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Paracetamol is one of the most commonly-used drugs worldwide. It is available to buy over the counter for humans, and for dogs (as Pardale-V tablets, an NFA-VPS medicine). This module summarises the evidence on the use of paracetamol in dogs. It is important to note that paracetamol should never be used in cats.
By doing this module you will:
be aware of current knowledge about how paracetamol works
know the contents and licensed use of Pardale-V tablets for dogs
be aware of the amount of clinical research knowledge on paracetamol in dogs
know the adverse effects of paracetamol, and the dangers of overdose.
know what to say to clients about the use of paracetamol in dogs
Paracetamol has pain-relieving (analgesic) and temperature-lowering (antipyretic) effects. It has no significant anti-inflammatory effect.
There has been some debate about whether or not paracetamol should be regarded as being in the same class of drugs as non-steroidal anti-inflammatory drugs (NSAIDs), such as carprofen and meloxicam. This may be because paracetamol was thought to have a similar mode of action to NSAIDs (which are known to inhibit the enzyme cyclooxygenase (COX), which is involved in the production of inflammatory prostaglandins). However it is now widely agreed that paracetamol is not an NSAID, although it might have some similar actions (that is analgesic and antipyretic effects) and some similar adverse effects. In the World Health Organization classification of veterinary medicines, paracetamol is in a different class from NSAIDs. It is grouped with ‘Other analgesics and antipyretics’
Exactly how paracetamol works is not known. It may have several modes of action including inhibition of prostaglandin synthesis in central nervous system tissues; effects on a subtype of the COX enzyme; and effects on cannabinoid (CB1) receptors.
After giving paracetamol by mouth to dogs, it is rapidly absorbed from the gastrointestinal tract, but the presence of food in the stomach slows down the absorption. Paracetamol given rectally to dogs is poorly absorbed.
In dogs paracetamol is broken down to non-toxic metabolites which are excreted in the bile and urine. It is broken down fairly quickly (it has a short half-life, ranging from around 1 to 3.5 hours). However in paracetamol overdose in dogs (or humans), the normal breakdown pathways (glucuronidation and sulphation) become saturated and a different breakdown pathway (oxidation) takes over leading to the production of toxic metabolites, which can cause liver damage and other toxic effects. Cats are particularly sensitive to paracetamol because their capacity for glucuronidation and sulphation is low and so paracetamol in cats is more likely to be broken down by oxidation resulting in the production of toxic metabolites. This is why paracetamol must never be given to cats.
In the UK, one paracetamol product is authorised for use in dogs: Pardale-V tablets. This product has been available for many years as a NFA-VPS medicine, and so it can be sold without a prescription by a vet, pharmacist or SQP. Each Pardale-V tablet contains paracetamol (400 mg) plus codeine, an opioid analgesic (9 mg). Pardale-V is an authorised veterinary medicine. It is authorised for up to 5 days’ use “for the treatment of acute pain of traumatic origin, and as a complementary treatment in pain associated with other conditions and post-operative analgesia”. Use of Pardale-V for longer than 5 days is unlicensed and so must be prescribed by a vet. Codeine is poorly absorbed in dogs and so the codeine content of Pardale-V is not thought to contribute any pain-relieving effect.
Paracetamol also has a veterinary marketing authorisation for use in pigs, for symptomatic treatment of fever, in the form of a solution for drinking water and as a feed pre-mix (under the brand names Piretamol, Pracetam). These are only available on veterinary prescription (POM-V) and are not suitable for administering to dogs.
Paracetamol formulated for humans may be prescribed by a vet via the prescribing ‘cascade’ if the veterinary formulations are deemed unsuitable. Human paracetamol is available orally (as tablets, capsules and syrup), as suppositories, and as a solution for intravenous (IV) injection. Many human oral preparations contain paracetamol in combination with other drugs such as opioids, aspirin, ibuprofen, antihistamines, decongestants and caffeine and it is important to avoid giving these combinations to dogs.
We found only four published trials assessing paracetamol in the management of acute pain in dogs.
Two of the studies (which were randomised, blinded, placebo-controlled and crossover in design) were performed in the late 1980s/early 1990s (Mburu et al 1988; 1991). They involved assessing the effects of paracetamol by mouth in a small number of dogs that had undergone experimental orthopaedic limb surgery. The results suggest that oral paracetamol used at a dose of 27mg/kg every 8 hours significantly reduced post-operative pain but that a lower dose of 10mg/kg every 8 hours did not. However the researchers used crude measurements and so the results may not be reliable.
In a another study, six healthy greyhounds were given paracetamol by mouth (at a dosage of 14–23 mg/kg) plus codeine (1.6–2.5 mg/kg) (KuKanich 2016). No pain-relieving effects were detected. However, the method used (an electronic device that applies mechanical pressure) may not be a reliable method of assessment.
Finally, in a randomised, blinded, clinical trial, 48 dogs undergoing tibial plateau levelling osteotomy (TPLO) surgery were given either paracetamol plus hydrocodone (an opioid) (at a dose of 16.6 mg/kg paracetamol, 0.51 mg/kg hydrocodone) or tramadol (5.85 mg/kg), by mouth every 8 hours after surgery. (Benitez et al 2005) Overall, 29% of dogs required rescue analgesia after the second dose but there were no significant differences between groups. The trial’s authors concluded that neither paracetamol plus hydrocodone nor tramadol was acceptable for clinical management of orthopaedic post-operative pain.
In summary, the use of paracetamol for acute pain-relief in dogs has not been well studied.
To our knowledge, there are no published studies assessing paracetamol in the treatment of chronic pain in dogs. Anecdotal evidence on long-term use of paracetamol comes from veterinary surgeons’ experience of dog owners reporting behavioural signs of improved comfort.
The summary of product characteristics (SPC) for Pardale-V lists no adverse effects for paracetamol but states that occasional constipation may occur due to the codeine content.
In the papers used to write this module, reported adverse effects of using paracetamol alone or in combination with codeine have included vomiting, sedation, panting, drooling and regurgitation
To our knowledge, the long-term use of paracetamol in dogs has not been studied and so the potential adverse or toxic effects from long-term use are not known. Even though paracetamol has been around for a long time it is still important to report suspected adverse effects to the Veterinary Medicines Directorate.
Paracetamol toxicity due to administration of human products to animals by their owners or accidental ingestion is reported frequently with clinical signs ranging from sedation alone to severe signs, including low body temperature, rapid breathing and heartbeat, facial swelling, vomiting and diarrhoea progressing to jaundice, convulsions and death. Cats are especially prone to serious toxicity which is why paracetamol should never be used in cats.
For managing acute pain, the licensed dose of paracetamol in Pardale-V is one tablet per 12kg bodyweight (which is equivalent to 33.3 mg/kg) every 8 hours. This is higher than the dosage recommended in the British Small Animal Veterinary Association (BSAVA) Small Animal Formulary (10 mg/kg every 12 hours). However, the licensed dose is more in keeping with the limited clinical trial evidence (in acute pain following orthopaedic surgery) described earlier.
There is no published evidence of the efficacy of intravenous paracetamol when used during surgery. This use of paracetamol is not licensed and may only be prescribed by a vet under the ‘cascade’.
For managing chronic pain there is no evidence to guide paracetamol dosage. Use of paracetamol for more than 5 days is unlicensed and can only be prescribed by a vet under the ‘cascade’. For long-term use, the vet must seek informed client consent based on a discussion about the balance of risk (i.e. undefined long-term effects of paracetamol) versus benefit (i.e. patient comfort).
Interest in a multi-modal approach to managing acute and chronic pain may be increasing the veterinary use of paracetamol. In theory, paracetamol might add to the analgesic effect of other pain-relieving medicines, such as NSAIDs because of having a different mode of action. In humans, paracetamol is routinely used alongside ibuprofen (and other NSAIDs). However, the use of paracetamol in conjunction with NSAIDs has not been evaluated in dogs. Nevertheless, a vet might decide to prescribe it with an NSAID or other analgesic for chronic pain that is not adequately managed with NSAIDs, or when NSAIDs are unsuitable. When combining paracetamol with other analgesic drugs, the prescribing vet must take into account the possible adverse effects of the other medications (e.g. effects on the kidneys or liver) to make an informed decision. Use of paracetamol alongside another drug (such as an NSAID or a steroid) is a calculated risk, like many other decisions about treatment made regularly by vets.
Paracetamol should not be used in animals with severe liver or kidney impairment; or in animals that are dehydrated because adverse effects may be more likely. (Note that the summary of product characteristics (SPC) for Pardale-V includes the standard contraindications for NSAIDs: animals with heart, liver or kidney disease or in animals in which there is a possibility of gastrointestinal ulcer or bleeding, or evidence of a blood dyscrasia or hypersensitivity).
Paracetamol must never be used in cats because of the potential for fatal toxicity.
When used at recommended doses for short-term pain control in otherwise healthy patients, little monitoring should be necessary. However, if used for long-term therapy (which is an unlicensed use), the effects of paracetamol must be assessed frequently. Regular pain assessment may take the form of a simple daily diary (examples can be found on the Canine Arthritis Management (CAM) website) or an established pain assessment tool such as the Canine Brief Pain Inventory, validated for osteoarthritis or the VetMetrica quality-of-life assessment tool. Long-term monitoring for adverse effects includes checking liver and kidney functions and asking the owner to report any adverse effects.
Paracetamol may be useful for treating both acute and chronic pain in dogs. There is only one product containing paracetamol that is licensed for use in dogs. It is Pardale-V, which can be sold without a prescription or it may be prescribed by a vet. Pardale-V contains paracetamol plus codeine. The licence for Pardale-V is specifically for use to treat acute pain for up to 5 days.
A vet might decide to prescribe Pardale-V for longer than 5 days to help manage more long-term pain. If the combination of paracetamol and codeine in Pardale-V is not considered suitable for a dog, the vet might prescribe a human paracetamol product. When prescribing Pardale-V or human paracetamol in this way (i.e. outside the terms of the product licence), the vet will normally ask the dog owner to give their consent.
Paracetamol is unikely to cause any adverse effects in dogs, although the codeine in Pardale-V might cause constipation or panting. If paracetamol has been prescribed for the long-term management of pain, the vet may have given instructions for monitoring the effects on pain. Future blood tests might be needed to monitor kidney and liver function. The client should report if they notice any side effects they think might be due to the treatment. Remind owners to give only the prescribed dose at the frequency instructed and not to give extra if the dog seems more uncomfortable, but to seek veterinary advice.
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How we produced this module
A more detailed version of this module is published on www.veterinaryprescriber.org .Our modules start with a detailed outline and electronic literature search. We commission a collaborating author to write the first draft of the text. The collaborating author on this module was Gwen Covey-Crump, RCVS Recognised Specialist in Veterinary Anaesthesia, EBVS European Specialist in Veterinary Anaesthesia and Analgesia, President, Comparative Medicine Network, Royal Society of Medicine. The draft is circulated unsigned to a wide range of commentators, including practising first-opinion vets, topic specialists, the companies that market any mentioned drugs and other organisations and individuals, as appropriate. They can raise points about the interpretation of evidence, ask questions that are important to clinical practice, and present alternative viewpoints. There is a rigorous editing and checking process and the result is a module that is evidence-based, impartial and relevant to clinical practice. The final module is unsigned because it is the result of collaboration.
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