Which neurotransmitter system is primarily targeted by gabapentinoids in the management of neuropathic pain?

Explanation

## Gabapentinoids: Mechanism of Action in Neuropathic Pain **Key Point:** Gabapentinoids (gabapentin and pregabalin) bind to the α₂δ subunit of voltage-gated calcium channels (VGCCs) on presynaptic nerve terminals, reducing calcium influx and neurotransmitter release. **High-Yield:** This mechanism is distinct from: - ~~GABA agonism~~ (despite the name "gabapentin," it does NOT bind to GABA receptors) - ~~Opioid receptor activation~~ (gabapentinoids are non-opioid analgesics) - ~~Monoamine reuptake inhibition~~ (unlike SNRIs such as venlafaxine) ## Mechanism of Neuropathic Pain Relief ```mermaid flowchart TD A[Nerve injury/sensitization]:::outcome --> B[Upregulation of α2δ VGCC subunits]:::outcome B --> C[Increased presynaptic calcium influx]:::outcome C --> D[Excessive neurotransmitter release<br/>Glutamate, Substance P]:::outcome D --> E[Neuropathic pain signal]:::outcome E --> F[Gabapentinoid binds α2δ subunit]:::action F --> G[Reduced calcium influx]:::action G --> H[Decreased neurotransmitter release]:::action H --> I[Pain relief]:::outcome ``` **Clinical Pearl:** Gabapentinoids are particularly effective in: - Postherpetic neuralgia (PHN) - Diabetic peripheral neuropathy (DPN) - Neuropathic cancer pain - Fibromyalgia (pregabalin) **Mnemonic:** **α₂δ = ALPHA-2-DELTA** — the specific VGCC subunit targeted; this is NOT a GABA drug despite its name. ## Gabapentinoid Comparison | Property | Gabapentin | Pregabalin | |----------|-----------|----------| | Binding affinity to α₂δ | Lower | Higher (6× more potent) | | Bioavailability | 60% (saturable) | >90% (linear) | | Onset of action | Slower (days to weeks) | Faster (days) | | FDA approval for neuropathic pain | Yes (PHN, DPN) | Yes (PHN, DPN, fibromyalgia) | | Renal elimination | Yes (requires dose adjustment) | Yes (requires dose adjustment) | [cite:KD Tripathi 8e Ch 12]