What effect does gabapentin (anticonvulsant medication) have on blood pressure in cases of overdose, specifically regarding the risk of hypotension?

Gabapentin Overdose and Blood Pressure Effects

Gabapentin overdose can cause hypotension, though this is not a consistent or prominent feature and occurs primarily in cases of massive overdose or when combined with other sedating medications. 1, 2

Blood Pressure Effects in Gabapentin Overdose

Hypotension Risk Profile

• Hypotension is documented but uncommon in isolated gabapentin overdose, appearing in approximately 2 of 13 symptomatic patients in one case series 3
• Massive overdoses are more likely to cause hypotension: A case report documented hypotension with a serum gabapentin concentration of 104.5 μg/mL (the highest recorded level), which also required mechanical ventilation 2
• The FDA label for gabapentin mentions hypotension specifically in the context of anaphylaxis and angioedema, not as a direct toxic effect of overdose 1

Clinical Presentation of Overdose

The predominant effects of gabapentin overdose are neurological rather than cardiovascular 1, 3:

• Central nervous system depression is the hallmark: drowsiness, lethargy, somnolence, and sedation 1, 3
• Ataxia, slurred speech, and dizziness are common 1, 3
• Double vision and diarrhea may occur 1
• Coma and respiratory depression occur only in massive overdoses, particularly in patients with renal impairment 1, 2

Factors That Increase Hypotension Risk

Concomitant use with other sedating medications significantly amplifies cardiovascular risk 4, 2:

• Combined overuse of gabapentin and opioids quadruples the odds of drug-related hospitalization and increases risk of respiratory depression and altered mental status 4
• Co-ingestion with quetiapine (which independently causes hypotension and QTc prolongation) resulted in severe hypotension requiring intervention 2

Renal impairment dramatically increases toxicity risk 5:

• Gabapentin elimination half-life increases from 5-9 hours to 132 hours in dialysis patients 5
• Patients on dialysis have increased risk of altered mental status, falls, and fractures when taking gabapentin 5
• Dose adjustment is critical: plasma clearance is directly proportional to creatinine clearance 5

Management Approach

Immediate Assessment

Focus on airway protection and respiratory status rather than blood pressure as the primary concern 1:

• Monitor for CNS depression: somnolence, sedation, respiratory depression 1
• Check renal function immediately: creatinine clearance determines elimination capacity 5
• Identify co-ingestions: particularly opioids, benzodiazepines, or antipsychotics that potentiate effects 4, 2

Treatment Strategy

Supportive care is the mainstay 1:

• Hemodialysis is indicated for severe overdose, particularly in patients with renal impairment or coma 1
• Gabapentin can be removed by hemodialysis, making it the definitive treatment for life-threatening overdose 1
• Monitor vital signs continuously for at least 10 hours, as clinical effects typically resolve within this timeframe in most cases 3

Key Clinical Pitfall

Do not assume gabapentin is benign in overdose simply because therapeutic doses are well-tolerated 6:

• A fatal case has been documented with postmortem gabapentin concentration of 88 μg/mL in a 62-year-old woman with depression 6
• Doses up to 49 grams have been survived with supportive care alone 1
• The unpredictability of severe toxicity warrants close monitoring even when initial presentation appears mild 6, 2