Recommended Topic Related To:

Horizant

"June 8, 2012 -- The FDA has approved a drug currently used for restless leg syndrome to treat a common and painful complication of shingles, according to the medication's manufacturers.

Horizant (gabapentin enacarbil) has been approve"...

Horizant

Warnings
Precautions

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Effects on Driving

HORIZANT causes significant driving impairment. Patients being treated with HORIZANT should not drive until they have gained sufficient experience to assess whether HORIZANT impairs their ability to drive. However, prescribers and patients should be aware that patients' ability to assess their own driving competence, as well as their ability to assess the degree of somnolence caused by HORIZANT, can be imperfect.

In a 2-week simulated driving study in patients with RLS, a daily 1,200-mg dose of HORIZANT caused significant impairment within 2 hours and for up to 14 hours after dosing. The impairment was similar to that caused by the active control, a single oral dose of diphenhydramine 50 mg. The effect on driving at times other than 2 weeks is unknown. Whether the impairment is related to somnolence or other effects of HORIZANT is unknown. The 600-mg dose was not studied. Because a 600-mg/day dose of HORIZANT can cause significant somnolence, similar to that of the 1,200-mg/day dose, the 600- and 1,200-mg/day doses may have similar effects on driving behavior.

Somnolence/Sedation and Dizziness

HORIZANT causes somnolence/sedation and dizziness (see Table 3). Patients should be advised not to drive a car or operate other complex machinery until they have gained sufficient experience on HORIZANT to assess whether HORIZANT impairs their ability to perform these tasks.

During the controlled trials in patients with RLS, somnolence/sedation was reported in 20% of patients treated with 600 mg of HORIZANT per day compared with 6% of patients receiving placebo. In those patients treated with HORIZANT who reported somnolence, the somnolence persisted during treatment in about 30%. In the remaining patients, symptoms resolved within 3 to 4 weeks. Dizziness was reported in 13% of patients receiving 600 mg of HORIZANT per day compared with 4% of patients receiving placebo. In those patients treated with HORIZANT who reported dizziness, symptoms persisted during treatment in about 20%. Somnolence/sedation led to withdrawal in 2% of patients receiving 600 mg of HORIZANT per day. Dizziness led to withdrawal in 1% of patients receiving 600 mg of HORIZANT per day. The incidence of these adverse reactions was greater in the patients receiving 1,200 mg per day.

Lack of Interchangeability With Gabapentin

HORIZANT is not interchangeable with other gabapentin products because of differing pharmacokinetic profiles. The same dose of HORIZANT results in different plasma concentrations of gabapentin relative to other gabapentin products. [See CLINICAL PHARMACOLOGY.]

The safety and effectiveness of HORIZANT in patients with epilepsy have not been studied.

Suicidal Behavior and Ideation

HORIZANT (gabapentin enacarbil) is a prodrug of gabapentin, an antiepileptic drug (AED). AEDs increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Because HORIZANT is a prodrug of gabapentin, HORIZANT also increases this risk. Patients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.

Pooled analyses of 199 placebo-controlled clinical trials (monotherapy and adjunctive therapy) of 11 different AEDs showed that patients randomized to 1 of the AEDs had approximately twice the risk [adjusted relative risk 1.8, 95% confidence interval (CI): 1.2, 2.7] of suicidal thinking or behavior compared with patients randomized to placebo. In these trials, which had a median treatment duration of 12 weeks, the estimated incidence rate of suicidal behavior or ideation among 27,863 AED-treated patients was 0.43%, compared with 0.24% among 16,029 placebo-treated patients, representing an increase of approximately 1 case of suicidal thinking or behavior for every 530 patients treated. There were 4 suicides in drug-treated patients in the trials and none in placebo-treated patients, but the number is too small to allow any conclusion about drug effect on suicide.

The increased risk of suicidal thoughts or behavior with AEDs was observed as early as 1 week after starting drug treatment with AEDs and persisted for the duration of treatment assessed. Because most trials included in the analysis did not extend beyond 24 weeks, the risk of suicidal thoughts or behavior beyond 24 weeks could not be assessed.

The risk of suicidal thoughts or behavior was generally consistent among drugs in the data analyzed. The finding of increased risk with AEDs of varying mechanisms of action and across a range of indications suggests that the risk applies to all AEDs used for any indication. The risk did not vary substantially by age (5 to 100 years) in the clinical trials analyzed. Table 2 shows absolute and relative risk by indication for all evaluated AEDs.

Table 2: Risk by Indication for Antiepileptic Drugs in the Pooled Analysis

Indication Placebo Patients With Events Per 1,000 Patients Drug Patients With Events Per 1,000 Patients Relative Risk: Incidence of Events in Drug Patients/Incidence in Placebo Patients Risk Difference: Additional Drug Patients With Events Per 1,000 Patients
Epilepsy 1 3.4 3.5 2.4
Psychiatric 5.7 8.5 1.5 2.9
Other 1 1.8 1.9 0.9
Total 2.4 4.3 1.8 1.9

The relative risk for suicidal thoughts or behavior was higher in clinical trials for epilepsy than in clinical trials for psychiatric or other conditions, but the absolute risk differences were similar for the epilepsy and psychiatric indications.

Anyone considering prescribing HORIZANT must balance the risk of suicidal thoughts or behavior with the risk of untreated illness. Epilepsy and many other illnesses for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Should suicidal thoughts and behavior emerge during treatment, the prescriber needs to consider whether the emergence of these symptoms in any given patient may be related to the illness being treated.

Patients, their caregivers, and families should be informed that HORIZANT increases the risk of suicidal thoughts and behavior and should be advised of the need to be alert for the emergence or worsening of the signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers.

Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, has been reported in patients taking antiepileptic drugs, including gabapentin. HORIZANT is a prodrug of gabapentin. Some of these events have been fatal or life-threatening. DRESS typically, although not exclusively, presents with fever, rash, and/or lymphadenopathy, in association with other organ system involvement, such as hepatitis, nephritis, hematological abnormalities, myocarditis, or myositis sometimes resembling an acute viral infection. Eosinophilia is often present. Because this disorder is variable in its expression, other organ systems not noted here may be involved.

It is important to note that early manifestations of hypersensitivity, such as fever or lymphadenopathy, may be present even though rash is not evident. If such signs or symptoms are present, the patient should be evaluated immediately. HORIZANT should be discontinued if an alternative etiology for the signs or symptoms cannot be established.

Discontinuation of HORIZANT

When discontinuing HORIZANT, patients receiving the recommended dose of 600 mg daily can discontinue the drug without tapering. If the recommended dose is exceeded, the dose should be reduced to 600 mg daily for 1 week prior to discontinuation to minimize the potential of withdrawal seizure.

Tumorigenic Potential

In an oral carcinogenicity study, gabapentin enacarbil increased the incidence of pancreatic acinar cell adenoma and carcinoma in male and female rats [see Nonclinical Toxicology]. The clinical significance of this finding is unknown.

In clinical studies of gabapentin as adjunctive therapy in epilepsy comprising 2,085 patient-years of exposure in patients > 12 years of age, new tumors were reported in 10 patients (2 breast, 3 brain, 2 lung, 1 adrenal, 1 non-Hodgkin's lymphoma, 1 endometrial carcinoma in situ), and preexisting tumors worsened in 11 patients (9 brain, 1 breast, 1 prostate) during or up to 2 years following discontinuation of gabapentin. Without knowledge of the background incidence and recurrence in a similar population not treated with gabapentin, it is impossible to know whether the incidence reported in this cohort is or is not affected by treatment.

Patient Counseling Information

See Medication Guide.

Physicians should instruct their patients to read the Medication Guide before starting therapy with HORIZANT and to reread it upon prescription renewal for new information regarding the use of HORIZANT.

Effects on Driving

Patients should be told that HORIZANT can cause significant driving impairment. Accordingly, they should be advised not to drive a car until they have gained sufficient experience on HORIZANT to assess whether HORIZANT impairs their ability to drive. Patients should be told that it is not known how long this effect lasts.

Somnolence/Sedation and Dizziness

Patients should be told that HORIZANT can cause significant somnolence and dizziness. This typically resolves within several weeks of initiating treatment. Accordingly, they should be told not to operate dangerous machinery until they have gained sufficient experience on HORIZANT to assess whether HORIZANT impairs their ability to operate dangerous machinery safely.

Suicidal Behavior and Ideation

Patients, their caregivers, and families should be counseled that HORIZANT may increase the risk of suicidal thoughts and behavior, and should be advised of the need to be alert for the emergence or worsening of symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts, behavior, or thoughts about self-harm. Behaviors of concern should be reported immediately to healthcare providers.

Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity

Patients should be instructed that multiorgan hypersensitivity reactions may occur with HORIZANT. Patients should contact their physician immediately if they experience any signs or symptoms of these conditions [see WARNINGS AND PRECAUTIONS].

Lack of Interchangeability With Gabapentin

Patients should be advised that doses of HORIZANT and other gabapentin products are not interchangeable.

Dosing Instructions

  • Patients should be instructed to take HORIZANT only as prescribed.
  • HORIZANT should be taken once daily with food at about 5 PM.
  • If the dose is not taken at the recommended time, the patient should take the next dose at about 5 PM the following day.
  • Tablets should be swallowed whole and should not be cut, crushed, or chewed.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

Carcinogenesis

Oral (gavage) carcinogenicity studies were conducted in mice and rats. In mice, gabapentin enacarbil was tested at doses of 500, 2,000, or 5,000 mg/kg/day for up to 104 weeks. There was no evidence of drug-related carcinogenicity. The highest dose tested is 40 times the RHD of 600 mg/day, on a body surface area (mg/m²) basis.

In rats, gabapentin enacarbil was tested at doses of 500, 2,000, or 5,000 mg/kg/day for up to 97 weeks in mid-dose males, 90 weeks in high-dose males, and 104 weeks in females. The plasma exposures (AUC) for gabapentin at these doses are approximately 10, 38, and 75 times, respectively, that in humans at the RHD. Increases in the incidence of pancreatic acinar adenoma and carcinoma were found in mid-dose males and high-dose males and females.

In 2-year dietary carcinogenicity studies of gabapentin, no evidence of drug-related carcinogenicity was observed in mice treated at doses up to 2,000 mg/kg/day. In rats, increases in the incidence of pancreatic acinar cell adenoma and carcinoma were found in male rats receiving the highest dose (2,000 mg/kg), but not at doses of 250 or 1,000 mg/kg/day. At 1,000 mg/kg/day, the plasma AUC for gabapentin is estimated to be approximately 25 times that in humans at the RHD.

Studies designed to investigate the mechanism of gabapentin-induced pancreatic carcinogenesis in rats indicate that gabapentin stimulates DNA synthesis in rat pancreatic acinar cells in vitro and thus may be acting as a tumor promoter by enhancing mitogenic activity. It is not known whether gabapentin has the ability to increase cell proliferation in other cell types or in other species, including human.

Mutagenesis

Gabapentin enacarbil was negative in in vitro bacterial reverse mutation (Ames) and in vivo rat micronucleus assays. In an in vitro human lymphocyte assay, there was an increase in the number of chromosomal aberrations with gabapentin enacarbil. This in vitro response was attributed to acetaldehyde released by hydrolysis of gabapentin enacarbil during the incubation period. Acetaldehyde is known to cause chromosome aberrations in vitro, but is readily metabolized in vivo. The small quantity of acetaldehyde formed from gabapentin enacarbil in vivo is rapidly cleared by normal metabolic activity.

Impairment of Fertility

Oral administration of gabapentin enacarbil (doses of 0, 200, 1,000, or 5,000 mg/kg/day) to male and female rats prior to and throughout mating and continuing in females up to day 7 of gestation resulted in no adverse effects on fertility. The highest dose tested is approximately 80 times the RHD on a mg/m² basis.

Use In Specific Populations

Pregnancy

Pregnancy Category C

There are no adequate and well-controlled studies with HORIZANT in pregnant women. In nonclinical studies in rat and rabbits, administration of gabapentin enacarbil was developmentally toxic when administered to pregnant animals at doses and gabapentin exposures greater than those used clinically. HORIZANT should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

When pregnant rats were administered gabapentin enacarbil (oral doses of 200, 1,000, or 5.000 mg/kg/day) throughout the period of organogenesis, embryo-fetal mortality was increased at the 2 highest doses and fetal body weights were decreased at the high dose. The no-effect dose for embryo-fetal developmental toxicity in rats is approximately 3 times the recommended human dose (RHD) of 600 mg/day on a body surface area (mg/m²) basis.

When pregnant rabbits were administered gabapentin enacarbil (oral doses of 200, 500, or 2,500 mg/kg/day) throughout the period of organogenesis, embryo-fetal mortality was increased and fetal body weights were decreased at the high dose. The no-effect dose for embryo-fetal developmental toxicity in rabbits (500 mg/kg/day) is approximately 16 times the RHD on a mg/m² basis.

When female rats were administered gabapentin enacarbil (oral doses of 200, 1,000, or 5.000 mg/kg/day) throughout the pregnancy and lactation periods, offspring growth and survival were decreased at the two highest doses. The no-effect dose for pre- and post-natal developmental toxicity in rats is approximately 3 times the RHD on a mg/m² basis.

In reproductive and developmental studies of gabapentin, developmental toxicity was observed at all doses tested. Increased incidences of hydroureter and/or hydronephrosis were observed in rat offspring following treatment of pregnant animals in studies of fertility and general reproductive performance, embryo-fetal development, and peri- and post-natal development. Overall, a no-effect dose was not established. In mice, treatment of pregnant animals with gabapentin during the period of organogenesis resulted in delayed fetal skeletal ossification at all but the lowest dose tested. When pregnant rabbits were treated with gabapentin during the period of organogenesis, an increase in embryo-fetal mortality was observed at all doses of gabapentin tested.

In a published study, gabapentin (400 mg/kg/day) was administered by intraperitoneal injection to neonatal mice during the first postnatal week, a period of synaptogenesis in rodents (corresponding to the last trimester of pregnancy in humans). Gabapentin caused a marked decrease in neuronal synapse formation in brains of intact mice and abnormal neuronal synapse formation in a mouse model of synaptic repair. Gabapentin has been shown in vitro to interfere with activity of the a25 subunit of voltage-activated calcium channels, a receptor involved in neuronal synaptogenesis. The clinical significance of these findings is unknown.

Labor and Delivery

The effect of HORIZANT on labor and delivery is unknown.

Nursing Mothers

It is not known whether gabapentin derived from HORIZANT is secreted in human milk; however, gabapentin is secreted into human milk following oral administration of gabapentin products. Because of the potential for adverse reactions in nursing infants from HORIZANT, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness of HORIZANT in pediatric patients have not been studied.

Geriatric Use

Of the 515 patients treated with HORIZANT in the 3 double-blind, placebo-controlled, 12-week clinical trials for RLS, 11% were 65 to 74 years of age and 1% were 75 years of age and older. Clinical trials of HORIZANT did not include a sufficient number of patients 65 years and older to determine whether they respond differently from younger individuals.

Gabapentin is known to be almost exclusively excreted by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, the frequency of dosing may need to be adjusted based on calculated creatinine clearance in these patients [see DOSAGE AND ADMINISTRATION].

Renal Impairment

The dose of HORIZANT should be adjusted in patients with renal impairment [see DOSAGE AND ADMINISTRATION, CLINICAL PHARMACOLOGY].

Last reviewed on RxList: 4/27/2012
This monograph has been modified to include the generic and brand name in many instances.

Warnings
Precautions
A A A

Horizant - User Reviews

Horizant User Reviews

Now you can gain knowledge and insight about a drug treatment with Patient Discussions.

Here is a collection of user reviews for the medication Horizant sorted by most helpful. Patient Discussions FAQs

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.


Women's Health

Find out what women really need.