Analgesics are an essential component to treating a variety of painful oral conditions in dogs and cats. Chronic pain and acute pain associated with oral surgery comprise the majority of pain states where analgesics are considered. Individual patient circumstances vary considerably and knowledge of individual agents and their mechanisms help us choose the correct analgesics for each patient.
National Pet Dental Health Month in February is a reminder of the importance of providing state-of-the-art oral care for our patients year round. Managing periodontal disease is by far the most common problem we encounter as general practitioners and specialists alike.
Proper diagnosis of periodontal lesions involves a complete oral examination, periodontal probing and full-mouth dental radiography. Periodontal lesion therapy involves painful procedures including periodontal flap surgery and tooth extraction, requiring appropriate analgesic choices.
Pre-emptive intraoperative and postoperative pain control should be considered in cases where surgical manipulation is expected to result in postoperative pain. A multimodal approach dictates the use of two or more analgesics to eliminate high doses required when using individual agents.
Pure mu agonist opiates such as morphine and hydromorphone provide the basis for optimal pain management for oral surgery. These agents should be used pre-emptively when significant postoperative pain is expected.
Examples would include any surgery where significant chronic pain has been present (Figure 1), flap-based extractions (Figures 2A and B) and cancer surgery requiring bone excision. Mixed agonist/antagonist opiates such as buprenorphine can be considered when mild to moderate postoperative pain is anticipated.
Such cases might include mild to moderate tissue manipulation for biopsies, periodontal disease, gingivectomy and oral mass removal not requiring bone intervention.
Combining opiates with an NSAID or an alpha-2 agonist (medetomidine) allows individual agent dosage reduction and more effective pain relief.
Regional nerve blocks using local anesthetics and continuous rate infusions (CRI) provide numerous benefits. Regional blockade and/or CRI maximize patient safety by allowing lower concentrations of the inhalant to be administered. The use of either technique minimizes or eliminates the need for additional postoperative analgesics immediately postoperatively.
Managing chronic pain requires special consideration to the pathophysiology involved in maintenance and exacerbation of the chronic pain state. Local pain has a significant inflammatory component.
Cytokines and chemokines including postaglandins, bradykinin and histamine are released locally. These substances sensitize peripheral nerve endings. Histamine in particular potentiates vasodilation and extravasation of additional mediators beyond the locus of inflammation.
This results in extension of pain into otherwise normal tissue increasing sensitivity. NSAIDs are particularly important as part of the treatment regimen in chronic oral pain for this very reason.
Chronic oral pain states also sensitize central pain mechanisms in the brain stem. Peripheral sensitization results in a buildup of excitory neurotransmittors in this that sensitize receptors centrally.
NMDA receptor stimulation in the brain stem enhances the peripheral pain response, making it difficult to control. Specific NMDA receptor antagonists like ketamine can be used to block this receptor site making the oral pan more manageable.
Loading doses of ketamine followed by continuous rate infusions are the treatment of choice at this time for countering this central component of chronic pain maintenance. The addition of an opiate following a loading dose is generally utilized along with ketamine pre-emptively, intraoperatively and postoperatively to maximize analgesia in cases like CUPS and feline stomatitis.
Lidocaine can be added to the infusions for canines. Excellent spreadsheets for calculation of CRI loading doses and infusion rates exist at www.VASG.org.
Chronic conditions that cannot be surgically approached due to financial or other reasons can often be controlled using oral NMDA receptor antagonists like dextromethorphan or amantidine in combination with opiates and NSAIDs.
Medical management should be considered a priority for cases of existing or anticipated oral pain in our patients.
As you can see analgesics are essential components in veterinary dentistry and a large component of successful case management.
Dr. Beckman, DVM, FAVD, Dipl. AVDC, AAPM, is the president of the American Veterinary Dental Society.