The first case I used ketamine 0.5 mg/kg SQ on was a dog with lumbosacral degeneration, back in 2012. This poor dog was intolerant of a fair number of chronic pain meds and fortunately was owned by a receptionist of the local veterinary behaviourist. We started once monthly with ketamine 0.5 mg/kg SQ and he improved. He carried on like this for around 2 years but as his pain progressed, we increased the frequency of administration – right up to q48hrs in a palliative manner in his final days.
The exact mechanism by which ketamine provides analgesia is likely to be via action at the NMDA receptors. These receptors are upregulated in chronic pain and play a key role in central sensitisation. It is therefore suggested that ketamine has an anti-hyperalgesic effect in patients suffering from central sensitisation. This could explain why ketamine is effective in some patients but not in others.
We have little evidence beyond such anecdote and it’s important to be clear on that. In chronic pain we do have some great options with an evidence base, albeit limited (such as amantadine) – but also a lot of what we do is trial and error. In this webinar I have reviewed what we know about the use of ketamine in chronic pain in people. Click here and scroll to find Subcutaneous ketamine for chronic pain.
Often before the clinical trials come the anecdote – and that is where we are with ketamine SQ. A clinical trial is of course on my to-do list and is discussed in the webinar.
Do I see side effects?
Very rarely. The dose is so low (0.5 mg/kg = analgesia versus 3-5 mg/kg = anaesthesia) and so we don't expect to see any of the effects we are familiar with from ketamine anaesthesia. I discuss this with owners and say that it would be very rare. Most owners report that the dog sleeps well after the injection.
Same dose in dogs & cats?
Yes. To start with. Any initial work should look at dose ranging studies to determine optimal dosing in each species. Until we build an evidence base we use 0.5mg/kg.
Can I use in cases with heart disease?
Yes. Again, it’s dose related so such a low dose will have minimal (zero) effect on cardiac myocytes.
How does it work?
The million dollar question. We know ketamine acts on NMDA receptors as a predominant analgesic mechanism but there could be other effects.
How long does it last for?
In my experience this is very individual and this is a discussion to have with owners. In mild pain cases I suggest starting with monthly intervals. In severe pain I would recommend the owners come back for an assessment one week later.
Can I use alongside X drug?
Again anecdote. I have used ketamine alongside a whole host of analgesics. I do use ketamine in dogs already receiving other NMDA antagonists (amantadine, memantine) and have never seen adverse effects from this.
What about a CRI?
I use ketamine continuous rate infusions for pain breakthrough where admission to hospital is required. An example would be a septic arthritis in an OA patient. Ketamine as a CRI is reviewed here and will be discussed extensively in our CRI masterclass webinar.
Ketamine SQ is an option that I recommend for improving pain control in cases with a pain management plan and for those suffering breakthrough pain. It’s a great option for bonding owners as it can only be administered by a veterinary surgeon, meaning those cases come back to you for regular assessment.
I look forward to hearing your experiences with this. Mine have been mostly positive and my experience is that 70-80% of dogs & cats respond well. For further detail, please watch our webinar.
This post was written by Matt Gurney in 2021 and updated March 2024.
Matt & Carl established Zero Pain Philosophy to provide educational resources to veterinary professionals enabling optimal management of pain.
Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Eastcott Referrals. Matt is Past President of the European College of Veterinary Anaesthesia & Analgesia.
Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is President of the Association of Veterinary Anaesthetists. Carl works at Anderson Moores Veterinary Specialists.