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Gabapentin enacarbil is an extended-release prodrug of the gabapentinoid gabapentin that is enzymatically hydrolyzed to gabapentin after absorption. It was engineered to overcome the erratic, saturable absorption of oral gabapentin by acting as a substrate for high-capacity nutrient transporters (MCT-1 and SMVT) expressed throughout the small and large intestine, yielding sustained, dose-proportional plasma gabapentin concentrations. Marketed as Horizant in the United States and Regnite in Japan, it is approved for moderate-to-severe primary restless legs syndrome (RLS, also called Willis-Ekbom disease) and for the management of postherpetic neuralgia. Like gabapentin, its active moiety binds the alpha-2-delta (a2d) auxiliary subunit of voltage-gated calcium channels rather than acting directly on GABA receptors, reducing depolarization-evoked release of excitatory neurotransmitters.
- Relieves moderate-to-severe restless legs syndrome symptoms (IRLS score reductions in RCTs)
- Smooth, dose-proportional gabapentin exposure with once-daily dosing
- Eases postherpetic neuralgia nerve pain
- Improves sleep quality and mood alongside RLS symptom relief
- No augmentation risk, unlike dopamine-agonist RLS therapies
- Calming, anxiolytic gabapentinoid feel
- Dizziness, especially in the first days of treatment
- Possible weight gain and peripheral edema
- Impairs driving and coordination; dangerous combined with alcohol or other CNS depressants
Overview
From the notes: gabapentin enacarbil is basically gabapentin that finally absorbs the way you want it to. Regular gabapentin gets soaked up by a saturable transporter, so plasma levels get flaky as you go up; enacarbil is a prodrug that rides high-capacity transporters spread along the whole gut, then cleaves to gabapentin once it is in, giving you smooth, dose-proportional levels and clean once-daily dosing.
For restless legs it is hands down one of the better tolerated options; in the PIVOT trials it pulled down IRLS scores, improved sleep and mood, and notably showed no augmentation, which is the big trap with the dopamine agonists. It carries the same calming, anxiolytic gabapentinoid feel people know from pregabalin. Honest note: this is a prescription drug, it will make you drowsy and a little wobbly early on, and you do not want to stack it with alcohol or other depressants or stop it cold turkey.
Mechanism
Gabapentin enacarbil is a transported : it is designed as a substrate for the monocarboxylate transporter MCT-1 (SLC16A1) and the sodium-dependent multivitamin transporter SMVT (SLC5A6), which are high-capacity and distributed throughout the intestine, so absorption is not saturated the way passive/amino-acid-transporter uptake of plain gabapentin is. After absorption it is rapidly hydrolyzed by non-specific esterases to release gabapentin (the active drug) plus inactive byproducts.
Gabapentin itself does not bind -A or GABA-B receptors despite the name; it binds with high affinity to the alpha-2-delta-1 (a2d-1, gene CACNA2D1) auxiliary subunit of presynaptic voltage-gated calcium channels (and to a lesser degree a2d-2). This binding reduces calcium influx through the channel and trafficking of the channel to the membrane, dampening depolarization-evoked release of excitatory neurotransmitters such as , noradrenaline, and substance P. In restless legs syndrome and neuropathic pain this translates to reduced sensory hyperexcitability. The extended-release format gives sustained, dose-proportional gabapentin exposure with a longer effective duration than immediate-release gabapentin.
receptor fingerprint
a2d-1 subunit of voltage-gated Ca2+ channels (CACNA2D1)Binds / inhibits (via active gabapentin)
MCT-1 transporter (SLC16A1)Substrate (absorption)
a2d-2 subunit of voltage-gated Ca2+ channels (CACNA2D2)Binds
SMVT transporter (SLC5A6)Substrate (absorption)
-A / GABA-B receptorsNo direct binding
Dosingtypical ranges, not medical advice
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Safetyrisks and cautions, not medical advice
Gabapentin enacarbil is a prescription drug; the most common adverse events across trials are somnolence/sedation and dizziness, usually mild-to-moderate and often transient. Weight gain, peripheral edema, and driving impairment can occur. Like all gabapentinoids it should not be combined with alcohol, opioids, or other CNS depressants (additive sedation and respiratory-depression risk) and should be tapered rather than stopped abruptly. Product labeling carries class warnings for suicidal thoughts/behavior and for possible driving impairment. Notably, RLS trials reported no augmentation and no QT-interval prolongation. Not risk-free, but generally well tolerated at the approved dose.
Interactionsdocumented pairs only, not exhaustive
Gabapentin enacarbil is a prodrug of gabapentin and does not undergo significant hepatic metabolism, instead relying on hydrolysis and renal elimination. In a randomized crossover study, gabapentin enacarbil showed no clinically significant pharmacokinetic interaction with morphine; when coadministered, the AUC and Cmax of both drugs remained within bioequivalent ranges (90% CI 0.8 to 1.25) [7]. However, a pharmacodynamic interaction was noted; patients receiving the combination reported slightly greater dizziness and somnolence than those on either drug alone, indicating additive central nervous system effects. The lack of hepatic metabolism for gabapentin enacarbil means interactions with CYP inhibitors or inducers are unlikely; formal studies of potential interactions with other drugs remain limited, and most coadministrations remain clinically unstudied.
Checking a whole stack? Run it through interactions + stacks.
Subjective profileweighing the evidence above
A well-engineered gabapentin prodrug that fixes the erratic absorption of plain gabapentin; a solid, non-augmenting option for moderate-to-severe restless legs syndrome and postherpetic neuralgia, with predictable once-daily kinetics and the usual gabapentinoid sedation to respect.
Resources
This entry is here for reference.
Research
- 2010first citedGabapentin enacarbil in restless legs syndrome
- 2017most recentGabapentin enacarbil, pregabalin and rotigotine are equally effective in restless legs syndrome…
- 1.Gabapentin Enacarbil: A Review in Restless Legs Syndrome
- 2.Efficacy of gabapentin enacarbil vs placebo in patients with postherpetic neuralgia and a pharmacokinetic comparison with oral gabapentin
- 3.Gabapentin enacarbil, pregabalin and rotigotine are equally effective in restless legs syndrome: a comparative meta-analysis
- 4.Gabapentin enacarbil: in patients with restless legs syndrome
- 5.Gabapentin enacarbil for the treatment of moderate to severe primary restless legs syndrome (Willis-Ekbom disease): 600 or 1,200 mg dose?
- 6.Gabapentin enacarbil in restless legs syndrome
- 7.Gabapentin enacarbil and morphine administered in combination versus alone: a double-blind, randomized, pharmacokinetic, and tolerability comparison.
7 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
What is gabapentin enacarbil used for?
It is FDA-approved for moderate-to-severe primary restless legs syndrome (Willis-Ekbom disease) and for managing postherpetic neuralgia (nerve pain after shingles). It is sold as Horizant in the US and Regnite in Japan.
How is it different from regular gabapentin?
Plain gabapentin relies on a saturable transporter, so absorption becomes unreliable at higher doses. Enacarbil is a prodrug absorbed by high-capacity transporters throughout the gut and then converted to gabapentin, giving smoother, dose-proportional blood levels and once-daily dosing.
Does it cause augmentation like dopamine agonists?
No. In the PIVOT RLS trials and pooled analyses there were no reports of augmentation (the paradoxical worsening seen with long-term dopamine agonists) and no QT-interval prolongation, which is a key advantage for long-term RLS management.
Is it well-researched?
Yes. It has multiple double-blind, placebo-controlled RCTs (including PIVOT RLS I and II and a postherpetic neuralgia trial), long-term maintenance and extension studies, and network meta-analyses placing it among the most effective RLS drugs alongside pregabalin and rotigotine.
What are the main side effects?
Somnolence/sedation and dizziness are by far the most common, usually mild and often fading with time. Weight gain, swelling, and impaired driving can occur; it should not be mixed with alcohol or other depressants and should be tapered, not stopped suddenly.
Adverse effects
- Dizziness, especially in the first days of treatment
- Possible weight gain and peripheral edema
- Impairs driving and coordination; dangerous combined with alcohol or other CNS depressants
Notes and cautions
- Somnolence and sedation are the most common effects
- Prescription drug with abuse potential and withdrawal risk if stopped abruptly