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Gabapentin
Gabapentin, a structural analog of γ-aminobutyric acid (GABA), is a widely prescribed medication for epilepsy and neuropathic pain. Despite its GABA-like structure, it does not directly interact with GABA receptors. This article integrates evidence from the British National Formulary (BNF), Lippincott Textbook of Pharmacology, and Lange Basic & Clinical Pharmacology to detail its mechanism of action, clinical applications, dosing guidelines, side effects, precautions, drug interactions, and pharmaceutical nomenclature
Gabapentin’s therapeutic effects stem from its ability to:
Modulate Calcium Channels:
Binds to the α2δ subunit of voltage-gated calcium channels in the central nervous system, reducing calcium influx into neurons. This inhibits the release of excitatory neurotransmitters like glutamate and substance P, dampening neuronal hyperexcitability (Lippincott).
Indirect GABA Effects:
Increases synaptic GABA levels indirectly, though it does not bind to GABA receptors or inhibit GABA metabolism (Lange).
BNF-Approved Indications:
Epilepsy: Adjunctive therapy for focal seizures (with or without secondary generalization).
Neuropathic Pain: Management of postherpetic neuralgia, diabetic neuropathy, and chronic pain syndromes.
Off-Label Uses:
Restless Legs Syndrome: Reduces sensory discomfort and urge to move legs (Lange).
Migraine Prophylaxis: Decreases frequency of attacks in some patients.
Anxiety Disorders: Limited evidence for generalized anxiety and social phobia (Lippincott).
Epilepsy:
Adults: Start at 300 mg once daily, gradually increasing to 900–1800 mg/day in three divided doses (max 3600 mg/day).
Elderly/Renal Impairment: Adjust based on creatinine clearance (CrCl):
CrCl 30–60 mL/min: Max 900 mg/day.
CrCl 15–29 mL/min: Max 600 mg/day.
CrCl <15 mL/min: Max 300 mg/day (BNF).
Neuropathic Pain:
Initiate at 300 mg/day, titrating to 1800–3600 mg/day as tolerated (BNF).
Administration Tips:
Take with food to improve absorption.
Avoid abrupt discontinuation (taper over ≥1 week to prevent withdrawal seizures).
Common:
Central Nervous System: Dizziness (20%), somnolence, fatigue, ataxia.
Gastrointestinal: Nausea, dry mouth.
Peripheral Edema: Occurs in ~8% of patients (BNF).
Serious but Rare:
Hypersensitivity Reactions: Angioedema, Stevens-Johnson syndrome.
Psychiatric Effects: Suicidal ideation (0.43% risk; monitor mood changes).
Withdrawal Symptoms: Seizures, anxiety, insomnia if stopped suddenly (Lippincott).
Contraindications: Hypersensitivity to gabapentin or excipients.
Renal Impairment: Mandatory dose reduction; avoid in severe impairment (CrCl <15 mL/min).
BNF Category: Use only if benefits outweigh risks; limited human data suggest possible skeletal malformations.
Lange Note: Animal studies show developmental toxicity.
Elderly Patients: Higher risk of dizziness, falls, and renal impairment; monitor renal function.
Abuse Potential: Increasing reports of recreational misuse, particularly when combined with opioids (Lippincott).
Antacids: Aluminum/magnesium-containing antacids reduce gabapentin absorption by ~20%; administer gabapentin ≥2 hours after antacids (BNF).
CNS Depressants:
Alcohol, Opioids, Benzodiazepines: Potentiate sedation, respiratory depression, and overdose risk (Lange).
Opioids:
Synergistic CNS depression; U.S. FDA warns of increased mortality with combined use (Lippincott).
Generic Name: Gabapentin.
Brand Names:
UK (BNF): Neurontin®, Gabapentin Teva®.
US: Gralise® (extended-release), Horizant® (for restless legs syndrome).
