Phenobarbital

Phenobarbital Seizure Medication for Dogs & Cats

Phenobarbital is an anticonvulsant medication used to reduce the frequency and severity of seizures in dogs and cats. While it’s unlikely to eliminate seizures completely, the goal is to make seizures less frequent and less severe.

Phenobarbital Dosing & Administration

Give phenobarbital on a consistent schedule, which is typically twice a day, with or without food. Set reminders so doses stay on track, since consistency matters for seizure control.

Missed doses & Changing medications

Phenobarbital is a seizure medication, so do not stop it suddenly.

If your pet misses a dose, give it as soon as you remember unless it’s close to the next scheduled dose time on the prescription label. If it’s close, skip the missed dose and give the next dose at the regular scheduled time. Do not give extra or double doses unless your pet’s veterinary team specifically instructs you to.

Talk with your veterinary team before making any changes to a phenobarbital plan. Seizure medications generally require tapering rather than stopping abruptly.

Monitoring & Lab work

Plan on regular veterinary visits while your pet takes phenobarbital. At a minimum, schedule visits twice yearly to comply with prescription regulations for controlled substances. Your veterinary team will also run initial liver function testing to confirm the medication is appropriate for your pet.

Phenobarbital level monitoring is important:

  • Check levels two weeks after starting phenobarbital or after a dose change

  • Recheck levels every six months thereafter

General blood work and liver tests are recommended annually. A bile acids test requires fasting and a two-hour clinic stay, so contact the team ahead of time if that timing overlaps with your pet’s medication schedule.

Potential Side effects of Phenobarbital

Many pets take phenobarbital with no side effects or only mild, tolerable effects. Contact your veterinary team if any side effect feels excessive or starts to interfere with quality of life.

Reported side effects include:

  • Sleepiness or “drunk” behavior: Some pets act sleepy or uncoordinated while adjusting. Adjustment can take about two weeks. Keep pets away from swimming pools and staircases if coordination is poor.

  • Increased thirst and urination: Do not restrict water intake during the day. If accidents happen overnight, pull up water after dinner, then offer a full bowl again in the morning.

  • Increased appetite: Monitor food intake. A diet food may help a pet feel satisfied while avoiding unwanted weight gain. Watch for inappropriate eating, since some dogs start eating toys or getting into the garbage.

  • Thyroid test interference in dogs: Phenobarbital can interfere with common thyroid testing. It doesn’t appear to cause hypothyroidism, but it can change blood test results. Discuss thyroid monitoring needs before starting phenobarbital.

  • Liver enzyme changes: Phenobarbital will likely increase liver enzymes, and rarely it can cause liver dysfunction. An increase in enzymes alone doesn’t mean there’s a liver problem, however. Other tests, such as a bile acids test, can help clarify whether liver changes are expected or indicate a concern.

  • Blood dyscrasias: Rarely, phenobarbital can cause changes in red and white blood cells. This can be dangerous, but stopping the medication usually reverses the effect.

  • Pancreatitis: Uncommonly, phenobarbital can contribute to pancreatitis. If your pet has chronic pancreatitis or starts vomiting after starting phenobarbital, contact your veterinary team.

  • Skin changes: Rarely, itching or skin lesions can occur. If redness, itching, or sores appear, contact your veterinary team.

Phenobarbital FAQs

  • Phenobarbital is an anticonvulsant medication used to reduce the frequency and severity of seizures. The goal is improved seizure control, although complete seizure freedom is unlikely.

  • Phenobarbital is typically given twice a day, with or without food. Give it on a consistent schedule.

  • If your pet misses a dose of phenobarbital, give it as soon as you remember unless it’s close to the next scheduled dose time on the prescription label. If it’s close, skip the missed dose and give the next dose at the regular scheduled time. Do not give extra or double doses unless your pet’s veterinary team specifically instructs you to.

  • Schedule at least twice-yearly visits to comply with controlled-substance prescription regulations. Your veterinary team will run initial liver testing, check phenobarbital levels two weeks after starting or a dose change, and recheck levels every six months. General blood work and liver tests are recommended annually.

  • Some pets act sleepy or uncoordinated while adjusting, and adjustment can take about two weeks. Increased thirst, increased urination, and increased appetite can also occur. Contact your veterinary team if side effects feel excessive or affect quality of life.