Gabapentin: 7 things you should know
Medically reviewed by C. Fookes, BPharm Last updated on Sep 10, 2018.
1. How it works
- Gabapentin is a medicine that may be used for the treatment of certain seizure disorders or nerve pain.
- Experts aren't sure exactly how gabapentin works, but research has shown that gabapentin binds strongly to a specific site (called the alpha2-delta site) on voltage-gated calcium channels. This action is thought to be the mechanism for its nerve-pain relieving and anti-seizure properties.
- Gabapentin enacarbil (brand name Horizant) is a prodrug of gabapentin which has been designed to overcome the limitations of gabapentin, such as poor absorption and a short duration of action. Gabapentin enacarbil is effective for restless legs syndrome (RLS) and postherpetic neuralgia (nerve pain that occurs following Shingles).
- Gabapentin belongs to the group of medicines known as anticonvulsants.
- May be used in addition to other medication to reduce seizure frequency in adults and children aged three and older with partial onset seizures.
- May be used in the management of postherpetic neuralgia (persistent nerve pain following Shingles infection) in adults.
- Gabapentin enacarbil (brand name Horizant) may be used to relieve restless legs syndrome (RLS) or nerve pain associated with postherpetic neuralgia. This prodrug of gabapentin only requires once-daily dosing.
- Gabapentin is available as a generic; however, not all generics are interchangeable with some branded versions of gabapentin.
- Gabapentin may be used off-label (this means for an indication that has not been approved by the FDA but may still have a place in therapy) for some other indications such as fibromyalgia, persistent hiccups, migraine prevention and hot flashes.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Dizziness, drowsiness, tiredness, fever, and nystagmus (a rapid and uncontrollable movement of the eyes). Drowsiness caused by gabapentin may affect your ability to drive or operate machinery. Alcohol and other drugs with sedative properties enhance this effect.
- May cause behavioral problems, hostility or aggression, or thought disturbances when used to treat epilepsy in children aged three to twelve years.
- Other side effects may include blurred vision, amblyopia (lazy eye), dry mouth, peripheral edema (fluid retention in the feet and hands), tremor, sexual dysfunction and gastrointestinal disturbances.
- Best titrated up slowly to reduce the risk of side effects; however, this may delay the onset of an effect.
- Similar to other anticonvulsant medicines, gabapentin may increase the risk of depression and suicidal thoughts, particularly in young adults under the age of 24.
- Gabapentin has been associated with a discontinuation syndrome when abruptly stopped. Symptoms include anxiety, insomnia, nausea, pain, and sweating. It should be tapered off slowly under a doctor's advice.
- The dosage of gabapentin needs to be reduced in kidney disease.
- Rarely, hypersensitivity reactions may occur. Symptoms may include fever, rash, swollen lymph nodes, swollen facial features or throat.
- May interact with some other medications including antacids, hydrocodone, morphine, and other drugs that cause sedation or dizziness. May also cause false positive results on some urinary protein tests.
- There have been some reports of gabapentin misuse and abuse, particularly in people with a history of drug abuse. Be alert for this possibility.
- Gabapentin requires three times daily administration because of its short duration of effect. Gabapentin enacarbil (brand name Horizant) only requires once-daily dosing.
- Only effective for partial onset seizures, not other types of seizure disorders.
- Some branded and generic forms of gabapentin are not interchangeable.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- The Neurontin brand of gabapentin can be taken with or without food. If you break a 600mg or 800mg Neurontin tablet in half, be sure to take the other half at your next dose or within 28 days.
- The Gralise brand of gabapentin cannot be substituted for other gabapentin products due to differing administration requirements (once daily versus three times daily for other products). Gralise should be taken with food at the evening meal. Gralise tablets should be swallowed whole; do not cut, crush, or chew.
- Horizant (gabapentin enacarbil) tablets should be swallowed whole and taken with food. For restless leg syndrome, take at roughly 5 PM in the evening. Do not cut, crush, or chew the tablet. Do not interchange Horizant with other gabapentin products.
- Use a manufacturer-provided or pharmacist-provided measuring cup calibrated for liquid formulations when measuring liquid doses of gabapentin. Do not use a kitchen measuring device or teaspoon because these may be inaccurate.
- For dosage schedules of three times daily do not allow more than 12 hours between doses.
- Monitor for mood changes and report any evidence of new or worsening mood or depression to the prescribing doctor.
- Do not take gabapentin at the same time as antacids such as Maalox or Gaviscon. Separate administration by at least two hours. Take exactly as directed by your doctor, do not increase or decrease the dose without his or her advice.
- Avoid operating machinery, driving, or performing tasks that require mental alertness if gabapentin makes your drowsy or impairs your judgment.
- The side effects of gabapentin, such as dizziness or drowsiness, may increase your risk of falling. Remove any fall hazards from your home if possible (such as loose rugs), and be careful when ascending or descending stairs.
- Talk to your doctor if you experience any worsening of your mood or if you develop any suicidal thoughts.
- Do not stop taking gabapentin without your doctor's advice as it may precipitate a withdrawal reaction (symptoms include agitation, disorientation, confusion). When the time comes to discontinue gabapentin your doctor will tell you how to taper it off.
- Seek urgent medical advice if you develop a rash, fever, difficulty breathing or facial swelling while taking gabapentin.
6. Response and Effectiveness
- Peak concentrations of gabapentin (immediate-release) occur within 2 to 3 hours. Although gabapentin may improve sleep problems due to nerve pain within a week, it may take up to two weeks for symptom relief from nerve pain to occur. A reduction in seizure frequency is usually apparent within a few weeks.
- Gabapentin enacarbil (brand name Horizant), a prodrug of gabapentin, is rapidly absorbed by nutrient transporters along the gastrointestinal tract and then quickly hydrolyzed to gabapentin. This means gabapentin enacarbil only needs to be given once a day. However, symptom relief from RLS or postherpetic neuralgia may take several days or weeks to develop.
- Immediate-release gabapentin capsules require three times daily dosing (except in kidney disease).
Medicines that interact with gabapentin may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with gabapentin. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may interact with gabapentin include:
- antacids, such as those containing aluminum and magnesium
- anti-anxiety medications, such as diazepam, lorazepam, and flunitrazepam
- antidepressants, such as amitriptyline, citalopram, fluoxetine, paroxetine
- antihistamines, such as chlorpheniramine, promethazine
- antipsychotics, such as aripiprazole, chlorpromazine, haloperidol
- narcotic pain relievers, such as oxycodone and morphine
- sedatives or sleeping pills
Alcohol may worsen the side effects of gabapentin such as drowsiness and dizziness.
Note that this list is not all-inclusive and includes only common medications that may interact with gabapentin. You should refer to the prescribing information for gabapentin for a complete list of interactions.
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use gabapentin only for the indication prescribed.
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