Gabapentin (Gabateva, Neurontin)
- USES: Gabapentin is approved by the US Food and Drug Administration (FDA) for the treatment of partial seizures (with and without secondary generalization) and postherpetic neuralgia. Gabapentin is also used for the treatment of diabetic peripheral neuropathy, migraines, pain disorders, and various mood and movement disorders (non-FDA labeled indications). PHARMACOLOGY: Gabapentin is a highly lipophilic amino acid structurally similar to GABA, but does not bind GABA receptors or alter levels in the brain. Gabapentin’s mechanism of action is unclear. TOXICOLOGY: Although gabapentin’s mechanism of action is unclear, its sedating effects are likely secondary to its lipophilic configuration and structural similarity to the inhibitory neurotransmitter GABA. EPIDEMIOLOGY: Gabapentin overdose is uncommon and manifestations are usually not severe. MILD TO MODERATE TOXICITY: In mild to moderate overdose, patients may present with sedation, ataxia, slurred speech, nystagmus, movement disorders, and gastrointestinal upset. SEVERE TOXICITY: In more severe cases, patients may present with mild hypotension and profound central nervous system depression requiring intubation. ADVERSE EFFECTS: Following therapeutic use, sedation, ataxia, dizziness, fatigue, nystagmus, hypotension and hypertension have occurred. Leukopenia has also been described with therapeutic use. Rhabdomyolysis is a rare adverse effect.
Range of Toxicity:
- TOXICITY: Overdoses of 35 g or less have been associated with mild toxicity in adults. Doses of 40 g or more have been associated with moderate toxicity in adults. A woman ingested 90 g of immediate release gabapentin and developed only mild symptoms that did not require any clinical intervention. An adult ingested more than 100 g and recovered with supportive care. THERAPEUTIC DOSE: ADULT: 900 to 3600 mg in 3 divided doses daily. PEDIATRIC: 10 mg/kg to 40 mg/kg in 3 divided doses daily.
- Support: MANAGEMENT OF MILD TO MODERATE TOXICITY: Treatment of gabapentin exposure is largely supportive with mild/moderate symptoms. An observation period of 4 to 6 hours is reasonable. MANAGEMENT OF SEVERE TOXICITY: Treatment of gabapentin exposure is largely supportive in nature with careful attention to airway protection in severe cases. Hypotension is usually mild responding to intravenous fluid boluses. If hypotension persists, administer dopamine or norepinephrine. Admit all severely symptomatic patients. Treat seizures with IV benzodiazepines or barbiturates.
- Decontamination: PREHOSPITAL: Prehospital GI decontamination is generally not necessary. HOSPITAL: Activated charcoal may be utilized to limit adsorption in patients with large, recent ingestions; however, risk of aspiration should be considered prior to administration.
- Airway management: In severely ill patients, airway management is paramount.
- Antidote: None. In one case report, flumazenil was effectively used to treat gabapentin-induced coma in a hemodialysis-dependent man with end-stage renal disease.
- Rhabdomyolysis: Administer sufficient 0.9% saline to maintain urine output of 2 to 3 mL/kg/hr. Monitor input and output, serum electrolytes, CK, and renal function. Diuretics may be necessary to maintain urine output. Urinary alkalinization is NOT routinely recommended.
- Monitoring of patient: Gabapentin serum concentrations are not readily available or useful in guiding therapy. Basic laboratory studies along with acetaminophen and salicylate levels can be ordered for severely symptomatic or self-harm patients. No studies are required for minimally symptomatic patients who have not attempted self-harm. Monitor mental status and vital signs in symptomatic patients. Monitor CK, renal function, and urine output in patients with rhabdomyolysis.
- Enhanced elimination procedure: Gabapentin can be removed by hemodialysis; it has a small volume of distribution and minimal protein binding. However, as toxicity is generally mild, hemodialysis is rarely indicated. Hemodialysis may be useful in patients with renal insufficiency who are severely symptomatic.
- Patient disposition: HOME CRITERIA: Patients with inadvertent ingestions who are not symptomatic may be observed at home with telephone follow up. OBSERVATION CRITERIA: Observe all patients who are symptomatic for 4 to 6 hours. When patients are asymptomatic they may be discharged home. ADMISSION CRITERIA: Admit all moderately to severely symptomatic patients, especially if there is a concern for falls, inability to care for self, or risk of worsening central nervous system depression. CONSULT CRITERIA: Involve a toxicologist with any questions or concerns.