Which analgesic is approved in horses for colic analgesia and in dogs as a postoperative analgesic, administered IV or IM and described as less sedative than other opioids?

• A. Buprenorphine
• B. Morphine
• C. Diphenoxylate
• D. Pentazocine

Answer: (D)

Pentazocine works because it has a mixed opioid receptor action: it mainly stimulates kappa receptors while acting as a partial mu antagonist/partial agonist. This receptor profile provides meaningful analgesia, especially for visceral pain such as colic, but with less sedation and respiratory depression than a full mu opioid like morphine. That makes it a practical choice for horses needing colic analgesia where you want effective pain relief without oversedation, and for dogs as a postoperative analgesic where gentler CNS effects are advantageous.

Its use IV or IM allows flexible, rapid-onset dosing in both species, aligning with the need for timely analgesia in the perioperative period and in acute abdominal pain in horses. By contrast, pure mu agonists (like morphine) tend to cause more sedation and respiratory depression; a pure mu agonist isn’t described as having that lower-sedation advantage. Diphenoxylate isn’t a typical analgesic for postoperative or colic pain. Buprenorphine, while useful and long-acting, is a partial mu agonist with a different clinical niche and isn’t the agent described here for this specific equine and canine use.