Use of an injectable opioid and injectable NSAID is common for perioperative analgesia and pain management.3 Pure mu-opioid receptor agonists (eg, morphine, hydromorphone, methadone, fentanyl) act on mu receptors at the spinal and supraspinal level and are highly effective analgesics. Pure mu agonists can manage moderate to severe pain and provide a moderate level of sedation.4 Butorphanol (a mixed agonist/antagonist) and buprenorphine (a partial agonist) also act at spinal and supraspinal levels; however, they are generally preferred for mildly painful procedures.1 Butorphanol is also used for its reasonable sedative effects, commonly in conjunction with dexmedetomidine or acepromazine.
NSAIDs (eg, carprofen, meloxicam, robenacoxib) are also commonly used and effectively contribute to analgesia in acute painful situations (eg, surgery).5-7 The primary mechanism of action is inhibition of COX enzyme activity and subsequent reduction in prostaglandin synthesis that reduces inflammation. Other non-COX–mediated anti-inflammatory and analgesic activities (eg, activity at the 5-lipoxygenase pathway, activities impacting other proinflammatory enzyme pathways) have been proposed to contribute to the overall effectiveness of NSAID pain management.6
Opioids and NSAIDs are effective analgesics when used alone but generally provide better pain management when coadministered. A recent study demonstrated inadequate early postoperative analgesia when dogs received only opioid premedication prior to surgery.8
Protocols that use a pure mu agonist (eg, methadone) can be applied to other soft tissue surgeries, basic orthopedic procedures, and longer procedures. Top-up doses of opioids can be administered midsurgery when the procedure is longer than the duration of the premedication agent. For example, premedication with hydromorphone (0.1 mg/kg IM or IV) can be supplemented intraoperatively with another dose (0.05 mg/kg IV) if the procedure lasts >2 hours. NSAID administration can be preoperative or intraoperative, but waiting until the patient has returned to normal physiologic status postoperatively can help avoid potential negative impacts on renal function during anesthesia-induced hypotension.