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Generic name: gabapentin enacarbil
Drug class: Gamma-aminobutyric acid analogs

Medically reviewed by  A Ras MD.

What is Horizant?

Horizant is a prescription medicine used to treat adults with moderate-to-severe primary Restless Legs Syndrome (RLS), pain from damaged nerves (postherpetic pain) that follows healing of shingles (a painful rash that comes after a herpes zoster infection).

Horizant is not for people with RLS who need to sleep during the daytime and need to stay awake at night.

Horizant is not the same medicine as gabapentin (for example, Neutronin or Gralise) and should not be used in its place.

It is not known if Horizant is safe and effective in children.


HORIZANT (gabapentin enacarbil) is a prodrug of gabapentin. Gabapentin enacarbil is described as (1-{[({(1RS)-1-[(2-Methylpropanoyl)oxy]ethoxy}carbonyl)amino]methyl} cyclohexyl) acetic acid. It has a molecular formula of C16H27NO6 and a molecular weight of 329.39. It is a racemate and has the following structural formula:

Chemical Structure

Gabapentin enacarbil is a white to off-white crystalline solid with a melting onset of approximately 64°C and a solubility of 0.5 mg/mL in water and 10.2 mg/mL in phosphate buffer (pH 6.3).

HORIZANT is administered orally. Each HORIZANT Extended-Release Tablet contains 300 mg or 600 mg of gabapentin enacarbil and the following inactive ingredients: colloidal silicon dioxide, dibasic calcium phosphate dihydrate, glyceryl behenate, magnesium stearate, sodium lauryl sulfate, and talc.

Mechanism of Action

Gabapentin enacarbil is a prodrug of gabapentin and, accordingly, its therapeutic effects in RLS and PHN are attributable to gabapentin.

The precise mechanism by which gabapentin is efficacious in RLS and PHN is unknown.

The mechanism of action by which gabapentin is efficacious in PHN is unknown but in animal models of analgesia, gabapentin prevents allodynia (pain-related behavior in response to a normally innocuous stimulus) and hyperalgesia (exaggerated response to painful stimuli). Gabapentin prevents pain-related responses in several models of neuropathic pain in rats and mice (e.g., spinal nerve ligation models, spinal cord injury model, acute herpes zoster infection model). Gabapentin also decreases pain-related responses after peripheral inflammation (carrageenan footpad test, late phase of formalin test), but does not alter immediate pain-related behaviors (rat tail flick test, formalin footpad acute phase). The relevance of these models to human pain is not known.

Gabapentin is structurally related to the neurotransmitter gamma-aminobutyric acid (GABA) but has no effect on GABA binding, uptake, or degradation. Gabapentin enacarbil and gabapentin have been tested in radioligand binding assays, and neither exhibited affinity for a number of other common receptor, ion channel, or transporter proteins.

In vitro studies have shown that gabapentin binds with high affinity to the α2δ subunit of voltage-activated calcium channels; however, the relationship of this binding to the therapeutic effects of gabapentin enacarbil in RLS and PHN is unknown.

What is the most important information I should know about Horizant?

Horizant can cause serious side effects:

1. Do not drive after taking your dose of Horizant until you know how Horizant affects you, including the morning after you take your dose. Do not operate heavy machinery or do other dangerous activities until you know how Horizant affects you. Horizant can cause sleepiness, dizziness, slow thinking, and can affect your coordination. Ask your healthcare provider when it would be okay to do these activities.

2. Horizant may cause suicidal thoughts or actions in a very small number of people, about 1 in 500.
Call a healthcare provider right away if you have any of these symptoms, especially if they are new, worse, or worry you:

  • thoughts about suicide or dying
  • attempt to commit suicide
  • new or worse depression
  • new or worse anxiety
  • feeling agitated
  • new or worse restlessness
  • panic attacks
  • new or worse trouble sleeping (insomnia)
  • new or worse irritability
  • acting aggressive, being angry, or violent
  • acting on dangerous impulses
  • an extreme increase in activity and talking (mania)
  • other unusual changes in behavior or mood

How can I watch for early symptoms of suicidal thoughts and actions?

  • Pay attention to any changes, especially sudden changes, in mood, behaviors, thoughts, or feelings.
  • Keep all follow-up visits with your healthcare provider as scheduled.
  • Call your healthcare provider between visits as needed, especially if you are worried about symptoms.

Do not stop Horizant without first talking to a healthcare provider.
Suicidal thoughts or actions can be caused by things other than medicines. If you have suicidal thoughts or actions, your healthcare provider may check for other causes.

3. Horizant may cause a serious or life-threatening allergic reaction that may affect your skin or other parts of your body such as your liver or blood cells. You may or may not have rash with these types of reactions. Call a healthcare provider right away if you have any of the following symptoms:

  • skin rash
  • hives
  • fever
  • swollen glands that do not go away
  • swelling of your lips or tongue
  • yellowing of your skin or eyes
  • unusual bruising or bleeding
  • severe fatigue or weakness
  • unexpected, severe muscle pain
  • frequent infections

These symptoms may be the first signs of a serious reaction. A healthcare provider should examine you to decide if you should continue taking Horizant.

4. Serious breathing problems. Serious breathing problems can occur when Horizant is taken with other medicines that can cause severe sleepiness or decreased awareness, or when it is taken by someone who already has breathing problems. Watch for increased sleepiness or decreased breathing when starting Horizant or when the dose is increased. Get help right away if breathing problems occur.

What should I tell my healthcare provider before taking Horizant?

Before taking Horizant, tell your healthcare provider if you:

  • have or have had kidney problems or are on hemodialysis.
  • have or have had depression, mood problems, or suicidal thoughts or behavior.
  • have or have had seizures.
  • have a history of drug abuse.
  • have any other medical conditions.
  • are pregnant or plan to become pregnant.
    • It is not known if Horizant will harm your unborn baby. Talk to your healthcare provider if you are pregnant or plan to become pregnant while taking Horizant. You and your healthcare provider will decide if you should take Horizant while you are pregnant.
  • are breastfeeding or plan to breastfeed. Your body turns Horizant into another drug (gabapentin) that passes into your milk. It is not known if this can harm your baby. You and your healthcare provider should decide if you will take Horizant or breastfeed.
  • drink alcohol.

Tell your healthcare provider about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements.

Know the medicines you take. Keep a list of them and show it to your healthcare provider and pharmacist when you get a new medicine.

How should I take Horizant?

  • Take Horizant exactly as your healthcare provider tells you to take it. Your healthcare provider will tell you how much Horizant to take and when to take it.
  • Take Horizant tablets whole. Do not cut, crush, or chew your tablet.
  • Take Horizant tablets with food.
  • Do not stop taking Horizant without talking to your healthcare provider first. If you stop taking Horizant suddenly, you may develop side effects.
  • If you forget to take your medicine at the time recommended by your healthcare provider, just skip the missed dose. Take the next dose at your regular time. Do not take 2 doses at one time.
  • If you take too much Horizant, call your healthcare provider or go to the nearest hospital emergency room right away.

What should I avoid while taking Horizant?

  • Do not take other medicines that make you sleepy or dizzy while taking Horizant without first talking with your healthcare provider. Taking Horizant with medicines that cause sleepiness or dizziness may make your sleepiness or dizziness worse.
  • Do not take other gabapentin drugs (for example, Neurontin or Gralise) while you take Horizant.
  • Do not consume alcohol when taking Horizant.

What are the possible side effects of Horizant?

  • See “What is the most important information I should know about Horizant?”

The most common side effects of Horizant include:

  • sleepiness
  • dizziness
  • headache

Tell your healthcare provider if you have any side effect that bothers you or that does not go away.

These are not all the possible side effects of Horizant. For more information, ask your healthcare provider or pharmacist.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

General information about the safe and effective use of Horizant

Medicines are sometimes prescribed for purposes other than those listed in a Medication Guide. Do not use Horizant for a condition for which it was not prescribed. Do not give Horizant to other people, even if they have the same symptoms that you have. It may harm them.

This Medication Guide summarizes the most important information about Horizant. If you would like more information, talk with your healthcare provider.

You can ask your healthcare provider or pharmacist for information about Horizant that was written for healthcare professionals.

For more information about Horizant, go to www.HORIZANT.com or call 1-866-516-4950.

How should I store Horizant?

  • Store Horizant between 59° and 86°F (15° and 30°C).
  • Keep Horizant dry and away from moisture.
  • Keep Horizant tightly closed in the bottle provided to you. Do not remove any moisture control packs that may come in the bottle.

Keep Horizant and all medicines out of the reach of children.

What are the ingredients in Horizant?

Active ingredients: gabapentin enacarbil

Inactive ingredients: Both the 300 mg and 600 mg tablets contain colloidal silicon dioxide, dibasic calcium phosphate dihydrate, glyceryl behenate, magnesium stearate, sodium lauryl sulfate, and talc.



  • 30 Tablets
    NDC 53451-0103-1
  • Horizant®
    (gabapentin enacarbil)
    extended-release tablets
  • 300 mg
  • Dispense the accompanying
    Medication Guide
    to each patient.
  • Rx only
PRINCIPAL DISPLAY PANEL - 300 mg Tablet Bottle Label

Imprint GS LFG - Horizant gabapentin enacarbil 600 mg


  • 30 Tablets
    NDC 53451-0101-1
  • Horizant®
    (gabapentin enacarbil)
    extended-release tablets
  • 600 mg
  • Dispense the accompanying
    Medication Guide to each patient.
  • Rx only
  • arbor®
  • HZT-TL600-01
PRINCIPAL DISPLAY PANEL - 600 mg Tablet Bottle Label
Imprint GS TF7 - Horizant gabapentin enacarbil 300 mg


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