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Horizant Side Effects Center
Medical Editor: John P. Cunha, DO, FACOEP
Horizant (gabapentin enacarbil) is an anticonvulsant drug prescribed for the treatment of moderate-to-severe primary Restless Legs Syndrome (RLS) in adults. Horizant is not recommended for patients who are required to sleep during the daytime and remain awake at night. Common side effects if Horizant include:
- loss of coordination, or
- blurred vision.
A small number of people who take anticonvulsants such as Horizant may experience depression, suicidal thoughts or attempts, or other mental/mood problems. Tell your doctor immediately if this occurs.
Horizant is to be taken once per day with food at about 5 PM. Tablets should be swallowed whole and should not be cut, crushed, or chewed. Horizant may interact with other medications that contain gabapentin, and other products that cause drowsiness including alcohol, antihistamines, drugs for sleep or anxiety, muscle relaxants, narcotic pain relievers, and allergy or cough-and-cold products. Tell your doctor all medications and supplements you use. Tell your doctor if you are pregnant or plan to become pregnant before using Horizant; it is unknown if it would affect a fetus. You should tell your doctor if you are breastfeeding or plan to breastfeed. In the body, Horizant becomes a drug called 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.
Our Horizant (gabapentin enacarbil) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
What is Patient Information Overview?
A concise overview of the drug for the patient or caregiver from First DataBank.
Horizant Overview - Patient Information: Side Effects
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
A small number of people who take anticonvulsants for any condition (such as seizure, bipolar disorder, pain) may experience depression, suicidal thoughts/attempts, or other mental/mood problems. Tell your doctor immediately if you or your family/caregiver notice any unusual/sudden changes in your mood, thoughts, or behavior including signs of depression, suicidal thoughts/attempts, thoughts about harming yourself.
Get medical help right away if you have any serious side effects, including: unusual fever, swollen glands, yellowing skin/eyes, unusual tiredness, dark urine, change in the amount of urine, chest pain.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US -
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.
Read the entire patient information overview for Horizant (Gabapentin Enacarbil Extended-Release Tablets)
What is Prescribing information?
The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.
Horizant FDA Prescribing Information: Side Effects
The following adverse reactions are described in more detail in the WARNINGS AND PRECAUTIONS section of the label:
Clinical Trials Experience
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice.
In all controlled and uncontrolled trials across various patient populations, more than 2,300 patients have received HORIZANT orally in daily doses ranging from 600 to 3,600 mg.
Restless Legs Syndrome
The exposure to HORIZANT in 1,201 patients with RLS included 613 exposed for at least 6 months and 371 exposed for at least 1 year. HORIZANT in the treatment of RLS was studied primarily in placebo-controlled trials (n = 642), and in longterm follow-up studies. The population with RLS ranged from 18 to 82 years of age, with 60% being female and 95% being Caucasian.
The safety of HORIZANT in doses ranging from 600 to 2,400 mg has been evaluated in 515 patients with RLS in 3 double-blind, placebo-controlled, 12-week clinical trials. The 600-mg dose was studied in 2 of the 3 studies. Eleven out of 163 (7%) patients treated with 600 mg of HORIZANT discontinued treatment due to adverse reactions compared with 10 of the 245 (4%) patients who received placebo.
The most commonly observed adverse reactions ( ≥ 5% and at least 2 times the rate of placebo) in these trials for the 600-mg dose of HORIZANT were somnolence/sedation and dizziness (see Table 4). Table 4 lists treatment-emergent adverse reactions that occurred in ≥ 2% of patients with RLS treated with HORIZANT and numerically greater than placebo.
Table 4: Incidence of Adverse Reactions in 12-Week RLS
Studies Reported in ≥ 2% of Patients Treated With 600 or 1,200 mg
of HORIZANT and Numerically Greater Than Placebo
|Body System/Adverse Reaction||Placeboa
(N = 245) %
|HORIZANT 600 mg/dayb
(N = 163) %
|HORIZANT 1,200 mg/dayc
(N = 269) %
|Nervous system disorders|
|General disorders and administration site conditions|
|Feeling abnormal||< 1||< 1||3|
|Peripheral edema||1||< 1||3|
|Metabolism and nutritional disorders|
|Increased appetite||< 1||2||2|
|Ear and labyrinth disorders|
|Depression||< 1||< 1||3|
|Libido decreased||< 1||< 1||2|
|a Placebo was a treatment arm in each of the 3
double-blind, placebo-controlled, 12-week clinical trials.
b The 600-mg dose of HORIZANT was a treatment arm in 2 of the 3 double-blind, placebocontrolled, 12-week clinical trials.
c The 1,200-mg dose of HORIZANT was a treatment arm in each of the 3 double-blind, placebo-controlled, 12-week clinical trials.
Adverse reactions reported in these three 12-week studies in < 2% of patients treated with 600 mg of HORIZANT and numerically greater than placebo were balance disorder, blurred vision, disorientation, feeling drunk, lethargy, and vertigo.
The following adverse reactions were dose-related: somnolence/sedation, dizziness, feeling drunk, libido decreased, depression, headache, peripheral edema, and vertigo.
The exposure to HORIZANT in 417 patients with PHN included 207 patients exposed for at least 3 months. Overall, the mean age of patients in the PHN studies ranged from 61 to 64 years of age across dose groups; the majority of patients were male (45% to 61%) and Caucasian (80% to 98%).
The safety of HORIZANT in doses ranging from 1,200 to 3,600 mg has been evaluated in 417 patients with PHN in 3 clinical studies. The principal efficacy study evaluating the efficacy and safety of HORIZANT in the management of PHN was a 12-week, double-blind, multicenter study comparing 1,200 mg/day, 2,400 mg/day and 3,600 mg/day to placebo. Six out of 107 (6%) patients treated with 1,200 mg of HORIZANT discontinued treatment due to adverse events compared with 12 of the 95 (13%) patients who received placebo.
The most commonly observed adverse reactions ( ≥ 10% and greater than placebo) in this trial for the 1,200 mg dose of HORIZANT were dizziness, somnolence, and headache (see Table 5). Table 5 lists treatment-emergent adverse reactions that occurred in ≥ 2% of patients with PHN treated with HORIZANT 1,200 mg/day and numerically greater than placebo.
Table 5: Incidence of Adverse Reactions (in At Least
2% of Patients Treated With 1,200 mg/day of HORIZANT and Numerically Greater
Than the Placebo Rate) Reported in All Patients in the 12-Week PHN Study
|Body System/Adverse Reaction||Placebo
(N = 95) %
|HORIZANT 1,200 mg/day
(N = 107) %
|HORIZANT 2,400 mg/day
(N = 82) %
|HORIZANT 3,600 mg/day
(N = 87) %
|General disorders and administration site conditions|
|Psychiatric disorders Insomnia||2||3||5||7|
|Metabolism and nutritional disorders|
The following adverse reactions were also reported as ≥ 2% at 2,400 mg/day and/or 3,600 mg/day and appeared to be dose-related but were < 2% at 1,200 mg/day: balance disorder, confusional state, depression, dry mouth, flatulence, increased appetite, irritability, and vertigo. Dizziness, somnolence, fatigue, and insomnia appeared to show a dose relationship.
Adverse Events Associated With Gabapentin
Read the entire FDA prescribing information for Horizant (Gabapentin Enacarbil Extended-Release Tablets)
Additional Horizant Information
Horizant - User Reviews
Horizant User Reviews
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Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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