Gabapentin: Drug Information
1. Drug Name
Generic Name
Gabapentin
Brand Name(s)
- Pakistan: Gabin, Gantin
- India: Gabapin, Gabantip
- US: Neurontin, Gralise
- UK: Neurontin
2. Pharmacological Class
Class
Anticonvulsant
Subclass
GABA Analog
3. Mechanism of Action
Gabapentin binds to the alpha-2-delta subunit of voltage-gated calcium channels in the central nervous system. This action inhibits excitatory neurotransmitter release and modulates neuronal excitability, though the exact mechanism of its analgesic and anticonvulsant effects is not fully understood.
4. Indications
Primary Indications
- Epilepsy: Adjunctive therapy for partial seizures with and without secondary generalization in adults and children over 3 years of age.
- Postherpetic Neuralgia: Management of postherpetic neuralgia in adults.
Off-label Uses
- Neuropathic pain
- Migraine prophylaxis
- Fibromyalgia
- Restless Legs Syndrome (RLS)
5. Dosage and Administration
Standard Dosage
For epilepsy:
- Initial: 300 mg once on Day 1, 300 mg twice on Day 2, and 300 mg three times on Day 3
- Maintenance: 300 mg to 600 mg three times daily
For postherpetic neuralgia:
- Initial: 300 mg once on Day 1, 300 mg twice on Day 2, and 300 mg three times on Day 3
- Maintenance: 600 mg to 1,800 mg/day in divided doses
Route of Administration
Oral (capsules, tablets, oral solution)
Special Populations
- Pediatric: Safety and efficacy in children under 3 years of age for epilepsy have not been established.
- Geriatric: Dose adjustments may be necessary due to age-related renal function decline.
6. Pharmacokinetics
Absorption
Gabapentin is absorbed in the small intestine via a saturable mechanism, with bioavailability decreasing with increasing dose. Peak plasma concentrations occur within 2-3 hours.
Distribution
Gabapentin is widely distributed throughout the body, but only about 20% is bound to plasma proteins.
Metabolism
Gabapentin is not significantly metabolized in humans and is excreted unchanged in the urine.
Excretion
Primarily excreted by the kidneys. Clearance is proportional to creatinine clearance.
Half-life
The elimination half-life of gabapentin is approximately 5 to 7 hours.
7. Contraindications
- Hypersensitivity to gabapentin or any of its components
8. Warnings and Precautions
- Increased risk of suicidal thoughts and behaviors
- Use with caution in patients with renal impairment
- May cause dizziness and somnolence
- Avoid abrupt discontinuation to prevent withdrawal seizures
9. Side Effects
Common Side Effects
- Dizziness
- Fatigue
- Weight gain
- Peripheral edema
Serious Side Effects
- Suicidal thoughts and behaviors
- Severe allergic reactions
- Respiratory depression
10. Drug Interactions
Major Interactions
- Opioids: Increased risk of CNS depression
- Antacids containing aluminum or magnesium: Decrease gabapentin absorption
Moderate Interactions
- Antidepressants: Increased risk of CNS side effects
Minor Interactions
- NSAIDs: No significant interactions but monitor for increased side effects
11. Pregnancy and Lactation
Pregnancy Category
Category C - Risk cannot be ruled out.
Breastfeeding Considerations
Gabapentin is excreted in human milk. Caution is advised when administered to a nursing woman.
12. Patient Counseling Information
- Take gabapentin exactly as prescribed and do not exceed the recommended dose.
- Gabapentin may cause dizziness and drowsiness; avoid driving or operating heavy machinery until you know how it affects you.
- Inform your healthcare provider about all medications you are taking to avoid potential interactions.
- Do not stop taking gabapentin abruptly without consulting your doctor.
- Report any new or worsening symptoms, including mood changes or suicidal thoughts, to your healthcare provider immediately.