Subcutaneous ketamine for analgesia

Now there’s a story here! Several years ago I had a few practitioners contact me to ask about using ketamine subcutaneously (SQ) as an analgesic in chronic pain. They told me a surgeon had told them to call me about it because I was using in my practice! At this stage I wasn’t using ketamine SQ and was puzzled who this surgeon was. It turns out it was Turlough O’Neill who had taught me orthopaedics at Liverpool Uni and who I then went on to work with at Northwest Vet Specialists.

The first case I used ketamine 0.5 mg/kg SQ on was a dog with lumbosacral degeneration. 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.

Why am I telling it like a story? 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 (such as amantadine) – but also a lot of what we do is trial and error. 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!

Do I see side effects?

Very rarely. The dose is so low (0.5 mg/kg = analgesia versus 3-5 mg/kg = anaesthesia). I discuss this with owners and say that it would be very rare. Most 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.

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 all been positive so far.

This post was written by Matt Gurney.

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 Anderson Moores Veterinary Specialists. Matt is 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.