What is the primary pharmacologic action of duloxetine relevant to neuropathic pain?

• A. Inhibition of serotonin and norepinephrine reuptake, enhancing descending pain inhibition.
• B. Blockade of NMDA receptors.
• C. GABA receptor agonism.
• D. Opioid receptor antagonism.

Answer: (C)

Duloxetine works by blocking the reuptake of serotonin and norepinephrine in the central nervous system, which raises their levels in synapses. This boosts the descending pain inhibitory pathways from the brainstem to the spinal cord, helping to dampen the transmission of pain signals at the spinal level. In neuropathic pain, strengthening this monoaminergic inhibition reduces abnormal excitability and central sensitization that drive persistent pain.

NMDA receptor blockade is a different mechanism (used by NMDA antagonists), GABA receptor agonism would enhance GABAergic inhibition directly (not how duloxetine works), and opioid receptor antagonism would counteract analgesia rather than produce it. The SNRI action on serotonin and norepinephrine reuptake best explains duloxetine’s benefit in neuropathic pain.