MANAGEMENT of existing pain in cats is often a challenge. This is due to the smaller range of analgesic agents licensed for use in cats and the smaller amount of information available, never mind evidence of effectiveness. Difficulty in getting cats to take medication in food also poses a problem for longer-term analgesia.
There is a reluctance to use many medical agents in older cats who are suffering from chronically painful conditions for fear of toxicity, especially if there is existing intercurrent disease. However, actually identifying that a cat is suffering from sub-acute or chronic pain is probably the greatest challenge to providing appropriate analgesia.
Existing pain
Situations where cats may be experiencing pain are wide and varied. They can be grouped by cause and by expectation of duration. The first is directly related to the other if the pain is a result of a disease process that can be eliminated or cured so that the source of pain is removed.
In diseases that are lifelong or chronic in nature, the source of pain cannot be eliminated, producing a scenario where constant palliation is the target. Differentiation must be made between each of these broad entities, as expectation of success and rationale of management will vary depending on the cause.
Situations where analgesic management is needed include:
- post-operative recovery period,
- inflammatory or infectious painful conditions,
- non-surgical trauma,
- chronic painful disease.
Recognising pain
Developing an understanding of the particular way cats, as a species, respond to pain determines our challenge in identifying and modifying it. Few would argue the fact that analgesia should be provided when a cat is in pain; the dilemma is more about recognising this fact.
This dilemma is made worse by the fact that many species, including cats, may hide pain as a natural protective mechanism. This does not assist the clinical observer trying to identify the animal in pain.
It has become clear that altered behaviour is a key indicator and is much more reliable than physiologic measurements in making a judgement of both presence and severity of pain. However, this requires a good understanding of what normal behaviour is, particularly of the individual concerned. For this reason, owners, or others caring for a hospitalised pet are much better placed to identify signs of pain as they typically spend more time observing the cat.
Cats are far less demonstrative of pain as a species than dogs. Their typical response when in pain is to withdraw and hide, shunning any attention. This makes the identification of any outward physical signs extremely difficult.
In situations where severe pain is present, signs such as overt aggression, hyperventilation, vocalisation and frantic physical activity such as rolling or tearing at IV lines and wound dressings can be observed. However, the withdrawal scenario is much more common with the cat hiding hunched in the back of a hospital or carrier cage (Figure 1), reluctant to move and unresponsive to any physical attention.
Any attention may be met by vocalisation and aggression and this may also occur if attempts are made to move the cat. Other signs associated with pain include crouched, hunched position with head held low, squinted eyes; reduced palpebral apertures and attempts to hide or escape (Robertson, 2008).
Attempts have been made to further qualify the signs to give a more specific set of descriptions (Mathews, 2000), recognising alterations in a number of different areas; vocalisation; facial expression; self-awareness; locomotion; activity; attitude; appetite; urination and bowel movements; grooming; response to palpation and posture of the cat.
Interaction with the cat by the caregiver is one way of trying to assess some of the key behavioural signs. Identification of normal behaviour signs such as grooming and using litter tray normally are reassuring when trying to assess whether pain is present or not.
In many cases, a good way of confirming the presence of pain is to administer a test dose of analgesic and observe a positive response.
Chronic or persistent pain
Chronic pain is the focus of a great deal of attention affecting well-being in dogs affected with chronic diseases like osteoarthritis and cancer. Osteoarthritis was not commonly identified as a cause of significant clinical problems in the cat until relatively recently with the exception of inflammatory joint disease seen in young cats (Robertson, 2008; Lascelles, 2010; Slingerland et al, 2011; Bennett et al, 2012a).
When radiographic evidence of osteoarthritis is recognised in affected animals it is often dismissed as clinically insignificant (Figure 2). New interest and information has resulted in a reappraisal of both the prevalence and importance of this problem in the cat. This interest is due in part to identification of a very high incidence of radiographic and pathological changes in the older cat population (Hardie et al, 2002; Godfrey, 2005; Clarke et al, 2005) (Table 1).
Pain management strategies
Cats clearly require pain management in the short to medium term for many painful conditions and over much longer periods in the painful chronic diseases (Hellyer et al, 2007). Failure to provide analgesia in many cases is the result of poor identification of pain itself or of fear of using pharmaceutical intervention.
Toxicity or adverse effects
Much of current veterinary knowledge about drug side-effects and toxicity is derived from canine studies. The species jump to the cats with their peculiar metabolism often deters vets using analgesics for fear of producing toxicity or adverse effects.
Certainly, cats have a low capacity to handle drugs that require hepatic glucoronidation (Robertson, 2008). This has produced problems using certain NSAIDs in cats. The feline susceptibility to toxicity when using phenolic drugs such as paracetemol and the long half-lives of some drugs like aspirin and carprofen is widely publicised and demands a cautious approach. But there are newer safer agents available licensed for use in cats that can provide the necessary analgesia whilst eliminating most of the risk.
Meloxicam is eliminated by oxidative enzyme clearance while ketoprofen, which should have a long half-life as it is eliminated by glucoronidation in the dog, does not in the cat, suggesting an alternate path of elimination. Robenacoxib is cleared very rapidly from the main tissue compartments reducing the risk of toxicity but is concentrated at the site of inflammation due to tissue selectivity (King et al, 2011).
Suggested strategies for short to medium term analgesic management
Many conditions require immediate pain control, which can be easily continued for a number of days. In these conditions, either a resolution of the inciting cause is removed or the condition is improved to a stage where analgesia is no longer required.
Such indications may include the post-operative recovery period after many surgical procedures, following either musculoskeletal or soft tissue trauma, cat bite abscess, dental disease or exacerbation of existing osteoarthritis.
Mathews (2000) has attempted to provide an indication of suitable pharmacological intervention by using a scale of anticipated level of pain for a list of common conditions. For conditions expected to produce moderate to severe pain, opioids may be indicated initially. Morphine at 0.1-0.5mg/kg either IM or SC would produce good pain relief for 2-6 hours. Buprenorphine can also be used by IM route at 0.01mg/kg to give variable duration analgesia of between 4-12 hours. Buprenorphine can also be delivered trans-mucosally via the mouth. This is useful as it avoids the problems of repeat injections. Tramadol has also been reported to be effective in cats given orally at a dose of 3mg/kg every 12 hours.
The pharmacokinetics are more consistent than in the dog with rapid absorbtion and a long half-life leading to a potentially more reliable analgesia. Dysphoria is a common side-effect in cats. Tramadol is also a useful adjunctive agent used with NSAIDs but is not licensed in cats.
Alternatively, NSAID agents can be used to provide analgesia over the same period (Table 2). The agents listed – meloxicam, robenacoxib, ketoprofen and tolfenamic acid – are all licensed for short-term use in cats. These are more convenient to use, especially in animals being sent home from the hospital, and are able to deliver a satisfactory level of analgesia (Lascelles et al, 2001; Gunew et al, 2008; Giraudel et al, 2010).
They offer greater convenience when used due to no regulatory requirements and are flexible with injectable preparations and palatable oral forms for easier dosing (liquid meloxicam; flavoured tablets; robenacoxib). Greater confidence in using these analgesics is improving pain management over the short term in cats. Care must be exercised when using NSAIDs in any species and this is also true in the cat (Sparkes et al, 2010).
Strategies for management of chronic disease (osteoarthritis)
Management of the disease presents a genuine challenge. In the majority of cases the clinical presentation is that of chronic osteoarthritis requiring longterm analgesia. There is less experience and information about the safety of using NSAIDs, the first line analgesic in most other species, in the cat, although this is increasing. Sparkes and others (2010) produced an excellent review article on the long-term use of NSAIDs.
Many of the products licensed for use in cats are only for short-term use and this is unlikely to change in the current financial climate. The current exception is meloxicam, which has a long-term licence in the EU. Shortterm treatments within licensed periods may be effective in improving clinical signs especially if there are clinical exacerbations.
We still do not fully understand the relationship between the pathological disease and the likelihood of painful consequences in cats and shortterm management may be effective combined with other measures in a multimodal treatment plan. However, these agents can be used with care if clinical need dictates this on a more long-term basis as identified in the article (Sparkes et al, 2010) and the patient is unresponsive to other treatments. Longer term licensing would certainly open up better options for management.
Screening for pre-existing disease is important as is regular monitoring to avoid unnecessary problems and allow informed treatment. The high incidence of chronic kidney disease and hyperthyroidism in older cats makes it highly advisable to check blood pressure and test urine and blood samples before deciding on treatment. Risks can be quantified and reduced dose or dose interval for suitable NSAIDs can be employed allowing the necessary analgesia to be delivered safely.
Adoption of a multimodal approach, as in the dog, is to be encouraged. Using this, other measures such as adjunctive analgesics and therapeutic diets containing EPA and DHA may be used to reduce the necessary dose of NSAID. There are still some questions as to whether these diets are as effective in cats as in dogs (Lascelles, 2010; Bennett et al, 2012b).
Obesity avoidance and control is extremely important. Using nutraceuticals like glucosamine and chondroitin sulphate in cats is widely practised as a safe and effective option. This is questionable as there is still no real convincing evidence of benefit with these agents and they certainly should not be used as the only agent if a cat is perceived to be in pain.
Exercise or activity management is much more difficult to modify in the cat. However, environmental modification where the cat is having difficulty can be important.
Simple measures such as avoiding feeding the cat on a high table or even using low-sided litter trays can make a big difference if problems are being experienced in these areas.
Rehabilitation and physiotherapy as options in cats are in their infancy as therapeutic methods but are well tolerated (Figure 3) and are likely to become much more popular. The same can be said for acupuncture in cats.
Key to establishing the effectiveness of any of these management measures is a set of outcomes, which can be evaluated and compared. An interesting new development in this area is the development of a clientbased questionnaire (Zamprogno et al, 2010). This has exciting implications for the future.
Summary
The key to effective management of pain in cats is improved awareness and skill in identification of the signs of pain and discomfort.
This has to be combined with increased confidence in using pharmacological intervention more confidently and more effectively and combining this with nonpharmacological measures.
Chronic disease management still poses real challenges for pain control but the emergence of tools which may be able to improve identification of pain and measure improvement holds great hope for the future.
References
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