Pain Management in Small Animals with Lameness
Control of pain in lame or operative animals involves broad classes of compounds such as NSAIDs and opioids (also see Pain Assessment and Management). Analgesic agents can be administered via oral, parenteral (including constant-rate infusions), epidural, local, or transdermal routes. Nonpharmacologic pain management strategies include acupuncture therapy, massage, physical therapy, and diet.
Commonly used NSAIDs include deracoxib (4 mg/kg/day, PO), firocoxib (5 mg/kg/day, PO), meloxicam (dogs: 0.1 mg/kg/day, IV, SC, PO; cats: 0.1 mg/kg/day, IV, SC, PO, for 1–3 days), carprofen (2.2 mg/kg, PO, bid), ketoprofen (1 mg/kg/day, PO, IV, SC, IM), etodolac (12.5 mg/kg/day, PO), tepoxalin (10 mg/kg/day, PO), and aspirin (dogs: 22 mg/kg, PO, bid; cats: 10 mg/kg, PO, every 48 hr). The use of NSAIDs is contraindicated in animals with hepatic or renal insufficiency, gastroenteritis, or coagulopathy, and in animals receiving concurrent corticosteroid therapy.
Opioid analgesics bind to μ, κ, and δ receptors in the CNS to provide pain relief. Commonly used opioids include morphine (0.1 mg/kg, IV, IM, SC, every 3–4 hr), oxymorphone (0.05 mg/kg, IV, IM, SC, every 3–4 hr), hydromorphone (0.1 mg/kg, IV, IM, SC, every 2–4 hr), butorphanol (0.1 mg/kg, IV, IM, SC, every 2–4 hr in dogs and cats), and buprenorphine (0.01 mg/kg, IV, IM, SC, tid in dogs and cats, also transmucosal in cats). Opioid narcotics can be given with sedatives such as acepromazine (0.5 mg/kg, IV, IM, SC, every 4–6 hr) for enhanced efficacy of analgesia and sedation. Oxymorphone, hydromorphone, and butorphanol are more potent than morphine. Buprenorphine has the longest duration of action. Another opioid, fentanyl, is most frequently administered via transdermal patches applied for 3 days on shaved areas. Oral opioids used for pain relief include tramadol (5 mg/kg, tid), butorphanol (1 mg/kg, tid), hydromorphone (0.5 mg/kg, tid), codeine (1 mg/kg, tid), and oxycodone (0.3 mg/kg, tid).
Local administration of analgesics involves joint injections with morphine (1 mg diluted in 5 mL of saline), bupivicaine (1 mL/20 kg body wt), or lidocaine (1 mL/20 kg body wt) before joint surgery as a preemptive block of intracapsular pain receptors. Epidural morphine (0.1 mg/kg) in the lumbosacral space is also a useful adjunct for postoperative pain relief in the hindlimbs and for reduced anesthetic requirements. Corticosteroids are considered weak analgesic adjuncts, because they indirectly reduce pain by their primary action as local anti-inflammatory agents at the site of injury. Drugs used include prednisone or prednisolone (1–2 mg/kg/day, PO) or dexamethasone (1–2 mg/kg/day, IV). Their use is contraindicated during concurrent NSAID treatment.
Gabapentin (10 mg/kg, PO, bid) is a calcium channel blocker used to inhibit neurons stimulated by pain; it is useful for treatment of animals with chronic or neuropathic pain. Dexmedetomidine (5 mcg/kg/day, IM) and medetomidine (10 mcg/kg/day, IM) are newer analgesic-sedative, α2-receptor blocking agents useful to facilitate examinations or diagnostic evaluations.
Joint fluid modifiers (glucosamine, chondroiton sulfate, hyaluronan, pentosan polysulfate, omega-3 fatty acids) have received extensive attention in treating degenerative joint disease and alleviating discomfort. While contraindications and adverse effects are few, scientifically proven efficacy of these compounds is limited and most reports are regarded as anecdotal evidence. Stem cell therapy to alleviate pain and discomfort of diseased joints is also a newer modality for which scientific validity is pending.