Which of the following is NOT a common analgesic agent?

Ketamine, while used for analgesia in some contexts, is primarily classified as an anesthetic agent. It works by acting as an NMDA receptor antagonist, producing dissociative anesthesia rather than serving as a traditional analgesic.

On the other hand, codeine, meperidine, and morphine are all opioids that are widely recognized and utilized specifically for their analgesic properties. They directly interact with opioid receptors in the central nervous system to alleviate pain effectively. Codeine is often used for mild to moderate pain, meperidine for moderate to severe pain, and morphine is a stronger opioid, commonly used for severe pain management. Therefore, ketamine stands out from these agents due to its primary indication as an anesthetic rather than a primary analgesic.