What is the treatment for phenobarbital poisoning?

Treatment of Phenobarbital Poisoning

Phenobarbital poisoning requires immediate supportive care with airway protection and hemodynamic stabilization, followed by multiple-dose activated charcoal (MDAC) as first-line enhanced elimination therapy, with extracorporeal treatment (ECTR) reserved for severe cases meeting specific clinical criteria. 1

Immediate Supportive Care (First Priority)

Airway and respiratory management:

• Intubate and provide mechanical ventilation for any patient exhibiting respiratory depression, as death from phenobarbital overdose most commonly results from respiratory depression leading to aspiration pneumonia 2, 1
• Monitor for Cheyne-Stokes respiration, areflexia, and progressive CNS depression 3
• Patients with chronic obstructive pulmonary disease are particularly vulnerable to respiratory depression even at lower concentrations 2

Hemodynamic stabilization:

• Administer aggressive fluid resuscitation for hypotension and shock, as cardiovascular depression occurs when medullary vasomotor centers are suppressed 2, 1
• Patients with congestive heart failure are more susceptible to cardiovascular collapse 2
• Vasopressor support (e.g., noradrenaline) may be required in severe cases with circulatory collapse 4

Monitoring requirements:

• Obtain serum phenobarbital concentration immediately (therapeutic range: 10-25 mg/L; coma-inducing: >50 mg/L; potentially fatal: >80 mg/L) 2, 1
• Perform urine drug screen and blood ethanol level to identify co-ingestions 2
• Continuous vital sign monitoring, including temperature (hypothermia expected) 3

Enhanced Elimination: Multiple-Dose Activated Charcoal

MDAC is the first-line enhanced elimination therapy and should be used in all significant phenobarbital poisoning cases 2, 1:

• Administer 15-20 g orally every 6 hours 2, 1
• Only administer after airway protection is secured to prevent aspiration, as gastric emptying is delayed in barbiturate toxicity 2, 1
• Continue MDAC even if ECTR is initiated, as the combination provides greater barbiturate removal than either alone 2, 1

Important caveat: Patients are at increased risk of gut impaction and perforation with MDAC due to delayed gastric emptying 2

Extracorporeal Treatment (ECTR): Indications for Severe Cases

ECTR should be initiated when ANY of the following criteria are met 2, 1:

Strong indications (Level 1D recommendations):

• Prolonged coma present or expected 2, 1
• Shock persisting after fluid resuscitation 2, 1
• Toxicity persists despite MDAC treatment 2, 1

Moderate indications (Level 2D recommendations):

• Serum phenobarbital concentration rises or remains elevated despite MDAC 2, 1
• Respiratory depression requiring mechanical ventilation 2, 1

Timing and duration:

• Initiate ECTR as soon as technically possible, ideally within 24 hours of exposure 2, 1
• Continue until clinical improvement is apparent 1
• Hemoperfusion reduces phenobarbital half-life by 78-88% compared to endogenous elimination 5

Choice of ECTR modality:

• Continuous renal replacement therapy (CRRT) is preferred for hemodynamically unstable patients 4
• Hemodialysis or hemoperfusion through activated charcoal are effective alternatives 3, 5
• Peritoneal dialysis is significantly less effective and not recommended 3

What NOT to Do

Urinary alkalinization is NOT recommended as first-line therapy because it does not significantly increase renal clearance compared to MDAC 2, 1

Do NOT base ECTR decisions solely on:

• Ingested dose estimates (often inaccurate) 2
• Serum concentrations alone (not reliable predictors of toxicity duration or severity) 2, 1
• However, concentrations >100 mg/L typically correlate with indications for ECTR 2

Analeptic agents are NOT recommended 3

Special Considerations

High-risk populations requiring closer monitoring:

• Chronic lung disease patients (more susceptible to respiratory depression) 2, 1
• Heart failure patients (more vulnerable to cardiovascular effects) 2, 1
• Co-ingestion with alcohol, opiates, or other CNS depressants creates additive life-threatening effects 1

Supportive measures during prolonged coma:

• Roll patient side-to-side every 30 minutes to prevent hypostatic pneumonia and decubiti 3
• Administer antibiotics if pneumonia is suspected 3
• Monitor for complications including pulmonary edema, cardiac arrhythmias, and renal failure 3

Clinical pitfall: Even with "flat" EEG suggesting brain death, this effect is fully reversible unless hypoxic damage has occurred—do not prematurely withdraw care 3