Gabapentin, sold under brand names like Neurontin and Gralise, is a medication primarily used to manage certain types of nerve pain, such as postherpetic neuralgia, and to control partial-onset seizures. The drug works by binding to specific subunits of voltage-gated calcium channels in the nervous system. This action reduces the release of excitatory neurotransmitters, dampening overactive nerve signaling and providing its therapeutic effect. Taking a dose significantly higher than prescribed amplifies these depressant effects, leading to acute dangers ranging from severe incapacitation to life-threatening medical emergencies.
Common Signs of Excessive Dosing
When a person takes a dose of gabapentin moderately higher than prescribed, the initial effects involve a marked increase in central nervous system (CNS) depression. The most frequent symptom is profound drowsiness, which can progress to extreme sedation, making the person difficult to arouse.
CNS depression severely impairs coordination and motor control. This often results in severe unsteadiness, known as ataxia, which causes significant difficulty walking or standing without falling. Speech musculature can also be affected, leading to slurred speech or difficulty articulating words clearly.
Eye movement disturbances, such as nystagmus, involve involuntary and repetitive eye movements. Severe dizziness or vertigo is common, often accompanied by double or blurred vision. Gastrointestinal upset, including nausea, vomiting, and diarrhea, has also been reported. These effects represent a significant risk for accidental injury, such as falls, even if the ingestion is not immediately fatal.
Severe Toxic Effects and Medical Emergencies
A significant gabapentin overdose, particularly when combined with other CNS depressants like opioids or alcohol, escalates the risk to life-threatening levels. The most concerning complication is respiratory depression, characterized by slow, shallow, or labored breathing. This occurs because the drug depresses the body’s drive to breathe, which can lead to hypoxia, oxygen deprivation, and potentially respiratory arrest.
Profound CNS depression can progress to a state of unarousable loss of consciousness or coma. Prolonged unconsciousness puts the patient at risk for secondary complications. One serious, though rare, complication is rhabdomyolysis, where damaged muscle tissue releases myoglobin into the bloodstream.
Myoglobin is toxic to the kidneys and can cause acute kidney injury. Since gabapentin is excreted unchanged by the kidneys, renal impairment can cause the drug to accumulate further in the body. While low blood pressure can occur, the primary dangers relate to airway management and secondary organ damage from immobility and kidney failure.
Immediate Response and Supportive Care
If signs of excessive gabapentin dosing are observed, such as severe drowsiness, slurred speech, or difficulty breathing, immediate action is necessary. The first step is to call emergency services or a Poison Control Center for guidance. Be prepared to state the amount of drug taken, the time of ingestion, and whether any other substances were consumed.
While awaiting medical help, monitor the person’s breathing and level of consciousness. Treatment for gabapentin overdose in a hospital setting is largely supportive, as there is no specific antidote. Staff focus on maintaining the patient’s airway and breathing, often involving supplemental oxygen or, for severe respiratory depression, intubation and mechanical ventilation.
Decontamination may include administering activated charcoal, which is most effective if given within one to two hours of ingestion. Charcoal works by binding the drug in the stomach and intestines, preventing further absorption. For patients with pre-existing kidney dysfunction or severe toxicity, hemodialysis may be used to actively remove the gabapentin from the blood.