Drug reference

Gabapentin

Antiepileptic

Also known as Neurontin, Gabapin, Gralise, Horizant, Gabapentin Enacarbil

START

Confirm neuropathic pain diagnosis or seizure type. Baseline renal function. Start 300 mg PO at bedtime (reduce daytime somnolence). Titrate every 3-7 days.

TYPICAL MAX

1800 mg/day (PHN — demonstrated efficacy ceiling); 3600 mg/day (seizures — absolute max with diminishing returns)

STOP IF

Suicidal ideation, severe hypersensitivity (SJS/TEN/DRESS), respiratory depression, intolerable somnolence/ataxia, lack of efficacy after 4-6 weeks at 1800 mg/day

WATCH

Renal function (dose adjustment critical), suicidal ideation (mood changes), peripheral edema (weight, limb circumference), cognitive function in elderly, drug-seeking behavior (abuse potential)

CDSCO approvedSchedule HJan AushadhiATC N03AX12

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 45min · absorption onset
PEAK: 3h · 2-4 h (oral Cmax)
t½: 6h · 5-7 h (normal); prolonged in renal impairment
DURATION: 8h · 8 h (requires TID dosing)

EXCRETION

100% renal unchanged; zero hepatic metabolism

route + CYP

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

FDA PLLR: Limited human data. Animal studies showed developmental toxicity at high doses. May cause fetal harm. Use only if benefit outweighs risk. Pregnancy exposure registry available. Increased risk of cardiac defects with multiple administrations; late exposure linked to preterm birth and NICU admission.

FDA category + note

Top interactionssee all 12 →

AlcoholSevereDatabase
AlfentanilSevereDatabaseDDInter
BenzhydrocodoneSevereDatabaseDDInter
Benzodiazepines (e.g., Alprazolam, Clonazepam, Lorazepam)SevereDatabase

Available in India

259 branded formulations and 1,083 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Jan Aushadhi — generic available at GoI pharmacies

Mechanism

Gabapentin is a structural analog of gamma-aminobutyric acid (GABA) but does not bind to GABA-A or GABA-B receptors, nor does it influence GABA synthesis or metabolism. Its primary mechanism is binding with high affinity to the alpha-2-delta-1 (α2δ-1) auxiliary subunit of voltage-gated P/Q-type calcium channels in the central nervous system. This binding inhibits calcium influx and reduces the release of excitatory neurotransmitters (glutamate, norepinephrine, substance P) from presynaptic terminals, producing anticonvulsant, analgesic, and anxiolytic effects.

Indications

Postherpetic neuralgia (PHN)Adjunctive therapy for partial-onset seizures (with/without secondary generalization) in adults and children ≥3 yearsRestless legs syndrome (RLS) — gabapentin enacarbil formulationNeuropathic pain (diabetic neuropathy, peripheral neuropathy — off-label but widely used)Fibromyalgia (off-label)Anxiety disorders (off-label, including social anxiety)Alcohol withdrawal (off-label)Vasomotor symptoms (hot flashes) in menopause (off-label)

Dosing

Adult: Postherpetic neuralgia: Day 1: 300 mg PO; Day 2: 600 mg/day (300 mg BID); Day 3: 900 mg/day (300 mg TID). Titrate to 1800 mg/day (600 mg TID) as needed; max 3600 mg/day. Seizures (adjunctive): 300 mg TID initially; titrate to 900-1800 mg/day (max 3600 mg/day). RLS (enacarbil): 600 mg PO daily at 5 PM.
Pediatric: Partial seizures (≥3 years): 10-15 mg/kg/day initially, divided TID; titrate over 3 days to 25-35 mg/kg/day (max 50 mg/kg/day). Children 3-4 years: effective dose 40 mg/kg/day to match adult plasma levels.
Renal adjustment: CrCl 30-59: 200-700 mg BID. CrCl 16-29: 200-700 mg once daily. CrCl 15: 100-300 mg once daily. CrCl <15 (HD): 125-350 mg after each dialysis session. RLS (enacarbil): CrCl 30-59: 300 mg daily; CrCl 15-29: 100 mg daily; <15 on HD: 100 mg after dialysis.
Hepatic adjustment: No dosage adjustment required; not metabolized by the liver. AASLD recognizes gabapentin as preferred non-opioid analgesic in cirrhosis.
Geriatric: Start at low end of dosing range (300 mg/day); titrate slowly. Monitor for somnolence, dizziness, ataxia. Adjust for renal function.
Max dose: 1800 mg/day (PHN, demonstrated efficacy); 3600 mg/day (seizures, absolute max)

Pharmacokinetics

Onset

Analgesic effect: 1-2 weeks for neuropathic pain. Anticonvulsant: within days of reaching therapeutic dose.

Peak effect

Oral: peak plasma at 2-4 hours. Food increases Cmax by 14% and AUC slightly.

Duration

Dose-dependent; requires TID dosing for sustained effect due to short half-life.

Half-life

5-7 hours (adults); 4.7 hours (pediatrics); prolonged in renal impairment.

Bioavailability

Dose-dependent saturation of absorption: 900 mg/day ~60%; 1200 mg/day ~47%; 2400 mg/day ~34%; 3600 mg/day ~33%; 4800 mg/day ~27%. Non-linear pharmacokinetics due to saturable intestinal transport (LAT1 amino acid transporter).

Protein binding

<3% (negligible; not bound to plasma proteins).

Metabolism

Not appreciably metabolized in humans (<1% of dose metabolized; no active metabolites).

Excretion

Primarily renal: 100% excreted unchanged in urine via glomerular filtration.

Contraindications

Hypersensitivity to gabapentin or any component of the formulation
Gabapentin enacarbil: severe renal impairment (CrCl <15 mL/min) not on dialysis
No other absolute contraindications

Side effects

Common

Somnolence, dizziness, fatiguePeripheral edemaAtaxia, tremorHeadacheNausea, vomitingWeight gainVisual disturbances (diplopia, nystagmus)Xerostomia (dry mouth)

Serious

Suicidal ideation and behavior (FDA black box warning for all antiepileptic drugs)
Respiratory depression (especially with concurrent CNS depressants including opioids; FDA warning 2019)
Severe hypersensitivity reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, multi-organ failure)
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)
Acute pancreatitis (rare)
Rhabdomyolysis (rare)
Myoclonus (at high doses or rapid titration)
Reversible cognitive impairment (especially in elderly)

Pregnancy & lactation

Pregnancy

Lactation

Excreted in breast milk (infant serum levels ~10-15% of maternal). Generally considered compatible with breastfeeding. Monitor infant for drowsiness, poor feeding, adequate weight gain.

Drug interactions

Alcohol

Severe

Database

Increased risk of sedation, dizziness, impaired coordination, and respiratory depression.

Advise patients to avoid alcohol consumption while taking gabapentin.

Alfentanil

Severe

Database

Drug interaction classified as: absorption.

Source: DDInter

Benzhydrocodone

Severe

Database

Drug interaction classified as: synergy

Source: DDInter

Benzodiazepines (e.g., Alprazolam, Clonazepam, Lorazepam)

Severe

Database

Increased risk of sedation, dizziness, respiratory depression, and impaired psychomotor function.

Avoid concomitant use if possible. If co-administration is necessary, use the lowest effective doses and shortest duration possible. Monitor patients closely for signs of respiratory depression and sedation.

Buprenorphine

Severe

Database

Drug interaction classified as: synergy.

Source: DDInter

Butorphanol

Severe

Database

Drug interaction classified as: absorption.

Source: DDInter

Codeine

Severe