NEURONTIN
Clinical safety rating
cautionComprehensive clinical and safety monograph for NEURONTIN (NEURONTIN).
Gabapentin binds to the α2δ subunit of voltage-gated calcium channels, inhibiting calcium influx and reducing neurotransmitter release, particularly glutamate, norepinephrine, and substance P. It does not interact with GABA receptors.
| Metabolism | Gabapentin does not undergo hepatic metabolism; it is excreted unchanged in urine. No involvement of cytochrome P450 enzymes. |
| Excretion | Renal elimination as unchanged drug: >90%; 0.3% is excreted in feces; biliary elimination is negligible. |
| Half-life | Terminal elimination half-life is 5–7 hours in patients with normal renal function; in elderly or those with renal impairment, half-life may be prolonged up to 132 hours; requires dose adjustment for creatinine clearance <60 mL/min. |
| Protein binding | <3% bound to plasma proteins (negligible). |
| Volume of Distribution | Volume of distribution is 0.8 L/kg (57 L in a 70 kg adult), indicating distribution into total body water. |
| Bioavailability | Oral bioavailability is approximately 60% (30–90% with interindividual variability); decreases with higher doses due to saturable absorption; not affected by food. |
| Onset of Action | Oral: Peak plasma concentrations occur 2–4 hours after dosing; clinical effect onset may be within 1–2 weeks for neuropathic pain and epilepsy. |
| Duration of Action | Duration of action is approximately 8–12 hours based on dosing interval (typically TID); steady-state achieved by 1–2 days. |
| Molecular Weight | 171.24 |
300 mg orally once daily on day 1, 300 mg twice daily on day 2, then 300 mg three times daily on day 3; titrate up to effective dose, usual maintenance 300-600 mg three times daily, maximum 3600 mg/day.
| Dosage form | CAPSULE |
| Renal impairment | For CrCl 30-59 mL/min: 200-700 mg twice daily. For CrCl 15-29 mL/min: 200-700 mg once daily. For CrCl <15 mL/min: 100-300 mg once daily. Hemodialysis: loading dose 300-400 mg, then 200-300 mg after each 4-hour dialysis session. |
| Liver impairment | No specific dose adjustment guidelines; pharmacokinetics unchanged in hepatic impairment per manufacturer. |
| Pediatric use | For epilepsy (ages 3-12): initial 10-15 mg/kg/day in 3 divided doses, titrate over 3 days to effective dose, maintenance 25-35 mg/kg/day in 3 divided doses; maximum 50 mg/kg/day. For postherpetic neuralgia: not indicated. |
| Geriatric use | Initiate at lower dose (e.g., 100-300 mg/day) and titrate slowly; monitor for dizziness, sedation, and renal function; adjust dose based on creatinine clearance. |
| 1st trimester | Gabapentin crosses the placenta. Data are insufficient to determine drug-associated risk of major birth defects or miscarriage. However, one study suggested a potential small increased risk of major malformations, particularly cardiac defects, with first-trimester exposure. |
| 2nd trimester | Limited data; potential for adverse effects such as low birth weight and preterm birth has been reported in some studies. Use only if clearly needed. |
| 3rd trimester | Third-trimester exposure may be associated with neonatal withdrawal syndrome and respiratory depression. Monitor neonate for signs of sedation, hypotonia, and difficulty feeding. |
Clinical note
Comprehensive clinical and safety monograph for NEURONTIN (NEURONTIN).
| Placental transfer | Gabapentin crosses the placenta; cord blood concentrations are approximately 1-2 times maternal plasma concentrations. Ratio of cord to maternal plasma is 1.0-2.0. |
| Breastfeeding | Gabapentin is excreted into breast milk in low to moderate amounts. Infant serum levels are low and no adverse effects have been reported in most cases. However, monitor infant for drowsiness, poor feeding, and weight gain. Preterm or compromised infants may be more susceptible. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | First trimester: Increased risk of major congenital malformations (e.g., neural tube defects, heart defects) based on epidemiological data; avoid use if possible. Second and third trimester: Risk of fetal growth restriction, preterm birth, and neonatal withdrawal symptoms (e.g., feeding difficulties, irritability) after in utero exposure. |
| Fetal Monitoring | Maternal: Therapeutic drug monitoring of gabapentin levels is not routinely recommended but may be considered if toxicity suspected. Monitor for signs of CNS depression, dizziness, and ataxia. Fetal/Neonatal: Ultrasound for fetal growth and anatomy, especially if first-trimester exposure. Newborn assessment for withdrawal symptoms for 48-72 hours post-delivery. |
| Fertility Effects | No significant adverse effects on fertility in animal studies. In humans, no conclusive evidence of impaired fertility; however, limited data exist. Gabapentin may affect reproductive hormones (e.g., decrease in testosterone) in males, but clinical significance unclear. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to gabapentin or any component of the formulation
| Precautions | Respiratory depression: risk increased with opioid coadministration or in elderly patients, Central nervous system effects: dizziness, somnolence, ataxia, Increased seizure frequency with abrupt withdrawal, Suicidal behavior and ideation, Anaphylaxis and angioedema, Drug reaction with eosinophilia and systemic symptoms (DRESS), Pancreatitis, Abrupt discontinuation may precipitate status epilepticus in patients with seizures |
| Food/Dietary | No significant food interactions. Avoid alcohol due to additive CNS depression. |
| Clinical Pearls | Titrate slowly to reduce CNS depression risk. Reduce dose in renal impairment (CrCl <60). Drug of choice for postherpetic neuralgia. Gabapentin is not effective for acute pain. Avoid abrupt discontinuation to prevent withdrawal. Use with caution with opioids due to respiratory depression risk. |
| Patient Advice | May cause dizziness and drowsiness; avoid driving until effects known. · Take with or without food; avoid alcohol. · Do not stop suddenly; taper under doctor guidance. · May take time to work; adhere to prescribed dosing schedule. · Report any signs of allergic reaction, mood changes, or suicidal thoughts. |
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