Phenobarbital
LUMINAL
Pronunciation: fee-noe-BAR-bi-tal
“Fear no barbed ’Luminati”
Shredder inDucer
What it isBarbiturate GABA-A modulator; seizures, neonatal seizures and alcohol withdrawal.
Why it mattersCheap, available worldwide, and still first-line for neonatal seizures.
What it changesSedation, dependence, and it is one of the strongest enzyme inducers in the pharmacopoeia, so co-prescribed drugs fail.
Phenobarbital prescription history
Animated chart of estimated U.S. prescriptions per year, Antiseizure meds (1869–2026). Phenobarbital enters in 1913 (estimated).
FDA-approved for
- seizures (~1912)
Off-label
- alcohol withdrawal
Principal riskSedation, dependence, and strong enzyme induction
Classes and tags
Clinical profile
Legacy pregnancy categoryD
Defining liabilityRespiratory depression, dependence and strong enzyme induction; overdose can cause prolonged coma.
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Sedation (daytime) | Adult | 30-120 mg/day divided BID-TID | 400 mg/day | |
| Hypnotic | Adult | 100-200 mg QHS | ||
| Anticonvulsant | Adult | 60-200 mg/day | ||
| Anticonvulsant | Pediatric | 3-6 mg/kg/day |
Renal Undefined
Hepatic Contraindicated in marked hepatic impairment
No more than 400 mg in any 24-hour period.
Instructions
- Reduce dose in elderly or debilitated patients
- Avoid abrupt withdrawal (risk of withdrawal seizures)
- Pediatric anticonvulsant loading dose 15-20 mg/kg produces ~20 mcg/mL levels
Available strengths
- tab 15, 16.2, 30, 32.4, 60, 64.8, 97.2, 100 mg
- sol 60 mg/15 mL
- sol 20 mg/5 mL
- sol 30 mg/7.5 mL
- inj 65, 130 mg/mL
Contraindications
- History of manifest or latent porphyria
- Marked impairment of liver function
- Respiratory disease with evident dyspnea or obstruction
Cautions
- CNS and respiratory depression, apnea
- Dependence and withdrawal seizures with abrupt discontinuation
- Paradoxical excitement in elderly/children; restlessness/delirium if given with pain
- Pregnancy Category D
Adverse reactions
- Residual sedation/hangover, drowsiness, lethargy, vertigo
- Respiratory depression, apnea, circulatory collapse
- Paradoxical excitement; irritability/hyperactivity in children
- Hypersensitivity reactions (rarely exfoliative dermatitis)
Pregnancy Category D; in-utero exposure risks neonatal withdrawal (seizures, hyperirritability).
Lactation Undefined
Cost
| Strength | #/mo | generic $/mo | CostPlus | |
|---|---|---|---|---|
| 15 mg | tab | 60 BID | $4.60 | not offered |
| 16.2 mg | tab | 60 BID | $3.35 | not offered |
| 30 mg | tab | 60 BID | $8.50 | not offered |
| 32.4 mg | tab | 60 BID | $4.71 | not offered |
| 60 mg | tab | 60 BID | $10.85 | not offered |
| 64.8 mg | tab | 60 BID | $6.10 | not offered |
| 97.2 mg | tab | 60 BID | $7.06 | not offered |
| 100 mg | tab | 60 BID | $12.76 | not offered |
Generic entryBy 2023
Open Phenobarbital in the interactive console ↗
Memory aids: interaction avatars
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Self-check
- Phenobarbital: Which neonatal indication remains first-line?
Neonatal seizures. - Phenobarbital: Why can co-prescribed drugs fail?
Strong enzyme induction.