GABAPENTIN ENACARBIL
Clinical safety rating: safe
Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.
Gabapentin enacarbil is a prodrug of gabapentin. It binds to the α2δ subunit of voltage-gated calcium channels, inhibiting calcium influx and reducing release of excitatory neurotransmitters such as glutamate, norepinephrine, and substance P. This modulates neuronal excitability and pain transmission.
| Metabolism | Converted to gabapentin by non-specific esterases in the gastrointestinal tract and liver. Gabapentin is not appreciably metabolized in humans; it is eliminated renally unchanged. |
| Excretion | Renal: 100% as unchanged gabapentin (prodrug is rapidly hydrolyzed to gabapentin after absorption). No biliary or fecal elimination of active drug. |
| Half-life | Terminal half-life of gabapentin: 5–7 hours in patients with normal renal function. Renal impairment prolongs half-life proportionally to creatinine clearance decline. |
| Protein binding | Less than 3% bound to plasma proteins (negligible binding). |
| Volume of Distribution | Vd approximately 0.6–0.8 L/kg (around 50–60 L in adults), indicating distribution into total body water with minimal tissue binding. |
| Bioavailability | Oral bioavailability of gabapentin from gabapentin enacarbil: approximately 68% (fed) to 74% (fasted). Absolute bioavailability compared to oral gabapentin is enhanced due to active transport via monocarboxylate transporter type 1 (MCT-1). |
| Onset of Action | Oral: Peak serum concentrations occur at approximately 1 hour; clinical analgesic effect begins within 1–2 hours. No other routes approved. |
| Duration of Action | Analgesic effect: 6–8 hours, consistent with dosing three times daily. Duration correlates with serum half-life and therapeutic concentration maintenance. |
| Molecular Weight | 467.53 |
Initial: 600 mg orally once daily; titrate to 600 mg three times daily; max 2400 mg/day divided three times daily.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | CrCl >=60 mL/min: 600 mg three times daily; CrCl 30-59: 300 mg twice daily; CrCl 15-29: 300 mg once daily; CrCl <15: 300 mg every other day; hemodialysis: 300 mg after each dialysis. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A/B). For severe impairment (Child-Pugh C), reduce dose by 50% or extend dosing interval. |
| Pediatric use | Approved for partial-onset seizures in patients >=1 month; weight-based dosing: 10-15 mg/kg/day divided three times daily, titrate over 3 days to 30-40 mg/kg/day; max 50 mg/kg/day. |
| Geriatric use | Initiate at lower dose (e.g., 300 mg daily) and titrate slowly due to age-related renal impairment; monitor for sedation and dizziness. |
| 1st trimester | Risk of major congenital malformations unclear. Exposure associated with small increased risk of cardiac defects. Avoid unless benefit outweighs risk. |
| 2nd trimester | Limited data; consider risk of fetal harm. Use only if clearly needed. |
| 3rd trimester | Neonatal withdrawal syndrome (irritability, feeding difficulties) reported with late exposure. Avoid near term if possible. |
Clinical note
Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.
| FDA category | Animal |
| Placental transfer | Passes placenta; cord blood concentrations similar to maternal plasma. Animal studies show transplacental passage. |
| Breastfeeding |
■ FDA Black Box Warning
No FDA boxed warning.
| Common Effects | Viral infection Sleepiness Dizziness Impaired coordination Fatigue Fever |
| Serious Effects |
Hypersensitivity to gabapentin enacarbil or any component of the formulation
| Precautions | CNS depression (dizziness, somnolence) – impair ability to drive/operate machinery, Suicidal behavior and ideation, Respiratory depression, especially with concomitant CNS depressants or in patients with respiratory risk factors, Increased risk of adverse reactions with renal impairment; dose adjustment required, Abrupt discontinuation may precipitate withdrawal symptoms, Anaphylaxis and angioedema, Drug reaction with eosinophilia and systemic symptoms (DRESS) |
| Food/Dietary | No significant food interactions. However, high-fat meals may decrease the rate of absorption but not the extent. Take with or without food consistently. |
Loading safety data…
| Excreted into breast milk in low concentrations. Infant serum levels are very low; adverse effects unlikely. Monitor infant for drowsiness, poor feeding. Generally considered compatible with breastfeeding. |
| Lactation Rating | L2 (Possibly Compatible) |
| Teratogenic Risk | Animal studies show increased fetal malformations at clinically relevant doses. Human data: insufficient, but gabapentin (active metabolite) has been associated with increased risk of major congenital malformations (RR 1.2-1.4) and neurodevelopmental disorders. First trimester: avoid unless benefit outweighs risk. Second/third trimester: use lowest effective dose; monitor fetal growth. Late third trimester: risk of neonatal withdrawal (irritability, feeding difficulties). |
| Fetal Monitoring | Monitor maternal renal function, drug levels if efficacy concerns. Fetal ultrasound for growth and anatomy. Neonatal observation for withdrawal symptoms if used near term. |
| Fertility Effects | No clinical studies on fertility impact. Animal studies: no significant effects on fertility or reproductive performance. |
| Clinical Pearls | Gabapentin enacarbil is a prodrug of gabapentin with improved oral bioavailability (~75% vs 30-60% for gabapentin) and a longer dosing interval (twice daily vs three times daily). It is primarily indicated for restless legs syndrome (RLS) and postherpetic neuralgia (PHN). Dose adjustment is required in renal impairment (CrCl <60 mL/min). Avoid sudden discontinuation to prevent withdrawal symptoms. It may cause somnolence and dizziness; caution with concurrent CNS depressants. No significant drug interactions with antacids or food. |
| Patient Advice | Take gabapentin enacarbil exactly as prescribed, usually twice daily with or without food. · Do not crush or chew extended-release tablets; swallow whole with water. · Avoid driving or operating heavy machinery until you know how this medication affects you, as it may cause drowsiness or dizziness. · Do not stop taking this medication abruptly; taper under medical supervision to prevent withdrawal symptoms (e.g., anxiety, insomnia, nausea). · Inform your healthcare provider if you have kidney disease, are pregnant or breastfeeding, or take other sedating medications. · Common side effects include dizziness, sleepiness, and headache. Contact your doctor if you experience suicidal thoughts, unusual mood changes, or severe allergic reaction (rash, hives, swelling). · Store at room temperature away from moisture and heat. |