short term victory. Spinosad/Comfortis is now registered for use in cats, but its a big pill and some cat owners have difficulty getting it down. Because its new, its very effective.

    I havent enountered a chip failure but i’m sure its possible. Chip readers can be temperamental and low batteries can effect performance, and some will only read certain brands or types of chips, so i would definitely try to get it read again at the hospital that implanted it.

    good luck

  26. J Stein says:

    Hello Dr Matt,
    Thanks for writing this informative article. After trying different anti flea medicines for my cat I finally found something that works…selamectin. I poured contents of 1st packet of 2cc Stronghold pipette into an empty prescription bottle , drew .38cc out w/syringe, applied to my cat, and stored remaining 4.62cc in prescription bottle in frig.
    One month later, I went to draw the next .38cc from the rx bottle in frig but there was nothing inside despite the rx bottle being completely closed. I recently found out this medication evaporates quickly.
    What’s the ingredient that makes it so volatile?
    How do I make this volatile medication stable (so it doesn’t evaporate) ?
    What is your recommended way to store the unused portion?

  27. admin says:

    hi there, yes, selamectin’s carrier is volatile, like alcohol. The only way the manufacturer gets around this issue is airtight sealed packaging. Freezing usually destroys drugs. So there is no easy solution. Ive given up dividing selamectin/revolution.

  28. Hannah says:

    Thank you so much for this post. It is so informative and really helps those on a budget but wants the best for their pets!.

    In terms of keeping the syringe in a cool, airtight, dark place (ie. the fridge). Do we cover the syringe tip with something as well? Eg. glad wrap? – to help reduce oxidation…

    Also how long would the single pipette/vial last once opened? ie. at least 6 months?

    Again, really appreciate this post!

  29. admin says:

    you could try to seal the end somehow, but its not usually necessary. I usu just leave a capped drawing needle in place. The exception is revolution, which is highly volatile andwill even evaporate when chilled. Yes, they last up to a few months at least.

  30. Robert says:

    I’ve been splitting frontline plus for dogs 89-132 lbs for years for my cats. Ends up costing 1/8 the price of cat version and works just the same. Just noticed today that Walmart is carrying Pet Armor Plus for only $27.54 and it has exactly the same ingredients.

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