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Gabapentin

Neurontin | Gralise | Horizant

FDA ApprovedCentral Nervous System AgentsAnticonvulsants
FDA: 1993Half-life: 5-7 hoursPregnancy: Category C

Overview

Binds to alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, reducing excitatory neurotransmitter release. Exact mechanism not fully understood.

Indications

  • Partial seizures (adjunctive therapy)
  • Postherpetic neuralgia
  • Neuropathic pain
  • Restless legs syndrome (Horizant)
  • Fibromyalgia (off-label)

Contraindications

  • Hypersensitivity to gabapentin

Classification

Central Nervous System AgentsAnticonvulsantsCentral Nervous System

Mechanism of Action

Binds to alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system, reducing excitatory neurotransmitter release. Exact mechanism not fully understood.

Pharmacodynamics

Structurally related to GABA but does not bind GABA receptors, alter GABA uptake, or act as a GABA agonist. Modulates calcium channel activity.

Pharmacokinetics

Absorption
Absorbed via L-amino acid transport system in gut. Absorption is saturable and dose-dependent (bioavailability decreases at higher doses).
Distribution
Not bound to plasma proteins. Crosses blood-brain barrier.
Metabolism
Not metabolized. Excreted unchanged.
Excretion
Renal (100% unchanged). Dose adjustment required in renal impairment.
Half-life
5-7 hours
Bioavailability
60% (300mg), 47% (400mg), 27% (1600mg) - inversely proportional to dose
Protein Binding
<3%

Dosage

Typical dosage: 300-600mg three times daily (up to 3600mg/day for seizures)

Available Forms

  • Capsule
  • Tablet
  • Oral solution
  • Extended-release tablet

Side Effects

Common

  • Somnolence
  • Dizziness
  • Ataxia
  • Fatigue
  • Peripheral edema

Serious

  • Respiratory depression (especially with opioids)
  • Suicidal ideation
  • Multiorgan hypersensitivity

Rare

  • Anaphylaxis
  • Rhabdomyolysis

Drug Interactions

major

Increased risk of CNS depression, respiratory depression, and death. Use lowest effective doses and monitor closely.

minor

Antacids containing aluminum/magnesium reduce gabapentin absorption by 20%. Take gabapentin at least 2 hours after antacids.

Warnings

Pregnancy

Category C

Toxicity

LD50 >8000 mg/kg (oral, rat)

Overdose

Symptoms: drowsiness, lethargy, slurred speech, double vision, diarrhea. Treatment: supportive care. Removable by hemodialysis.

References

Looking for patient-friendly information? Visit RemedyDoor for easy-to-read guides about this medication.