GABAPENTIN ENACARBIL

Clinical safety rating: safe

Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.

How it works

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.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.

FDA category	Animal
Breastfeeding	Gabapentin excreted into breast milk; M/P ratio approximately 1.0. Infant serum levels <12% maternal therapeutic levels. Monitor infant for sedation, poor feeding. Use with caution; benefits of breastfeeding may outweigh risks.
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).

Warnings & precautions

■ FDA Black Box Warning

No FDA boxed warning.

Side Effect Profile

Common Effects	Viral infection Sleepiness Dizziness Impaired coordination Fatigue Fever
Serious Effects

Absolute Contraindications

["Hypersensitivity to gabapentin enacarbil, gabapentin, or any component of the formulation"]

Clinical Precautions

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)"]

Clinical Tips & Counseling

Drug interactions

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GABAPENTIN ENACARBIL

Clinical safety rating: safe

Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.

How it works

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Antacids decrease absorption May cause somnolence dizziness and respiratory depression especially with opioids.

FDA category	Animal
Breastfeeding	Gabapentin excreted into breast milk; M/P ratio approximately 1.0. Infant serum levels <12% maternal therapeutic levels. Monitor infant for sedation, poor feeding. Use with caution; benefits of breastfeeding may outweigh risks.
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).

Warnings & precautions

■ FDA Black Box Warning

No FDA boxed warning.

Side Effect Profile

Common Effects	Viral infection Sleepiness Dizziness Impaired coordination Fatigue Fever
Serious Effects

Absolute Contraindications

["Hypersensitivity to gabapentin enacarbil, gabapentin, or any component of the formulation"]