Is Phenobarbital safe for dogs and cats?
Moderate risk for petsPhenobarbital is the first-line anticonvulsant for idiopathic epilepsy in dogs and is used long-term in the majority of epileptic dogs. It is an effective and generally well-tolerated drug at therapeutic plasma levels (20–40 μg/mL). Long-term hepatotoxicity is the primary veterinary safety concern: phenobarbital induces hepatic CYP450 enzymes and can cause hepatocellular injury, increased serum alkaline phosphatase (ALP) and alanine aminotransferase (ALT), and in some cases progresses to hepatic fibrosis and cirrhosis with chronic use. Regular liver enzyme monitoring (every 6 months) and periodic phenobarbital serum level measurement are standard of care. Idiosyncratic hepatotoxicity (rare but potentially severe) can occur at any dose. Polydipsia/polyuria, polyphagia, sedation, and ataxia are common at supratherapeutic levels. Abrupt discontinuation in dogs controlled on phenobarbital carries a high risk of status epilepticus and is contraindicated. Phenobarbital is a Schedule IV controlled substance in the US due to its potential for human abuse/dependence, which limits its availability relative to potassium bromide.
What is phenobarbital?
Also known as: Phenobarbitone, Luminal, Phenobarbitol, Fenobarbital.
- CAS number
- 50-06-6
- Molecular formula
- C12H12N2O3
- Molecular weight
- 232.23 g/mol
- SMILES
- CCC1(C(=O)NC(=O)NC1=O)C2=CC=CC=C2
- PubChem CID
- 4763
Risk for dogs
Moderate riskPhenobarbital is the first-line anticonvulsant for idiopathic epilepsy in dogs and is used long-term in the majority of epileptic dogs. It is an effective and generally well-tolerated drug at therapeutic plasma levels (20–40 μg/mL). Long-term hepatotoxicity is the primary veterinary safety concern: phenobarbital induces hepatic CYP450 enzymes and can cause hepatocellular injury, increased serum alkaline phosphatase (ALP) and alanine aminotransferase (ALT), and in some cases progresses to hepatic fibrosis and cirrhosis with chronic use. Regular liver enzyme monitoring (every 6 months) and periodic phenobarbital serum level measurement are standard of care. Idiosyncratic hepatotoxicity (rare but potentially severe) can occur at any dose. Polydipsia/polyuria, polyphagia, sedation, and ataxia are common at supratherapeutic levels. Abrupt discontinuation in dogs controlled on phenobarbital carries a high risk of status epilepticus and is contraindicated. Phenobarbital is a Schedule IV controlled substance in the US due to its potential for human abuse/dependence, which limits its availability relative to potassium bromide.
Risk for cats
Moderate riskPhenobarbital is the most commonly used anticonvulsant in cats, as its safety profile is more favorable in this species compared to diazepam (associated with fulminant hepatic necrosis in cats) or potassium bromide (causes eosinophilic bronchopneumopathy in cats). Therapeutic plasma levels for cats are typically 20–40 μg/mL, similar to dogs. Hepatotoxicity monitoring is still required but the risk profile in cats is considered somewhat lower than in dogs for chronic hepatotoxicity. Sedation, ataxia, and polyphagia occur at supratherapeutic levels. Phenobarbital is generally well-tolerated for long-term seizure management in cats under veterinary supervision with appropriate monitoring. Accidental overdose — from cats accessing owners' pill organizers or phenobarbital bottles — produces deep sedation, respiratory depression, hypothermia, and CNS depression; these are veterinary emergencies requiring supportive care.
Regulatory consensus
1 regulatory bodyhas classified Phenobarbital.
| Agency | Year | Classification | Notes |
|---|---|---|---|
| DEA | — | Schedule IV | Controlled substance classification |
Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.
Where pets encounter phenobarbital
- Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
- Occupational Environments — Factories, Warehouses, Transportation vehicles
Safer alternatives
Lower-risk approaches that achieve a similar outcome to Phenobarbital:
-
Alternative drug class; Non-pharmacological therapy; Lowest effective dose
Trade-offs: Direct chemical substitution requires verification that the replacement does not introduce new hazards (regrettable substitution). Conduct full hazard assessment of proposed alternative before adoption.Relative cost: 1.2-2×
Frequently asked questions
Is phenobarbital safe for pets?
Phenobarbital is the first-line anticonvulsant for idiopathic epilepsy in dogs and is used long-term in the majority of epileptic dogs. It is an effective and generally well-tolerated drug at therapeutic plasma levels (20–40 μg/mL). Long-term hepatotoxicity is the primary veterinary safety concern: phenobarbital induces hepatic CYP450 enzymes and can cause hepatocellular injury, increased serum alkaline phosphatase (ALP) and alanine aminotransferase (ALT), and in some cases progresses to hepatic fibrosis and cirrhosis with chronic use. Regular liver enzyme monitoring (every 6 months) and periodic phenobarbital serum level measurement are standard of care. Idiosyncratic hepatotoxicity (rare but potentially severe) can occur at any dose. Polydipsia/polyuria, polyphagia, sedation, and ataxia are common at supratherapeutic levels. Abrupt discontinuation in dogs controlled on phenobarbital carries a high risk of status epilepticus and is contraindicated. Phenobarbital is a Schedule IV controlled substance in the US due to its potential for human abuse/dependence, which limits its availability relative to potassium bromide.
What products contain phenobarbital?
Phenobarbital appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments).
See Phenobarbital in the pets app
Look up products containing phenobarbital, compare to alternatives, and explore the full data record.
Open in pets View raw API dataSources (3)
- US FDA: Phenobarbital Prescribing Information — Indications, Adverse Effects, Dependence, Drug Interactions, and Controlled Substance Status (Schedule IV) (2019) — regulatory
- ASPCA Animal Poison Control Center: Phenobarbital Toxicosis in Dogs and Cats — Accidental Overdose, CNS Depression, and Management (2023) — veterinary
- Plumb's Veterinary Drug Handbook (10th ed.) — Phenobarbital: Anticonvulsant Use in Dogs and Cats, Hepatotoxicity Monitoring, and Dosing (2023) — veterinary
Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →