What is the management approach for phenobarbital (barbiturate) poisoning?

Management of Phenobarbital (Barbiturate) Poisoning

Optimal supportive care with airway protection is mandatory in all cases, followed by multiple-dose activated charcoal (MDAC) after airway security, and extracorporeal treatment (ECTR) reserved only for severe cases with prolonged coma, shock, or persistent toxicity despite MDAC. 1

Immediate Supportive Care (First Priority)

Airway and respiratory management takes absolute precedence:

• Intubate and provide mechanical ventilation for any patient exhibiting respiratory depression, as death from phenobarbital overdose most commonly results from aspiration pneumonia secondary to respiratory depression 2, 1
• Barbiturates suppress the medullary respiratory center, and patients with underlying COPD are particularly vulnerable even at therapeutic doses 2

Hemodynamic stabilization is critical:

• Administer aggressive fluid resuscitation for hypotension and shock, as cardiovascular depression occurs when medullary vasomotor centers are suppressed 2, 1
• Cardiac vascular tone and contractility become compromised at higher doses, potentially causing hypotension that can reduce cardiac output and decrease ECTR effectiveness if needed 2
• Monitor continuously for typical shock syndrome including apnea, circulatory collapse, and respiratory arrest 3

Obtain diagnostic studies:

• Measure serum phenobarbital concentration (therapeutic range: 10-25 mg/L; coma-inducing: >50 mg/L; potentially fatal: >80 mg/L) 2, 1
• Perform simultaneous urine drug screen and blood ethanol concentration to identify co-ingested drugs, particularly other CNS depressants like alcohol, opiates, or benzodiazepines which create additive life-threatening effects 2, 1

Enhanced Elimination: Multiple-Dose Activated Charcoal

MDAC is the first-line enhanced elimination method for all significant phenobarbital poisoning:

• Administer 15-20 g orally every 6 hours, but only after the airway is secured to prevent aspiration 2, 1
• Gastric emptying decreases during barbiturate toxicity, increasing risks of gut impaction, perforation, and aspiration 2
• MDAC provides superior elimination compared to urinary alkalinization, which is no longer recommended as it does not significantly increase renal clearance 2, 1

Extracorporeal Treatment: Reserved for Severe Cases Only

ECTR should be initiated for patients meeting specific criteria:

• Prolonged coma despite MDAC treatment 1
• Shock or hemodynamic instability requiring vasopressor support 1, 4
• Persistent toxicity despite optimal supportive care and MDAC 1

Technical considerations for ECTR:

• Initiate as soon as technically possible, ideally within 24 hours of exposure 1
• Continue MDAC concurrently with ECTR for maximal barbiturate removal 1
• Continue ECTR until clinical improvement is apparent, not based solely on serum levels 1
• For hemodynamically unstable patients, continuous renal replacement therapy (CRRT) may be preferred over intermittent hemodialysis 4

Important caveat: Serum concentrations confirm poisoning diagnosis but are not reliable predictors of toxicity duration or severity—clinical status should guide ECTR decisions 2, 1

High-Risk Populations Requiring Heightened Vigilance

• COPD patients: More susceptible to respiratory depression even at doses considered therapeutic in healthy individuals 2, 1
• Heart failure patients: More vulnerable to cardiovascular depression and hypotension 2, 1
• Polysubstance ingestion: Co-ingestion with other CNS depressants creates additive effects making overdose far more dangerous 2, 1
• Chronic barbiturate users: Tolerance to sedative-hypnotic effects develops, but tolerance to lethal respiratory failure does not; these patients tolerate higher doses but not higher serum concentrations before lethal toxicity risk 2

Common Pitfalls to Avoid

Do not use urinary alkalinization as monotherapy—it is inferior to MDAC for enhancing phenobarbital elimination 2, 1

Do not administer MDAC before securing the airway—the decreased gastric emptying and altered mental status create unacceptable aspiration risk 2, 1

Do not rely solely on serum levels to guide management—clinical parameters (respiratory status, hemodynamics, level of consciousness) should drive treatment decisions 2, 1

Do not use analeptic agents—these are not recommended in barbiturate overdose management 3

Monitoring and Supportive Measures

• 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 pneumonia, pulmonary edema, cardiac arrhythmias, congestive heart failure, and renal failure 3
• Consider hypoglycemia, head trauma, cerebrovascular accidents, convulsive states, and diabetic coma in differential diagnosis 3