Benzodiazepines remain the guideline-supported first-line treatment for alcohol withdrawal syndrome (AWS) in the emergency department (ED).¹ For most patients, appropriately dosed benzodiazepines effectively control tremor, agitation, autonomic hyperactivity, and the risk of progression to seizures and delirium tremens. However, a subset of patients with severe alcohol withdrawal may have an inadequate clinical response despite escalating doses of benzodiazepines, a phenomenon often termed benzodiazepine-resistant or resistant alcohol withdrawal.²

Phenobarbital has consequently received renewed attention as an adjunct—and in some centers, an alternative—to benzodiazepines.³ Its pharmacology is attractive, its long duration of action is well suited to the time course of alcohol withdrawal, and observational data suggest potential benefits. However, enthusiasm for phenobarbital should be tempered by the limited high-quality evidence supporting its use. Only two small, randomized ED trials have directly evaluated phenobarbital in AWS, and the 2024 Guidelines for Reasonable and Appropriate Care in the Emergency Department (GRACE-4) guideline characterizes the certainty of evidence supporting adjunctive phenobarbital as low to very low.^1,3,4,5

Why Might Phenobarbital Work Better Than Benzodiazepines?

The pharmacologic rationale begins with the neurobiology of alcohol withdrawal. Gamma-aminobutyric acid (GABA) provides much of the brain’s inhibitory signaling, whereas glutamate provides excitatory signaling. Chronic alcohol exposure produces compensatory adaptations in both systems. When alcohol intake abruptly stops, reduced inhibitory activity combined with excessive excitatory activity produces the characteristic central nervous system hyperactivity of AWS.⁶

Benzodiazepines enhance GABA-mediated inhibition but do not directly suppress glutamatergic excitation. Phenobarbital acts on both sides of the equation: It enhances inhibitory activity at GABA-A receptors while reducing excitatory glutamatergic transmission.⁶ This dual mechanism provides a plausible pharmacologic rationale for phenobarbital in patients with severe withdrawal or an inadequate response to benzodiazepines.

Phenobarbital also has potentially advantageous pharmacokinetics. Its half-life ranges from about 50–140 hours, substantially longer than lorazepam and generally longer than diazepam. It is nearly 100 percent bioavailable by intravenous (IV), intramuscular, and oral routes and exhibits relatively predictable linear pharmacokinetics.^6,7

The long half-life effectively provides an “auto-taper.” Rather than the peaks and valleys that can occur between doses of shorter-acting benzodiazepines, phenobarbital provides sustained suppression of withdrawal symptoms after administration has stopped. With IV administration, peak clinical effect occurs at approximately 30 minutes, allowing reassessment and additional dosing at roughly 30-minute intervals.^8,9

The pharmacology is therefore compelling. The clinical evidence, as we will see, is considerably less definitive.

How Should Phenobarbital Be Dosed in the ED?

Two practical dosing strategies are commonly used: weight-based loading and incremental dosing.¹⁰

For a younger, otherwise robust patient with severe withdrawal, particularly one with previous withdrawal seizures or delirium tremens and minimal preceding benzodiazepine exposure, consider 6–10 mg/kg IV based on ideal body weight.^5,10 Ideal, rather than actual, body weight is important, particularly at extremes of body size.

An alternative is incremental dosing. Depending on age, frailty, comorbidities, previous sedative exposure, and withdrawal severity, consider 60–240 mg IV, followed by reassessment approximately 30 minutes later.^8,10 An older patient with concurrent medical illness and alcohol withdrawal, for example, might reasonably receive 60 or 120 mg initially rather than a large weight-based load.

Whichever strategy is selected, carefully track the cumulative dose. Many protocols use 20 mg/kg of ideal body weight as the maximum cumulative dose, although the optimal ceiling has not been established and clinicians should follow local protocols.

Large loading doses should not be given by rapid IV push. Appropriate dilution and infusion rates vary by institution, making this an appropriate medication for early involvement of the ED pharmacist.

Equally important is determining the clinical endpoint. Treatment should be titrated to the patient’s clinical response rather than simply to a numerical withdrawal score. When titrating phenobarbital, a reasonable clinical endpoint is resolution of agitation with the patient calm and alert or mildly drowsy but readily arousable to voice, corresponding approximately to a Richmond Agitation-Sedation Scale score of 0 to –1.^11,12  Resolution of tongue tremor provides another useful objective bedside sign.

After each dose, reassess level of consciousness, respiratory rate, oxygen saturation, hemodynamics, withdrawal signs, and cumulative sedative exposure.

Which Patients Are Most Likely to Benefit?

The optimal phenotype for phenobarbital has not been established. This remains an important evidence gap highlighted by the GRACE-4 guideline.¹ Studies have used widely differing definitions of moderate and severe withdrawal, phenobarbital eligibility, dosing regimens, and outcome measures.

In practice, phenobarbital is most compelling in appropriately monitored patients with moderate to severe AWS requiring admission, particularly those with previous complicated withdrawal, previous alcohol-withdrawal seizures, previous delirium tremens, recurrent intensive care unit (ICU) admissions for withdrawal, or an inadequate response to initial benzodiazepines.¹

Phenobarbital may also be useful when symptom-triggered benzodiazepine protocols are unreliable. Clinical Institute Withdrawal Assessment for Alcohol, Revised (CIWA-Ar) includes subjective measures and requires patient participation, limiting its utility in patients with delirium, cognitive impairment, language barriers, or severe illness.¹³ In these patients, objective clinical assessment with incremental phenobarbital dosing may be preferable to escalating benzodiazepines based on an unreliable CIWA-Ar score.

Once phenobarbital is selected, avoid independently escalating both phenobarbital and benzodiazepines. Simultaneously titrating two long-acting sedative strategies makes the patient’s response more difficult to interpret and increases the potential for cumulative sedation and respiratory depression.

Contraindications and drug interactions must also be considered. Acute intermittent porphyria and marked hepatic impairment are important contraindications. Phenobarbital is a potent hepatic enzyme inducer and may reduce concentrations of clinically important medications, including some antiretroviral agents, transplant immunosuppressants, direct oral anticoagulants, and methadone.¹⁴ The clinical importance of these interactions after limited phenobarbital exposure remains uncertain, and recommendations vary.

What Does the Evidence Actually Show?

Despite increasing use of phenobarbital for AWS, randomized ED evidence remains surprisingly sparse.

In 2011, Hendey et al. conducted a prospective randomized trial of 44 ED patients, comparing IV phenobarbital with lorazepam. Patients receiving phenobarbital received a mean dose of 509 mg, whereas those given lorazepam received a mean of only 4.2 mg. Both groups experienced significant improvement in withdrawal scores, with no significant differences in discharge withdrawal scores, ED length of stay, hospital admission, or withdrawal scores at 48-hour follow-up .⁴ The relatively small lorazepam doses and small sample size limit the conclusions that can be drawn from this study.

In 2013, Rosenson et al. performed a prospective randomized, double-blind, placebo-controlled study of 102 patients. All patients received a standardized symptom-guided lorazepam protocol and were randomized to receive either placebo or a single 10 mg/kg IV phenobarbital load. The addition of phenobarbital reduced ICU admissions, although secondary outcomes, including adverse events and hospital and ICU length of stay, were not significantly different.⁵

These are important studies, but 146 randomized patients across two trials is hardly definitive evidence for a medication increasingly incorporated into ED and ICU alcohol-withdrawal protocols. Most of the remaining literature consists of retrospective and observational studies with considerable heterogeneity in patient selection, disease severity, phenobarbital dosing, concomitant benzodiazepine use, and clinical setting.

The 2024 Society for Academic Emergency Medicine GRACE-4 guideline attempted to synthesize this heterogeneous literature using Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology.¹ For adults with moderate to severe AWS who are being admitted to hospital, the guideline suggests phenobarbital in addition to benzodiazepines rather than benzodiazepines alone. Importantly, this is a conditional recommendation based on low to very low certainty of evidence.

The combined direct and indirect literature suggests possible reductions in ICU admission, mechanical ventilation, hospital length of stay, and need for continuous sedative infusions. These signals are encouraging but should not be mistaken for definitive evidence of superiority.

Be Cautious About Discharge After Phenobarbital

One of the most important unresolved questions is whether patients can safely be discharged after receiving substantial doses of phenobarbital in the ED.

The same long half-life that makes phenobarbital attractive also creates potential risk. A patient discharged after a large IV load has pharmacologically active phenobarbital on board for days. Subsequent alcohol consumption or use of benzodiazepines, Z-drugs, opioids, or other sedatives could result in additive central nervous system and respiratory depression.

The available discharge literature is predominantly retrospective and heterogeneous, with substantial variation in withdrawal severity, phenobarbital dosing, patient selection, and clinician disposition decisions.³ Consequently, GRACE-4 could not recommend phenobarbital for patients intended for discharge from the ED.¹

Practice currently varies considerably: Some centers discharge selected patients after phenobarbital treatment, whereas others routinely admit them. Until better prospective safety data are available, caution is appropriate, particularly after large cumulative doses or in patients at risk for concurrent sedative use. Prescribing phenobarbital after discharge has even less support. Outpatient phenobarbital tapers should be avoided. No evidence supports this practice, and unsupervised phenobarbital use carries the potential for severe or fatal toxicity.

For now, benzodiazepines remain the standard first-line treatment for AWS. Phenobarbital is best viewed as an additional tool, particularly for selected patients with severe, complicated, or benzodiazepine-resistant withdrawal. Its pharmacology is appealing and the emerging clinical literature is encouraging, but the evidence is not sufficiently robust to justify indiscriminate use.

When phenobarbital is chosen, consider the patient’s age, comorbidities, withdrawal history, previous sedative exposure, and disposition; dose deliberately; reassess frequently; and track the cumulative dose. As with most ED resuscitation, the safest strategy is not a rigid protocol but thoughtful titration to the individual patient.

A special thank you to Dr. Zoe Polsky, the guest expert on the EM Cases podcast, who inspired this column.

Dr. Helman is an emergency physician at North York General Hospital in Toronto. He is an assistant professor in the division of emergency medicine at the University of Toronto, and the education innovation lead at the Schwartz/Reisman Emergency Medicine Institute. He is the founder and host of the Emergency Medicine Cases podcast and website.

References

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