Nonsteroidal anti-inﬂammatory drugs in the cat
The recognition of pain in the cat is difﬁcult when compared to other species of domestic animals and humans. Acute pain is probably easier to recognise than chronic pain in the cat. Animals in acute pain will often remain quiet andimmobile and have a tense appearance. Occasionally they may become aggressive and resent handling. Vocalisation is relatively rare apart from the occasional growl although this may to some extent be related to the breed of cat. In fact, they may even continue to purr. During recovery from major surgery cats may demonstrate a manic reaction on emergence from anaesthesia which may be difﬁcult todifferentiate from an acute pain response. If acute limb pain is severe they may attack a dressing or even attempt to discard it. This behaviour may be accompanied by considerable vocalisation. After abdominal surgery, cats which are in pain may adopt sternal recumbent position and tense their abdominal muscles. If post-operative pain is present in the facial region cats may attempt to rub or scratch theaffected area which may compromise a successful outcome to the procedure (Flecknell and Waterman-Pearson 2000). Chronic pain is often associated with a number of conditions including neoplasia, oral disease, wounds and dermatitis in addition to osteoarthritis and degenerative joint disease. The incidence of these latter conditions has probably been underestimated in cats (Clarke et al. 2005). Thebehavioural changes associated with these conditions may be insidious in onset and easily missed and are often attributed by the owner to the ‘ageing process’. Lameness or exercise intolerance are not common complaints by owners. There may well be behavioural changes which can generally be classiﬁed as a reduced ability to ‘care for themselves’ and an inability or reluctance to jump, particularlyup onto or down from surfaces. It may well be that these changes are so subtle that they are not appreciated by owners until they observe the obvious improvement after appropriate analgesic therapy (Robertson 2006).
The use of nonsteroidal anti-inﬂammatory drugs (NSAIDs) in cats is the subject of a review in this issue of the journal (Lascelles et al. 2007). These drugs are a group of weakorganic acids, carboxylic acids (aspirin, carprofen) and enolic acids (meloxicam, phenylbutazone). Their main therapeutic effects of reduction of fever, pain and inﬂammation are due to their inhibition of prostaglandin production from arachidonic acid by the cyclooxygenase (COX) enzymes. There are two distinct forms - COX-1 and COX-2. COX-1 is involved in the regulation of gastrointestinal and renalblood ﬂow and has a role in blood clotting. In contrast, COX-2 is an inducible enzyme which is expressed at the sites of inﬂammation in response to inﬂammatory mediators. Earlier published work had indicated that the prostaglandins that mediate inﬂammation were produced by COX-2 whereas those that were important in gastrointestinal and renal function were produced via COX-1. This gave rise to thebelief that NSAIDs exerted their useful therapeutic effects by COX-2 inhibition, whilst the inhibition of COX-1 was considered to be responsible for some of the toxic side-effects. It is now clear that this was very much an oversimpliﬁcation and that the whole subject is more complex and species differences may also be important. Most NSAIDs are metabolised in the liver and excreted via the bileduct or kidneys. As the cat has a reduced ability for glucuronidation of drugs then it follows that agents (aspirin, carprofen) which are metabolised by this route will have a longer drug elimination half-life in this species than in the dog. In contrast, drugs (meloxicam) which are cleared by oxidative enzymes have a similar or reduced halflife in cats when compared to dogs. A number of adverse...