From the Guidelines
For a patient who took an additional 800mg dose of gabapentin (Neurontin), it is crucial to monitor for signs of central nervous system depression, including drowsiness, dizziness, and sedation, as these are the most common adverse effects associated with gabapentin overdose 1. Monitoring should also include watching for ataxia (unsteady gait), slurred speech, and confusion. Checking vital signs, particularly for respiratory depression in cases of significant overdose, is essential. Nystagmus (involuntary eye movements) and tremor may occur, and gastrointestinal symptoms like nausea or vomiting are possible. Given that gabapentin has a wide therapeutic window, most overdoses are relatively benign, especially at this dose level 1. However, an extra 800mg beyond the prescribed dose is unlikely to cause severe toxicity in most adults, though effects may be more pronounced in elderly patients or those with renal impairment since gabapentin is eliminated through the kidneys. Supportive care is typically sufficient, and symptoms generally resolve within 24-48 hours. If symptoms are severe or concerning, medical evaluation is warranted, particularly if the patient is on other CNS depressants like opioids or benzodiazepines, which can have dangerous synergistic effects with gabapentin. Key points to monitor include:
- Central nervous system depression signs (drowsiness, dizziness, sedation)
- Ataxia
- Slurred speech
- Confusion
- Vital signs, especially respiratory rate
- Nystagmus
- Tremor
- Gastrointestinal symptoms (nausea, vomiting) It's also important to consider the patient's renal function, as gabapentin dosage adjustments are necessary in patients with renal insufficiency 1.
From the FDA Drug Label
Overdosage A lethal dose of gabapentin was not identified in mice and rats receiving single oral doses as high as 8000 mg/kg. Signs of acute toxicity in animals included ataxia, labored breathing, ptosis, sedation, hypoactivity, or excitation. Acute oral overdoses of gabapentin up to 49 grams have been reported In these cases, double vision, slurred speech, drowsiness, lethargy, and diarrhea were observed. The patient should be monitored for signs of acute toxicity, including:
- ataxia
- labored breathing
- ptosis
- sedation
- hypoactivity
- excitation
- double vision
- slurred speech
- drowsiness
- lethargy
- diarrhea 2
From the Research
Monitoring Parameters
When a patient takes an additional 800mg dose of gabapentin, several parameters should be monitored due to the potential for overdose and adverse effects. These include:
- Vital signs: Close monitoring of vital signs such as blood pressure, heart rate, and respiratory rate is essential, as gabapentin overdose can lead to respiratory depression, hypotension, and other cardiovascular complications 3.
- Neurological status: The patient's neurological status should be closely monitored for signs of altered mental status, somnolence, dizziness, ataxia, and other neurological symptoms that may indicate gabapentin toxicity 4, 5, 3.
- Renal function: Gabapentin is excreted unchanged in urine, and its clearance is directly proportional to creatinine clearance. Therefore, patients with renal impairment may be at higher risk of gabapentin accumulation and toxicity. Monitoring renal function and adjusting the dose accordingly is crucial 4.
- Gabapentin levels: Measuring gabapentin levels can help assess the severity of the overdose and guide treatment. A postmortem peripheral blood gabapentin concentration of 88 μg/mL has been reported in a case of fatal gabapentin overdose 5.
- Opioid-related death risk: If the patient is also taking opioids, the risk of opioid-related death may be increased, especially with moderate to high doses of gabapentin. Close monitoring and adjustment of opioid doses may be necessary 6.
Potential Complications
Potential complications of gabapentin overdose include:
- Respiratory depression: Gabapentin can cause respiratory depression, especially when used in combination with other central nervous system depressants 3, 6.
- Cardiovascular complications: Gabapentin overdose can lead to hypotension, bradycardia, and other cardiovascular complications 3.
- Neurological symptoms: Gabapentin toxicity can cause a range of neurological symptoms, including somnolence, dizziness, ataxia, and altered mental status 4, 5, 3.
- Increased risk of opioid-related death: Concomitant use of gabapentin and opioids may increase the risk of opioid-related death, especially with moderate to high doses of gabapentin 6.