Why The Most ‘Convenia-nt’ Antibiotic May Be The Wrong One For Cats

Convenia® is the most widely used antibiotic in Australian cats. Yet despite it having major problems no owner has ever questioned my decision to use it. Hopefully after this you will.

After all, part of the reason vets use it so much is because we think you want us to.

What Is Convenia?

Convenia is a long-acting broad spectrum antibiotic called cefovecin. Once injected, it attaches to blood proteins and works for up to 14 days.

When Convenia first came on the market it was a godsend, or so we thought. Here was the answer to all those cats and dogs who just couldn’t be given pills. And to our fears that owners would miss antibiotic doses.

And in truth it is a remarkable antibiotic. It’s generally safe, highly effective and not too expensive in smaller animals like cats. For these reasons it’s changed the very nature of veterinary practice around the world.

So where’s the problem? It’s right there in the name.

Convenia Is Too Convenient

There are two good reasons why cefovecin is usually not the best antibiotic, but no others are so easy to administer. This leads are some of the following thoughts a vet might have:

  • I bet this cat is hard to give tablets to
  • I doubt this owner can give the medication any other way
  • If I use it I’m more confident that my treatment won’t fail
  • Owners prefer it when I give their animal a shot
  • My boss says I have to give Convenia for this
  • If I don’t give it, they’ll go elsewhere

And some of these could even be true. So, faulty as it is, it’s the popular choice. Even for things we just shouldn’t be using antibiotics for at all, like:

There’s also the added pressure that once we make up a vial, it needs to be used within 1 month or we throw away several hundred dollars.

So what were those two reasons it’s not so good?

1. Convenia’s Side Effects

When Convenia came on the market, vets were understandably excited. It opened up a whole new way of treating difficult cases. But fairly soon we started to hear stories of adverse reactions.

Cefovecin contains the same base structure as penicillin, and so allergies can occur. When they happen with other antibiotics, we just stop them. With Convenia, blood levels are known to persist for 65 days.

That’s an out of control roller coaster you can’t get off.

These serious reactions are rare enough that when my cat was sick, I still chose Convenia to get her better. The daily fight to get her to take the pills was ruining our relationship. But perhaps if I’d known then what I know now I would have tried harder.

2. Convenia’s Wider Effects

Nobody has ever come to me with what I am about to say. I have learnt this only by finding the information myself. It’s the silence of a guilty status quo that needs to change.

It turns out that cefovecin is a “highest priority critically important antimicrobial”. It’s supposed to be a third line antibiotic, only used after the first and second choices fail, or after culture and sensitivity testing. This is when you swab and grow a bacteria to work out which antibiotics it’s sensitive to.

A recent Australian study found that vets were only performing cultures 0.3% of the time. Even when they did they always started the Convenia before the results anyway.

I am included in this behaviour. It can be hard to convince an owner to spend the extra 100+ dollars on testing and the results take several days to get. Usually you just want to get on and treat.

Why Does It Matter?

Antimicrobial resistance affects us all. We tend to blame doctors for overprescribing, or the agricultural industries, but people in glasshouses shouldn’t throw stones. The rate of antibiotic resistance in dogs and cats is comparable to that in humans and certainly higher than farm animals.

The use of third-generation cephalosporins like cefovecin is known to lead to the development of multidrug resistant organisms in people. Convenia is probably a worse offender due to the long ‘tail’ between 14 and 65 days when antibiotics are present in the body at sub-lethal doses to bacteria. This is a boot camp for resistance.

The problem isn’t just for ‘society’. If I give your cat Convenia when I could have used a first or second line antibiotic, their resident flora will probably develop resistance too. That means important antibiotics could fail later when we really need them, even possibly for you if you pick up those bacteria.

So What Should We All Do?

The path out of this mess is actually quite simple. Here are some suggestions for cat owners:

  • Proactively tell your vet if you think you can give oral medications. We are often time-pressured so you might find you don’t get a choice otherwise.
  • Even if you think you can’t, you mostly can. Common diseases like hyperthyroidism and chronic kidney disease tell us that every cat owner can do it when the chips are down.
  • If it still seems impossible, visit my page on giving cats tablets. You’ll see that I stress the importance of roping in a second person to help, even a neighbour.
  • As a last resort, most practice nurses will give tablets or injections for no extra fee if you come down at a set time.
  • Antibiotics aren’t just tablets. Most can be made in liquid form, which is generally easier. And would you believe that giving a daily injection is easiest of all once you know how. Most recently a 90-year-old client of ours totally aced it!

For vets, who are in the driving seat it’s even easier:

  • Vets should ask owners about their capabilities and wishes. If owners want to try we should give them support from the practice.
  • We need to take a good hard look at whether some conditions really need antibiotics at all. Part of the problem here is our tendency to be risk averse (see below*).
  • If antibiotics are needed, we should ask ourselves whether we can use one of low or medium importance instead.

By saying all this I don’t want to set myself up as a saint or criticise other vets. Until recently I was using Convenia way too much, often for the wrong things. The authorities can’t criticise either until they’ve made a decent effort to get the information in front of busy vets.

After all, they’re the ones who registered it, allowed it onto the market and then stepped away.


Hardefeldt, L., Hur, B., Verspoor, K., Baldwin, T., Bailey, K. E., Scarborough, R., … & Gilkerson, J. (2020). Use of cefovecin in dogs and cats attending first‐opinion veterinary practices in Australia. Veterinary Record, 187(11), e95-e95

Norris, J. M., Zhuo, A., Govendir, M., Rowbotham, S. J., Labbate, M., Degeling, C., … & Ward, M. P. (2019). Factors influencing the behaviour and perceptions of Australian veterinarians towards antibiotic use and antimicrobial resistance. PloS one, 14(10), e0223534

Singleton, D. A., Rayner, A., Brant, B., Smyth, S., Noble, P. J. M., Radford, A. D., & Pinchbeck, G. L. (2021). A randomised controlled trial to reduce highest priority critically important antimicrobial prescription in companion animals. Nature communications, 12(1), 1-14

The National Centre for Antimicrobial Stewardship

* One problem we don’t talk about enough is the pressure vets feel to practise defensive medicine. I recently treated a limping dog whose owners told me at the outset they wouldn’t have xrays done. So I treated the dog the best I could and when the dog turned out to have bone cancer (as I suspected), they made a complaint anyway. This sort of attitude gives us very little room for manoeuvre to not use antibiotics. If we are wrong even 1% of the time, we could still be held responsible.

Have something to add? Comments are welcome below and will appear within 24 hours.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia.


12 Replies to “Why The Most ‘Convenia-nt’ Antibiotic May Be The Wrong One For Cats”

  1. My 6 year old cat recently passed away from cardiomyopathy/heart attack. She had a nonspecific immune disease that attacked her soft tissue and was on chronic steroids. She had frequent vet checkups and had never been diagnosed with any type of heart disease. 4-6 weeks ago she had a URI and my boyfriend took her to the vet, they injected her with Convenia. Since the shot she had lethargy, shortness of breath/congestion and diarrhea. I’m convinced she died of Convenia induced cardiomyopathy. Is this a possibility?

    1. Hi Lovereet. It almost sounds like you are describing two separate problems. Certainly, when cats have severe allergic responses, they can get respiratory problems so that would be a possible side-effect if a cat reacted badly to Convenia. Cardiomyopathy on the other hand, is probably not an immune mediated disease, especially the common form (hypertrophic). This can occur even in quite young cats and it does not have a known cause, so I would not think the antibiotic injection could be responsible.

  2. my cat aged 7 was injected with covenia without my consent and is now deaf also her quiet nature has changed. Will her hearing come back after 65 days, I fear your answer.

    1. Hi Frank. As much as I’m sad it was done without your consent, Convenia is an unlikely reason for a cat to go deaf. Therefore I can’t predict what might happen next but it would be worth talking to your vets about what else might be causing it.

  3. I lost my cat I strongly believe to Convenia after reading many reports from other cat owners who lost their cats. I wasn’t informed she was given this antibiotic after the vet came to talk to me after the evaluation. The vet suspected a UTI without completing an urinalysis She was never Ill never had an antibiotic she was 9 years old. After reading your article I believe this is what caused her death. I also wasn’t asked if she was hard to pill either

  4. Thank you for writing this article. I am struggling with finding a vet who dies not recommend it. I started going to a new practice. The first vet at this practice didn’t talk about Convenia.

    The second one recommended a second round and said that even though i don’t like Convenia, it would be better for a respiratory infection. I said no thank you.

    The previous practice injected my cat with it without my permission during a dental. Even though i said i don’t want it and the plan fir the dental clearly specified a different anti-biotic

  5. I’m furious with my local vet whom told me she was going to give my kitten an antibiotic injection for an infected spay wound. I assumed it was just the first shot that would be followed by oral antibiotics. However she told me afterwards that the injection lasts two weeks, so I can only assume it was convenia. I would never have agreed to my kitten having such a large dose of long acting drug injected into her body had I known. Surely this isn’t informed consent?! My kitten is much sleepier and more subdued than usual and not eating as much.
    After reading your post I’m even more upset that she’s had a 3rd line antibiotic. Where’s the accountability…thank you for your enlightening account.

  6. Thanks Andrew! I’m so excited to see you talk about antimicrobial resistance on this platform. As you said, it’s not just a human issue, it’s a global threat and we all need to do our part to use antimicrobials wisely.
    We get our new puppy in 4 weeks so I’ve been looking for a vet and came across your amazing blog. Needless to say I’ve booked her in at your clinic and for puppy school.

  7. thank you for writing fearlessly and frankly – antibiotic resistance is a huge issue for humans and everything you said re Convenia (the name sounds like a spoof!) could apply to how we use antibiotics. we’re all guilty of wanting convenience and silver bullets. i’m a new pet owner and in all the sea of opinion and advice your blog is refreshingly honest. thank you!

  8. I would be very interested in your views, or if you have ever written an article on the use of Gabapentin in dogs.

Leave a Reply

Your email address will not be published.