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in Table 2. Such CMIs are chronic pain indices that primarily utilize pet owner observations and input. Ideally, patients with chronic pain should be evaluated with one of the multifactorial CMIs. Pharmacological Intervention of Pain Effective pain management generally involves a balanced or multimodal strategy using several classes of pain-modifying medications.The rationale behind this approach is that it addresses targeting multiple sites in pain pathways, potentially allowing lower doses of each drug and minimizing the potential for side effects associated with any single drug. The choice of medication should be based on anticipated pain levels and individual patient needs. Anticipatory analgesia provided prior to pain onset is more effective than analgesia provided once pain has occurred, contributing to both a dose- and anesthetic-sparing effect. Opioids Opioids are the most effective drug class for managing acute pain and can play a role in managing chronic pain. An improved understanding of neuropharmacology and the development of novel formulations of opioids makes it incumbent on veterinarians to remain familiar with their modes of action; various subtypes within this drug class; and the prevention, recognition, and treatment of adverse effects. While a complete discussion of opioids is beyond the scope of these guidelines, the Task Force makes the following recommendations for using this class of drugs in dogs and cats: Opioids should be used as a routine preoperative medicant, preferentially in combination with a tranquilizer/sedative (e.g., acepromazine, midazolam, diazepam, or a-2 adrenergic agonist such as dexmedetomidine) when the patient’s condition warrants their use. Full l agonists elicit greater and more predictable analgesia than partial l agonists or j agonists. In dogs, the l antagonist/ j agonist butorphanol in particular appears to have limited somatic analgesia and very short duration of visceral analgesia.12,13 In a comparison study, buprenorphine administered before surgery and during wound closure provided adequate analgesia for 6 hr following ovariohysterectomy in cats, whereas butorphanol did not.14 In cats, the subcutaneous route of opioid administration is not recommended. IM and IV routes are preferred both pre- and postoperatively.15 The oral transmucosal or buccal route of administration for buprenorphine may also have clinical efficacy as well.16,17 The individual effect of any opioid, including duration, may vary widely from patient to patient. Postoperative reevaluation should be made frequently to determine ongoing opioid requirements. For a patient undergoing major surgery, whereby ongoing opioid administration can be anticipated, the clinician may choose from the following strategies: * Periodic readministration of parenteral opioids. * Constant or variable rate infusion. Calculators can be found online. * Long-acting formulations and technologies. For dogs there is an FDA- approved transdermal fentanyl producta . Given this canine fentanyl product on the market, the Task Force discourages the use of human commercial fentanyl patches in dogs due to highly variable pharmacokinetics, risk of either accidental or purposeful human exposure, with potential liability for extralabel use. There is not an expert consensus regarding the utility of fentanyl patches in cats. The FDA has more recently approved a concentrated injectable buprenorphine product for catsb , which has been formulated to provide a 24 hr duration of action when administered as directed. TABLE 2 Multifactorial Clinical Measurement Instruments (CMIs) for Chronic Pain Assessment in Veterinary Medicine Helsinki Chronic Pain Index (HCPI) Canine Brief Pain Inventory (CBPI) Cincinnati Orthopedic Disability Index (CODI) Health-Related Quality of Life (HRQL) Liverpool Osteoarthritis in Dogs (LOAD) Feline Musculoskeletal Pain Index (FMPI) JAAHA.ORG 71 Pain Management Guidelines for Dogs and Cats * Oral opioids. Dogs exhibit a robust first-pass effect of oral opioids. No clinical studies document efficacy, but pharmacokinetics of codeine and hydrocodone suggest possible utility.18 No comparable studies exist for cats. Opioids are synergistic with a-2 adrenergic agonists, allowing them to be used in low-dose combinations, either with or without ketamine, to great effect for both sedation and analgesia. Opioids play a significant role in human medicine for the treatment of chronic pain and may play an underappreciated role in dogs and cats as well, especially for cancer-related pain and in palliative care patients. That said, clinicians must be vigilant with regard to long-term adverse effects such as constipation, drug tolerance, and the potential for diversion by clients. Nonsteroidal Anti-Inflammatory Drugs The majority of conditions that cause pain have an inflammatory component. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a mainstay for management of chronic pain as well as for perioperative use. NSAIDs should be used for their central and peripheral effects in both dogs and cats after consideration of risk factors. There is no indication that any one of the veterinaryapproved NSAIDs are associated with any greater or lesser incidence or prevalence of adverse events (AEs).19 Canine and feline veterinary-approved NSAIDs have demonstrated acceptable safety profiles, which is in contrast to nonapproved NSAIDs such as aspirin, ibuprofen, naproxen, and meloxicam for human use.20–22 Long-term use of low-dose meloxicam is approved in cats in many countries other than the US. AEs related to NSAID use in dogs and cats can be minimized by appropriate use as outlined in Figure 3. Although the overall incidence and prevalence of NSAID-related toxicity is unknown, it does appear to be very low relative to the number of doses administered.20 Of the AEs associated with NSAIDs, gastrointestinal (GI) toxicity is the most common. The GI clinical signs associated with NSAID toxicity in dogs include vomiting, diarrhea, and inappetence.20,23–25 In cats, inappetence appears to be the most common AE. Although unlikely, it is possible for erosions and ulcers to be silent and occur prior to any clinical signs.23,26 Studies