Ketamine for acute and chronic pain: beyond anaesthesia

Ketamine's clinical role has expanded beyond anesthesia into a mechanism-based, non-opioid analgesic used across acute, perioperative, and chronic pain settings. As a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine attenuates central sensitization, modulates opioid tolerance, and enhances descending inhibitory control. At subanaesthetic doses (0.1-0.5 mg/kg), it consistently reduces pain scores and postoperative opioid consumption while maintaining hemodynamic and respiratory stability. In acute and perioperative care, analgesic efficacy is comparable to opioids, though clear superiority has not been demonstrated. In chronic pain, particularly complex regional pain syndrome (CRPS), multi-day infusions provide temporary relief, but durability remains limited. In cancer-related pain, ketamine offers adjuvant benefits for opioid-refractory syndromes with variable outcomes. Short-term adverse effects such as dizziness and mild dysphoria are common, whereas psychomimetic symptoms, hepatobiliary injury, and cystitis restrict prolonged use. Overall, ketamine provides context-dependent, opioid-sparing analgesia with defined but specific clinical utility. Its evolving role in pain management will likely remain targeted, emphasizing patient selection, standardized dosing, and realistic expectations for benefit.