CSI Ballina: Kittens Under the Influence

Here’s a brief account of two kittens recently adopted-out by a welfare agency.  A few hours after arrival at their new home, one was lapsing into unconsciousness, the other was drunk and having trouble staying upright. The whole episode ended happily within 12 hours, but neurointoxication due to a usually safe worming treatment remains the only plausible explanation.


Two, healthy, six-week-old kittens were given a Milbemax® worming tablet in preparation for relocation to their new home. This treatment is recommended for kittens 6 weeks or older, weighing 0 – 2kg. They recieved no vaccination, anaesthesia, medication or insecticide in the days prior.

Both were playful and healthy when they left the welfare carer but within hours there was definitely something wrong. One became quiet, then groggy. So groggy, in fact, she lapsed into a deep sleep, from which she couldn’t be roused. The other remained conscious, but was drunk and wobbly when walked.

On vet examination, both were exhibiting neurological signs. One had ataxia alone, but perfomed well on neuro tests. The other was in state of profound somnolence – not unconscious, as she was responsive to stimulii. There where none of the parasympathetic signs typical of animals suffering pesticide overdose (muscle twitching, tremor, salivation).

All other bodily systems seemed unaffected: heart, perfusion and pulse indicated normal cardiorespiratory function;  normal temperatures didnt point towards immunologic stimulation of infection. There were no gastrointestinal symptoms, and the brighter one was still keen to eat.


While there’s a variety of brain disorders that can affect young kittens (congenital diseases, toxoplasmosis, hypoglycaemia), it seemed very unlikley 2 cats would develop these conditions, simultanously, without any other body systems affected. In summary, this presentation screamed ‘neurointoxication’.

The comatose kitty was ambulanced to vet’s house to spend the night. Placed on IV fluids and  heat mat to maintain body temperature and hydration, no other treatment was given. Within 12 hours, both kittens were back to normal and reunited. They continue to thive as adolescents.

Milbemycin is generally a safe and reliable worming agent that I continue to use in both my feline and canine patients, although events like this can shake a clinician’s confidence. Semi-anaesthetising one’s cat, when only intending to worm, is a fairly alarming side effect to a pet owner, however, from a medical point-of-view these kittens weren’t in any real mortal danger.

Similar neurological symptoms have been reported in dogs, but only when given a dose hundreds of times greater than that given to these kittens.   There have  been a small number of similar feline cases reported in online vet noticeboards, but this adverse reaction certainly isn’t common.

It’s possible these kittens received an adult size Milbemax® pill, inadvertently, or they may share a genetic sensitivity to this drug. One to avoid in the future, unless looking to sedate.



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7 Responses to “CSI Ballina: Kittens Under the Influence”

  1. Rhys Erskine says:

    Hi Matt,

    I had a very similar kitty about six months ago. In that case the owner had administered an entire adult tablet (ie enough for 8kg cat) to a six week old. Similarly, the kitten was fine the next day. I’m at home atm but i’m sure it says on the box (of twenty tabs) not to give to kittens <12wks. Of course, owners tend to purchase individual tablets, not boxes 🙁

  2. matt says:

    hey rhys, the emails are roling in…. now 2 other vets have emailed they’ve seen the same thing, one in combination with Revolution. Hopefully all this gets back to Novartis through APVMA.

    Agreed, the packaging is confusing and as confident the carer was when questioned, it would be an easy mistake for anyone to make.

    My tech specs say 6w.


  3. Lesa Corrine says:

    Interesting Matt..At Pets for Life Shelter..I use drontal and have not experienced what you have encountered.


  4. VOS says:

    Dear Little Kitties!
    Could be one big animal testing station with Pharmaceuticals!

  5. Nicoletta says:

    Matt.. you are a legend…. I really appreciate these posts.

  6. Dan says:

    Thanks heaps. We are currently having the same experience with our kitten. Very helpful in diagnosis.

  7. Alex C says:

    Hi, today I dosed my 5 adult cats with Milbemax for the first time, two of them (brothers) appear to be having the same side effects as the 2 kittens described above. They are both large cats and over two years old. One appears to have gastro-intenstinal stress, was acting as if ‘drunk’ or drugged, rapid breathing, unable to stand properly and has now fallen into a deep sleep. The other has similar symptoms, but less pronounced. Both are fairly large cats, 4kg and 5kg and were given 1 adult tablet each. The other three cats dosed at the same time (one of which is a brother to the two affected) are behaving normally and showing no side effects.

    From the above and through other comment sites I have noted that this is rather more common than might be realised. I found no mention of this rather scarey problem on the ‘side effects/ precautions’ portion of the leaflet with the tablets. I would hope that this gets looked into by the manufacturers, particularly as it is so unexpected and I assume likely to be misdiagnosed as a severe neurological problem likely to attract treatment that may exacerbate the problem.

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