Section 06 · Monograph

Gabapentin enacarbil

Reviewed Nov 2026FDA label

HorizantGabapentinoid (prodrug)

Indications

Moderate-to-severe primary Restless Legs Syndrome (RLS) in adults (FDA-approved).FDA-labeled
Management of postherpetic neuralgia (PHN) in adults (FDA-approved).FDA-labeled

Diabetic peripheral neuropathy (off-label extrapolation from gabapentin data)Off-label
Generalized anxiety disorder (limited evidence)Off-label

Gabapentin enacarbil is an inactive prodrug of gabapentin, rapidly and essentially completely hydrolyzed to gabapentin by nonspecific carboxylesterases after oral absorption.
Unlike gabapentin itself (absorbed via a saturable, low-capacity transporter limited to the proximal small bowel), gabapentin enacarbil is absorbed via high-capacity nutrient transporters (including monocarboxylate transporter type 1, MCT-1) expressed throughout the small intestine and colon, giving predictable, dose-proportional, near-complete absorption.
Gabapentin (the active moiety) binds with high affinity to the alpha-2-delta (α2δ-1) subunit of voltage-gated calcium channels, reducing calcium influx at nerve terminals and decreasing release of excitatory neurotransmitters; it is not a GABA-receptor agonist despite the name.
Clinically notable: as an alpha-2-delta ligand, gabapentin enacarbil is not associated with the augmentation phenomenon seen with dopaminergic RLS therapy, making it a preferred option for patients who develop augmentation on pramipexole or ropinirole.

RLS: 600 mg once daily, taken with food at approximately 5 PM. Doses above 600 mg provided no additional benefit and increased adverse reactions.
Postherpetic neuralgia (PHN): Start 600 mg once each morning for 3 days; increase to 600 mg twice daily beginning day 4. Maximum effective dose 1,200 mg/day (600 mg BID).
Tablets must be swallowed whole with food; do not chew, crush, or split.
Discontinuation: RLS patients on ≤600 mg once daily may generally stop without tapering; PHN patients (or RLS patients on higher-than-recommended doses) should taper over about 1 week given withdrawal seizure risk.

Renal dose adjustment — RLS: CrCl ≥60: 600 mg/day; CrCl 30-59: start 300 mg/day, may increase to 600 mg/day; CrCl 15-29: 300 mg/day; CrCl <15: 300 mg every other day; hemodialysis: not recommended.
Renal dose adjustment — PHN: CrCl ≥60: standard titration to 600 mg BID; CrCl 30-59: 300 mg AM x3 days then 300 mg BID, may increase to 600 mg BID; CrCl 15-29: 300 mg AM days 1 and 3, then 300 mg AM; CrCl <15: 300 mg every other day (AM); hemodialysis: 300 mg post-dialysis, may increase to 600 mg if needed.

No contraindications are listed in current FDA labeling ('Contraindications: None').
Practically: known hypersensitivity to gabapentin enacarbil, gabapentin, or any formulation component (angioedema, Stevens-Johnson-type reactions reported).
Not recommended for RLS patients who require daytime sleep and remain awake at night (e.g., shift workers).
Not recommended for RLS patients with renal impairment requiring hemodialysis.

Alcohol: accelerates release of gabapentin from the extended-release matrix, risking a rapid rise in plasma levels and increased CNS depression/toxicity — not recommended during treatment.
Opioids and other CNS depressants: increases somnolence/sedation, dizziness, and nausea; postmarketing reports describe life-threatening or fatal respiratory depression when combined with opioids, particularly in elderly patients.
Morphine: increases gabapentin/gabapentin enacarbil exposure and increases somnolence/dizziness/nausea.
Cimetidine: modest (~24%) increase in gabapentin AUC — not considered clinically significant.
No clinically meaningful interactions via major cytochrome P450 enzymes (gabapentin is not hepatically metabolized).

RLS trials (600 mg): somnolence/sedation (~20%), dizziness (~13%), headache; also fatigue and viral infection.
PHN trials (1,200 mg): dizziness (~17%), somnolence (~10%), headache (~10%).
Suicidal thoughts/behavior (class warning for antiepileptic drugs — pooled analyses showed roughly double the risk vs. placebo).
Respiratory depression when combined with opioids/CNS depressants (can be life-threatening).
DRESS syndrome/multiorgan hypersensitivity reactions (can be fatal, typically emerges within the first weeks of therapy); angioedema.
Driving/psychomotor impairment — counsel patients not to drive until they know how the drug affects them.
Withdrawal seizures with abrupt discontinuation; other withdrawal symptoms reported postmarketing include depression, suicidal ideation, agitation, confusion, anxiety, insomnia, nausea, tremor.
Peripheral edema, weight gain, blurred vision.
Depression and mood changes; dose-related.
Vertigo, incoordination.
Not associated with augmentation phenomenon or impulse control disorders (key differentiator from dopamine agonists).

Renal function (serum creatinine/CrCl) to guide dosing, both at baseline and periodically.
Mood, behavior, and suicidality.
Respiratory status and level of sedation, especially when co-prescribed with opioids or other CNS depressants.
Signs/symptoms of DRESS/hypersensitivity especially in the first several weeks of treatment.
Assess driving/psychomotor impairment.
Watch for withdrawal symptoms/seizures if stopped abruptly after chronic use.
For RLS: augmentation monitoring is not a primary concern, but ongoing efficacy and daytime sedation should be reassessed periodically.

Pregnancy: May cause fetal harm based on animal reproduction data; human data are limited. Late-pregnancy exposure carries a possible risk of neonatal withdrawal symptoms (tachypnea, hypertonia, irritability, feeding difficulty). Encourage enrollment in the NAAED Pregnancy Registry (1-888-233-2334).
Lactation: Gabapentin (the active metabolite) is excreted into human breast milk; monitor breastfed infants for somnolence, adequate weight gain, and feeding.