Methadone plus Ketamine - redundant?

RE: Methadone plus Ketamine - redundant?

Andrea Tarr — Mon, 06 May 2019 12:04:43 GMT

Veterinary Prescriber recently published a critical review of the use of paracetamol in dogs, based on a thorough search of the published literature. Here's what was found on iv use:

"For IV use of paracetamol (which is an unlicensed use), both the WSAVA guidelines and BSAVA Formulary recommend a dosage of 10mg/kg every 8 to 12 hours (Matthews et al. 2014; Ramsey 2017). One pharmacokinetic study detected no adverse effects when paracetamol was administered IV to 20 dogs at a dose of 10 mg/kg or 20 mg/kg (Serrano-Rodríguez et al. 2018). IV paracetamol may provide peri-operative pain relief alongside analgesics such as opioids when NSAIDs are contraindicated. However there is no published evidence of the efficacy of paracetamol when used during surgery."

Serrano-Rodríguez JM et al. Comparative pharmacokinetics and a clinical laboratory evaluation of intravenous acetaminophen in Beagle and Galgo Espaol dogs. Vet Anaesth Analg 2018 [Accepted Manuscript].

https://www.veterinaryprescriber.org/subscribers-content/paracetamol-for-the-management-of-pain-in-dogs

RE: Methadone plus Ketamine - redundant?

Jo Murrell — Mon, 06 May 2019 11:37:47 GMT

Good point! i also don't know where the dose of 10 mg/kg comes from - and we need some more research to back up what would be the optimal dose of paracetamol (analgesia versus side effects).

RE: Methadone plus Ketamine - redundant?

Michael Woodhouse — Sun, 05 May 2019 17:54:47 GMT

[quote user="Jo Murrell"]injectable paracetamol at 10 mg/kg IV may be a suitable alternative.[/quote]

Hi, Jo. Do you know where this dose comes from? It's been in BSAVA formulary forever but I can't find any sort of reference to back that up. What we do have is Pardale V licensed with a dose rate of 33.3mg/kg. In human medicine they use the same maximum dose per day when given orally or IV (4g).

I've used a lot of Pardale V alongside NSAIDs and other drugs long term with good results. Whilst I use Pardale at the licensed dose rate I do get an off license form for use longer than 5 days and concurrently with NSAIDS. I've had dogs on this for years with no problems with liver etc.

In the last few years we've used some IV paracetamol to add to the analgesia or when NSAIDs unsuitable. We've used 10mg/kg but it doesn't make any sense and I can't find any sort of reference where the dose came from. It just feels like a very convenient dose rate rather than one derived in a scientific way.

Any thoughts?

RE: Methadone plus Ketamine - redundant?

Jo Murrell — Sun, 05 May 2019 08:56:05 GMT

In the QUAD protocol the ketamine adds in the anaesthesia so although you may get some cross over in terms of the mechanism of analgesia with the methadone it is essential. Although you could argue that we used iso - so that the ketamine could have been replaced by the iso so that we would then be using medetomidine, midazolam, methadone as a normal premed - but we would probably have needed a higher concentration of iso in this case.

I think when patients pant it is really difficult to know if there is a component of pain or whether it is drug induced - using the GCPS-Canine can help as panting is not one of the categories so if they score highly on the pain score you can be more certain that it is pain related. I haven't had much experience giving medetomidine to dogs that are panting from methadone but it is definable worth a try as the medetomidine should settle them down.

I have given animals 0.3 mg/kg methadone and then another 0.3 mg/kg so above the 0.5 mg/kg limit - but if thats still not successful then i usually look to other alternatives. In my experience a fentanyl CRI is fairly reliable and will provide top up analgesia to methadone (1-5 mic/kg/hour) - but also consider NSAIDS or if they are contraindicated injectable paracetamol at 10 mg/kg IV may be a suitable alternative.