Dosing and uses of Horizant (gabapentin)
Adult dosage forms and strengths
tablet, extended-release
- 300mg
- 600mg
Restless Leg Syndrome (RLS)
Indicated for moderate-to-severe primary restless legs syndrome
600 mg qDay with food at about 5:00 pm
Postherpetic neuralgia
600 mg PO x3 days, and then increase to 600 mg PO BId
Renal Impairment
CrCl >60 mL/min: 600 mg qDay
CrCl 30-59 mL/min: Start at 300 mg qDay; if needed may increase to 600 mg qDay
CrCL 15-29 mL/min: 300 mg qDay
CrCl <15 mL/min: 300 mg every other day
CrCl <15 mL/min and hemodialysis: Do not administer
Administration
Swallow tablet whole, do not cut, crush, or chew
Take with food
If dose not taken as scheduled, wait until next scheduled dose to resume administration
Discontinuation: Gradually taper downward; patients receiving 600 mg BID for postherpetic neuralgia should decrease dose to 600 mg qDay for 1 week
Pediatric dosage forms and strengths
Safety and effectiveness have not been studied
Geriatric dosage forms and strengths
May require a dose reduction depending on renal function (see Renal Impairment)
Postherpetic Neuralgia (Horizant)
600 mg PO x3 days, and then increase to 600 mg PO BId
Restless legs syndrome (Horizant)
Indicated for moderate-to-severe primary restless legs syndrome
600 mg PO qDay with food at about 5 Pm
Horizant (gabapentin) adverse (side) effects
>10%
Somnolence/sedation (10-27%)
Dizziness (13-30%)
Headache (7-15%)
Fatigue/asthenia (6-10%)
1-10%
Nausea (4-9%)
Fatigue/asthenia (6-10%)
Peripheral edema (6-7%)
Insomnia (3-7%)
Irritability (4%)
Weight increase (2-5%)
Blurred vision (2-5%)
Xerostomia (3-4%)
Flatulence (2-3%)
Vertigo (1-3%)
Peripheral edema (1-3%)
Drunk/abnormal sensation (1-3%)
Depression (1-3%)
Decreased libido (1-2%)
Warnings
Contraindications
None
Cautions
Not interchangeable with other gabapentin products because of differing pharmacokinetic profiles
Somnolence, sedation, and dizziness may cause significant driving impairment
Antiepileptic drugs increase risk of suicidal thoughts or behavior in patients taking these drugs for any indication; monitor for emergence or worsening depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior
Discontinue gradually to minimize potential of withdrawal seizure; if taking 600 mg BID (for PHN), decrease to 600 mg qDay for 1 week prior to discontinuation
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, reported; some of these events have been fatal or life-threatening; typically presents with fever, rash, and/or lymphadenopathy in association with other organ system involvement (eg, hepatitis, nephritis, hematological abnormalities, myocarditis, myositis) and may resemble an acute viral infection
Pregnancy and lactation
Pregnancy category: C
Limited available data in pregnancy; use caution
Lactation: Unknown whether distributed in breast milk
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Horizant (gabapentin)
Mechanism of action
GABA analog; structurally related to neurotransmitter GABA, but has no effect on GABA binding, uptake, or degradation; mechanism for analgesic and anticonvulsant activity unknown
Absorption
Bioavailability: 75% (with food); 42-65% (fasting)
Peak Plasma Time: 7.3 hr (with food); 5 hr (fasting)
Distribution
Protein Bound: <3%
Vd: 76 L
Metabolism
Gabapentin is not appreciably metabolized in humans
Gabapentin enacarbil undergoes extensive first-pass hydrolysis (primarily in enterocytes) to form gabapentin, carbon dioxide, acetaldehyde, and isobutyric acid
Not a substrate, inducer, or inhibitor of CYP450 isoenzymes
Elimination
Half-life: 5.1 – 6.0 hr
Dialyzable: yes
Renal clearance: 5 -7 L/hr
Total body clearance: 6-9.3 L/hr (oral)
Excretion: 94% (urine); 5% (feces)
Administration
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.
