Gabapentin

1. Introduction

Gabapentin is a gamma-aminobutyric acid (GABA) analogue used to treat neuropathic pain, epilepsy, and other off-label conditions. Although it is structurally similar to GABA, it does not act directly on GABA receptors. Instead, it binds to voltage-gated calcium channels in the central nervous system, reducing nerve excitability and pain transmission.

2. Indications

  • Approved Indications:
    • Neuropathic pain (e.g., diabetic neuropathy, postherpetic neuralgia).
    • Epilepsy (adjunctive therapy for partial seizures with or without secondary generalisation).
  • Off-Label Uses:
    • Fibromyalgia.
    • Generalised anxiety disorder (GAD).
    • Restless legs syndrome (RLS).
    • Migraine prophylaxis.

3. Dosage

  • Adults:
    • Neuropathic pain: Start with 300 mg once daily, titrate up to 300 mg 3 times daily (maximum: 3600 mg/day).
    • Epilepsy: Start with 300 mg once daily, titrate up to 300 mg 3 times daily. Adjust based on response (maximum: 3600 mg/day).
  • Elderly:
    • Start with the lowest dose (e.g., 100–300 mg daily) and titrate slowly due to reduced renal clearance.
  • Children (≥6 years):
    • Epilepsy: Start with 10–15 mg/kg/day in 3 divided doses. Titrate up to 25–35 mg/kg/day.

4. Administration

  • Take orally with or without food.
  • Space doses evenly throughout the day (e.g., every 8 hours for three times daily dosing).
  • Do not abruptly discontinue; taper dose gradually over at least one week to prevent withdrawal symptoms.

5. Forms Available

  • Capsules: 100 mg, 300 mg, 400 mg.
  • Tablets: 600 mg, 800 mg.
  • Oral solution: 50 mg/mL.

6. Side Effects

6.1. Common Side Effects

  • Dizziness.
  • Drowsiness.
  • Fatigue.
  • Ataxia (lack of coordination).

6.2. Less Common Side Effects

  • Peripheral oedema.
  • Dry mouth.
  • Weight gain.

6.3. Rare but Serious Side Effects

  • Suicidal thoughts or behaviours.
  • Severe allergic reactions (e.g., angioedema).
  • Respiratory depression (especially with concomitant opioids or in elderly patients).

7. Warnings

  • Suicide Risk: Monitor for suicidal thoughts and behaviours, especially at the start of treatment.
  • CNS Depression: Avoid activities requiring mental alertness (e.g., driving) if experiencing drowsiness or dizziness.
  • Respiratory Depression: Risk is increased in patients using opioids or with underlying respiratory conditions.

8. Precautions

  • Use cautiously in patients with:
    • Renal impairment (dose adjustment required).
    • History of substance abuse (gabapentin misuse has been reported).
    • Concurrent CNS depressant use (e.g., alcohol, sedatives).

9. Interactions

  • Drug-Drug Interactions:
    • Opioids (e.g., morphine): Increased risk of respiratory depression and sedation.
    • Antacids: Reduce gabapentin absorption; take gabapentin at least 2 hours after antacids.
    • CNS depressants (e.g., benzodiazepines): Increased sedation and CNS depression.
  • Drug-Food Interactions:
    • No significant interactions, but alcohol may enhance drowsiness and dizziness.

10. Monitoring Parameters

  • Pain relief or reduction in seizure frequency.
  • Signs of CNS depression (e.g., excessive drowsiness, confusion).
  • Mood changes or emergence of suicidal thoughts.
  • Renal function (for dose adjustment in renal impairment).

11. Use in Children

  • Approved for use in children aged 6 years and older for epilepsy.
  • Not recommended for neuropathic pain in children due to insufficient evidence.

12. Use in Pregnancy

  • Category C: Use only if benefits outweigh risks. Gabapentin crosses the placenta, and its effects on the foetus are not well-studied. Consult a healthcare provider before use.

13. Use in Elderly

  • Safe for use, but start at the lowest dose due to increased risk of CNS side effects and reduced renal clearance.

14. Use in Kidney Disease

  • Dose Adjustments for Renal Impairment:
Creatinine Clearance (mL/min)Total Daily Dose (mg)
≥60900–3600 mg
30–59400–1400 mg
15–29200–700 mg
<15 or on dialysis100–300 mg (after dialysis)

15. Use in Liver Disease

  • No dose adjustment is required, as gabapentin is not metabolised in the liver.

16. Patient Counselling Points

  • Take gabapentin as prescribed. Do not adjust the dose or stop suddenly without consulting your doctor.
  • Report any unusual mood changes, suicidal thoughts, or increased anxiety to your doctor immediately.
  • Avoid alcohol and other sedatives to reduce the risk of drowsiness or respiratory depression.
  • Inform your doctor of all medications you are taking to avoid interactions.
  • Gabapentin may cause dizziness or drowsiness; avoid driving or operating heavy machinery until you know how it affects you.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
NeurontinPfizer$50–100 (30 tablets, 300 mg)
Gralise (ER Tablets)Depomed$200–300 (30 tablets, 600 mg)
Generic GabapentinVarious manufacturers$10–20 (30 tablets, 300 mg)

18. FAQs (15 Questions)

  1. What is gabapentin used for?
    Gabapentin is used to treat neuropathic pain and as adjunctive therapy for epilepsy.
  2. How does gabapentin work?
    It binds to calcium channels in the nervous system, reducing nerve excitability and pain transmission.
  3. How long does gabapentin take to work?
    Pain relief may take a few days to weeks, while seizure control may require consistent dosing over several weeks.
  4. Can gabapentin cause side effects?
    Yes, common side effects include dizziness, drowsiness, and fatigue.
  5. Is gabapentin addictive?
    While not classified as an addictive drug, gabapentin misuse has been reported, especially in those with a history of substance abuse.
  6. Can gabapentin be used during pregnancy?
    Use only if the benefits outweigh the risks. Consult your doctor before use.
  7. Can children take gabapentin?
    Yes, it is approved for children aged 6 years and older for epilepsy.
  8. How should gabapentin be taken?
    Take as prescribed, with or without food, and space doses evenly throughout the day.
  9. Can gabapentin cause weight gain?
    Yes, weight gain is a possible side effect, though not common.
  10. What should I do if I miss a dose?
    Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up.
  11. Can I drink alcohol while taking gabapentin?
    Avoid alcohol, as it may enhance drowsiness and dizziness.
  12. Does gabapentin interact with other medications?
    Yes, it interacts with opioids, antacids, and CNS depressants.
  13. Can gabapentin treat anxiety?
    While not officially approved, gabapentin is sometimes used off-label for anxiety.
  14. How should gabapentin be stored?
    Store at room temperature, away from moisture and heat.
  15. Can gabapentin be stopped abruptly?
    No, taper the dose gradually to prevent withdrawal symptoms such as seizures or increased pain.