Phenobarbital: uses, dosing, side effects & brands

Phenobarbital is a medicine sold in the U.S. under one brand, for febrile seizures, partial epilepsies and tonic-clonic epilepsy. Below: what the FDA label says, every product that contains it, what the pills look like, and its recall record.

By the pharmaranks editorial teamReviewed against the FDA (openFDA label, NDC Directory & Enforcement) sourcesUpdated Jul 24, 2026How we research

Key facts

Treats: Febrile Seizures, Partial Epilepsies and Tonic-Clonic Epilepsy
Available as: Injectable
Sold as: Sezaby
Prescription?: Prescription only
Generic available?: Not in our catalog
What the pharmacy pays: about $3 for a 30-count supply — not your price
Boxed warning: Boxed warning

How phenobarbital is dosed

From the FDA label for Sezaby (application NDA215910). Other phenobarbital products — different forms, different strengths — are dosed differently. Follow the label for the one you were prescribed.

Loading Dose: 20 mg/kg is administered by intravenous infusion over 15 minutes into a large peripheral vein. If clinically indicated, at least 15 minutes after completion of the initial loading dose, a second loading dose may be administered over the subsequent 15 minutes as 20 mg/kg for term infants or 10 mg/kg or 20 mg/kg for preterm infants. The maximum total loading dose is 40 mg/kg. (2.1) Maintenance Dosage: starting 8 to 12 hours after first loading dose: 4.5 mg/kg/day given in 2 or 3 divided doses (i.e., 1.5 mg/kg every 8 hours or 2.25 mg/kg every 12 hours) up to 5 days. (2.1). Must be reconstituted with 10 mL 0.9 % Sodium Chloride Injection, USP prior to administration. See additional preparation and administration instructions in the Full Prescribing Information. (2.3) 2.1 Recommended Dosage and Administration The recommended dosage of SEZABY in neonates consists of a loading dose(s) followed by maintenance dosage (see Table 1). Administer SEZABY by intravenous infusion (over 15 minutes) into a large peripheral vein to avoid local tissue toxicity [see Warnings and Precautions (5.9)]. SEZABY is for intravenous use only. Table 1: Recommended Dosage of SEZABY for Neonatal Seizures Loading Dose (maximum total loading dose is 40 mg/kg) First loading dose 20 mg/kg Second loading dose (If clinically indicated) 1 Preterm Infants 10 mg/kg or 20 mg/kg [see Clinical Pharmacology…

Phenobarbital side effects

The following clinically significant adverse reactions are described elsewhere in the labeling: Risks from Concomitant Use with Opioids [see Warnings and Precautions (5.1)] Dependence and Withdrawal Reactions After Use of SEZABY for a Longer Duration Than Recommended [see Warnings and Precautions (5.2)] Abuse, Misuse, and Addiction with Unapproved Use in Adolescents and Adults [see Warnings and Precautions (5.3)] Respiratory Depression or Insufficiency [see Warnings and Precautions (5.4)] Serious Dermatologic Reactions [see Warnings and Precautions (5.5)] Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity [see Warnings and Precautions (5.6)] Hypersensitivity [see Warnings and Precautions (5.7)] Exacerbation of Porphyria [see Warnings and Precautions (5.8)] Injection Site Reactions [see Warnings and Precautions (5.9)] QT Prolongation [see Warnings and Precautions (5.10)] Embryofetal Toxicity with Unapproved Use in Adolescents and Adults [see Warnings and Precautions (5.11)] Neonatal Adverse Reactions from Unapproved Maternal Phenobarbital Use [see Warnings and Precautions (5.12)] Sedation, Respiratory Depression, and Withdrawal in Neonates Exposed to Phenobarbital Through Breast Milk [see Warnings and Precautions (5.13)] Suicidal Behavior and Ideation with Unapproved use in Adolescents and Adults [see Warnings and Precautions (5.14)] The…

Who shouldn’t take phenobarbital

SEZABY is contraindicated in patients with: acute porphyrias [see Warnings and Precautions (5.8)], or a history of hypersensitivity reaction to phenobarbital or other barbiturates [see Warnings and Precautions (5.7)] Acute porphyrias (4) Hypersensitivity to phenobarbital or other barbiturates (4)

Phenobarbital drug interactions

Inhibitors: Closely monitor and decrease SEZABY dosage, if needed. (7.1) CYP3A4, 2B6, 2C, UGT Substrates: Substrate dosage adjustment may be needed. (7.1) CNS depressants: Closely monitor for sedation and respiratory depression. (7.2) Drugs that Prolong the QT Interval : Avoid concomitant use. (7.3) 7.1 Cytochrome P450- or Uridine 5’-diphospho-glucuronosyltransferase (UGT)-Based Interactions The drug interaction information in Table 3 is based upon published literature in non-neonatal populations, in vitro studies, and the mechanistic knowledge of phenobarbital metabolic pathways [see Clinical Pharmacology (12.3)] . Although the data from the published literature regarding these drug interactions are from non-neonatal populations and the magnitude of the potential drug interactions in neonates have not been characterized, this information still warrants consideration given the potential impact of these possible drug interactions on the safety and efficacy of phenobarbital and CYP2B6, 2C9, 2C19, or UGT substrates in neonates. Table 3: Drug Interactions with SEZABY Effects of Other Drugs on SEZABY CYP2C9, 2C19, 2E1, Uridine 5'-diphospho-glucuronosyltransferases ( UGT) Inhibitors or Inducers Prevention or Management Closely monitor for adverse reactions (e.g., over sedation, prolonged QTc interval, etc.) when used concomitantly with inhibitors of these enzymes and reduced efficacy (e.g., breakthrough seizure) when used with inducers of these enzymes. Consider titration of the SEZABY maintenance dosage accordingly if concomitant use is unavoidable. Clinical Effect(s) Phenobarbital is a substrate of CYP2C9, CYP2C19, CYP2E1, and UGTs [see Clinical Pharmacology (12.3)] . It is likely that concomitant use will result in an increase in phenobarbital exposure when used with these inhibitors and a reduction when used with these inducers, which may increase the risk of SEZABY adverse reactions or reduce efficacy, respectively when concomitant use in neonates. Effects of Other Drugs on Sezaby CYP3A, 2B6, 2C(s), UGTs Substrates Prevention or Management Closely monitor neonates when SEZABY is used concurrently with substrates of these enzymes and consider increasing the dosage of the substrate accordingly, unless otherwise advised in its Prescribing Information, if concomitant use is unavoidable. Clinical Effect(s) Phenobarbital is an inducer of CYP3A, CYP2B6, CYP2C(s), and UGT(s) [see Clinical Pharmacology (12.3)] . It is likely that concomitant use in neonates will result in a decrease in the exposure of these substrates, which may reduce efficacy. 7.2 CNS Depressants Closely monitor for signs of sedation and respiratory depression with concomitant use of SEZABY with other CNS depressants, including opioids [see Warnings and Precautions (5.1)] . Phenobarbital may cause sedation and respiratory depression [see Warnings and Precautions (5.4) and Adverse Reactions (6.1)] . Other products that may also cause these adverse reactions may have additive pharmacologic effect and may increase the risk of sedation and respiratory depression. 7.3 Drugs that Prolong QT Interval SEZABY may prolong the QT interval [see Warnings and Precautions (5.10) and Clinical Pharmacology (12.2)] . Other products that may also prolong the QTc interval may have additive effects, and products that may increase concentrations of phenobarbital [see Drug Interactions (7.1)] may increase the QT prolongation risk; therefore, avoid concomitant use of SEZABY and these products. If concomitant use of a product that also prolongs the QTc interval or that increases SEZABY concentrations is unavoidable, monitor patients for increased risk of QTc interval prolongation.

Every phenobarbital product we track (1)

Same active ingredient — different manufacturer, form, price and FDA recall record. That last one is what our independent score measures.

Only one: Sezaby.

How long phenobarbital keeps

No phenobarbital label we read sets a separate limit for after opening, but they do specify how it must be stored — and the stability behind any date assumes those conditions.

Does phenobarbital expire? The in-use limits and storage rules from its labels

Phenobarbital and breastfeeding

From LactMed, the US National Library of Medicine’s Drugs and Lactation Database — quoted, not rewritten.

Inter- and intrapatient variability in excretion of phenobarbital into breastmilk is extensive. Phenobarbital in breastmilk apparently can decrease withdrawal symptoms in infants who were exposed in utero, but it can also cause drowsiness in some infants, especially when used with other sedating drugs. Monitor the infant for sedation, poor feeding and poor weight gain, especially in younger, exclusively breastfed infants and when using combinations of psychotropic drugs. Sometimes breastfeeding might have to be limited or discontinued because of excessive drowsiness and poor weight gain. If there is concern, measurement of the infant's serum phenobarbital concentration might help rule out toxicity.

Full LactMed record for phenobarbital: levels in milk, effects in breastfed infants, and the drugs it would consider instead

National Institute of Child Health and Human Development, record revised September 15, 2024. LactMed states its information is not a substitute for professional judgement.

What people report to the FDA about phenobarbital

The FDA Adverse Event Reporting System (FAERS) collects reports from patients and clinicians. It holds 585 reports naming phenobarbital, and the FDA flagged 96% of those reports as serious. The effects reported most often — leaving out reports about overdose, misuse or the condition being treated, which dominate the raw list for common medicines:

seizure80 reports
epilepsy38 reports
status epilepticus24 reports
pyrexia22 reports
fall21 reports
multiple-drug resistance20 reports
pallor19 reports
sepsis19 reports

Read these as a signal, not a rate. A report does not mean phenobarbital caused the effect — anyone can file one, and many describe people taking several medicines for several conditions. Crucially there is no denominator: FAERS does not record how many people took the drug, so these counts cannot be turned into “X% of patients” — a bigger number often just means a more widely used or more talked-about drug. Duplicates exist, and publicity drives reporting. For what is actually established, read the FDA label section above.

Source: openFDA drug/event (FAERS), retrieved July 25, 2026.

Related calculators

How long it stays in your system →

Frequently asked questions

What is phenobarbital?

Sezaby (Phenobarbital Sodium) is a medication used to treat Febrile Seizures, Partial Epilepsies, Tonic-Clonic Epilepsy, Hyperbilirubinemia.

Can you take phenobarbital with other medicines?

It depends on the medicine. We check it against the FDA labels rather than guessing: our interaction checker searches each drug's own label for the other and quotes what it says, naming the section it came from. Run phenobarbital against whatever else you take — and remember that a label not naming a drug is not the same as that combination being safe.

What forms does phenobarbital come in?

Across the brands we track, phenobarbital is currently marketed as injectable, per the FDA's National Drug Code Directory. Each form is dosed differently — follow the label for the exact product you were prescribed.

Is there a generic phenobarbital?

We do not currently list a generic-labelled phenobarbital product. That does not always mean none exists — it means none appears under a generic name in the FDA data we track. Ask your pharmacist.

How long does phenobarbital stay in your system?

Phenobarbital is a long-acting barbiturate with an elimination half-life of roughly 53–118 hours (about 2–5 days) in adults per the FDA label—one of the longest of any common sedative. Because of this, it can be detectable in blood and urine for about 2–3 weeks after the last dose, and longer with chronic high-dose use. In urine, standard barbiturate screens typically pick it up for around 1–3 weeks. Ranges are approximate and depend on dose, duration, age, and kidney/liver function. This is general information, not medical or legal advice.

Does phenobarbital show up on a drug test?

Yes. Phenobarbital is detected by the barbiturate portion of urine drug immunoassays and by confirmatory GC-MS or LC-MS/MS, and because of its long half-life it stays positive far longer than short-acting barbiturates. Clinicians also measure blood phenobarbital levels directly for therapeutic drug monitoring in epilepsy. If you take it by prescription, disclose that to the testing lab or medical review officer so a positive barbiturate result is interpreted correctly. Detection times vary by person; this is not medical or legal advice.

Cite this page

APA: pharmaranks. (2026, July 24). Phenobarbital: uses, dosing, side effects & brands. https://pharmaranks.com/drugs/phenobarbital
MLA: “Phenobarbital: uses, dosing, side effects & brands.” pharmaranks, 24 July 2026, https://pharmaranks.com/drugs/phenobarbital.

We summarise public FDA and NIH sources — for a clinical claim, cite the primary source we link to as well.

Sources: FDA openFDA drug label, National Drug Code Directory, and Enforcement (recall) database. This page reproduces public FDA data and is not medical advice. Dosing is set by your prescriber.

Read the full FDA label for phenobarbital on DailyMed (NIH) ↗ — including its boxed warning in full.