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Gabapentin

Brands and Forms

  • Neurontin
    • capsule: 100mg, 300mg, 400mg
    • tablet: 600mg, 800mg
    • liquid: 250mg/5ml

Uses of Gabapentin

In psychiatry, Gabapentin can be used as an adjunct in the treatment of Social Phobia and Panic Disorder, and is also a good choice for treating anxiety symptoms in Bipolar Disorder.

In general medicine, Gabapentin is used to treat seizure disorders and neuropathic pain.

How Gabapentin Works

Gabapentin is an anticonvulsant. It binds to the alpha 2 delta subunit of voltage-gated calcium channels, which closes N and P/Q presynaptic calcium channels and thus decreases neuronal activity. Although it is structurally similar to GABA, it does not seem to have any actions on the GABA system.

Cautions when Using Gabapentin

Standard considerations.

Dosing of Gabapentin

The usual therapeutic range of Gabapentin for treating seizure disorders and neuropathic pain is 900-1800mg/day, given in divided doses 3 times a day. Similar dosing is recommended for use in psychiatric disorders. In some cases, doses of up to 3600mg/day can be used.

Initial dose is usually 300-900mg/day, and the dose can be increased in 300-900mg/day increments every few days.

When wanting to stop this medication, the dose should be decreased gradually over a period of 2-3 weeks.

Onset of action

Therapeutic effects usually require about 2 weeks to appear.

Kidney impairment

CrCl 60mL/min or higher: dose range 900-3600mg/day.
CrCl 30-59mL/min: dose range 400-1400mg/day.
CrCl 16-29mL/min: dose range 200-700mg/day.
CrCl 15 mL/min: dose range 100-300mg/day.
CrCl less than 15 mL/min: reduce dose in proportion to CrCl of 15mL/min (eg, patients with CrCl 7.5 mL/min should receive ½ daily dose of patient with CrCl 15 mL/min).

Liver impairment

No dose adjustment recommended.

Side-effects of Gabapentin

Below is a list of most of the reported side-effects of Gabapentin. Most of these side-effects occur in only a minority of individuals, and many also resolve with time while the medication is continued.

Cardiovascular: vasodilation; hypertension; peripheral edema.

Central Nervous System: dizziness; somnolence; ataxia; fatigue; nystagmus; tremor; weakness; abnormal thinking; headache; abnormal gait; amnesia; dysarthria; incoordination; hypesthesia; twitching; confusion; hyperkinesia; malaise; paresthesia; vertigo; abnormal movements.

Dermatologic: itchiness; rash.

Endocrine/Metabolic: weight gain; elevated blood sugar.

Eyes, Ears, Nose and Throat: diplopia; amblyopia; rhinitis; pharyngitis; conjunctivitis; otitis media; abnormal vision.

Gastrointestinal: diarrhea; dry mouth; constipation; nausea; abdominal pain; vomiting; dental abnormalities; dyspepsia; flatulence; increased or decreased appetite; gingivitis.

Genitourinary: impotence.

Hematologic: leukopenia; purpura.

Muskuloskeletal: muscle pains; joint pains; fractures.

Psychiatric: depressed mood; nervousness; irritability.

Respiratory: coughing; bronchitis; respiratory infection.

Common side-effects of Gabapentin

Dizziness, somnolence/ fatigue, unsteadiness, ankle swelling (peripheral edema).

Rare but serious side-effects of note of Gabapentin

None of note.

Gabapentin overdose

Diarrhea, double vision, drowsiness, lethargy, slurred speech.

Gabapentin and pregnancy

Category C: some animal studies show adverse effects at very high doses, but no controlled human studies have been done; should only be used in pregnancy if clearly needed and if benefits outweigh potential risks.

Medical Monitoring for Gabapentin

None for healthy individuals.

Drug Interactions with Gabapentin

  • Antacids may reduce bioavailability of Gabapentin. Take gabapentin 2 hours after antacid use.
  • Naproxen can increase absorption of Gabepentin
  • Morphine and Hydrocodone can increase Gabapentin blood levels.