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Barbiturate anticonvulsant · For Cats

Luminal dosage reference for cats (Phenobarbital)

This page's standard weight-based reference is 2 mg per kg (0.91 mg per lb), with every 12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your cat's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset
15-30 minutes (acute), 1-2 weeks for steady-state levels
Duration
12 hours per dose
Class
Barbiturate anticonvulsant

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Phenobarbital (often known by brand names such as Luminal and Solfoton) is a barbiturate anticonvulsant commonly used in veterinary medicine for seizures, epilepsy, status epilepticus prevention, and seizure disorder management. Understanding the correct dosage, administration, and potential side effects of Phenobarbital is critical for your cat’s safety and well-being.

A typical Phenobarbital dose for cats is around 2 mg/kg every 12 hours, within a usual range of 1-3 mg/kg. Available forms include tablet, liquid, and injectable.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Phenobarbital Dosage Calculator for Cats

Enter your cat’s weight below to estimate the Phenobarbital dose from the 2 mg/kg guideline. Your veterinarian may adjust it for your cat’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your cat's weight

Quick Dosage Chart

Typical Phenobarbital amounts for common cat weights, for quick reference:

Dosage Chart · 02

Luminal weight-based reference chart for cats

Scroll sideways to see full table

Weight Lower Reference Standard Reference Upper Reference Frequency
3 lbs (1.4 kg) 1.4 mg 2.8 mg 4.2 mg every 12 hours
4 lbs (1.8 kg) 1.8 mg 3.6 mg 5.4 mg every 12 hours
5 lbs (2.3 kg) 2.3 mg 4.6 mg 6.9 mg every 12 hours
6 lbs (2.7 kg) 2.7 mg 5.4 mg 8.1 mg every 12 hours
7 lbs (3.2 kg) 3.2 mg 6.4 mg 9.6 mg every 12 hours
8 lbs (3.6 kg) 3.6 mg 7.2 mg 10.8 mg every 12 hours
9 lbs (4.1 kg) 4.1 mg 8.2 mg 12.3 mg (15mg tablet) every 12 hours
10 lbs (4.5 kg) 4.5 mg 9.0 mg 13.5 mg (15mg tablet) every 12 hours
12 lbs (5.4 kg) 5.4 mg 10.8 mg 16.2 mg (15mg tablet) every 12 hours
14 lbs (6.3 kg) 6.3 mg 12.6 mg (15mg tablet) 18.9 mg every 12 hours
16 lbs (7.3 kg) 7.3 mg 14.6 mg (15mg tablet) 21.9 mg every 12 hours
18 lbs (8.2 kg) 8.2 mg 16.4 mg (15mg tablet) 24.6 mg every 12 hours
20 lbs (9.1 kg) 9.1 mg 18.2 mg (15mg tablet) 27.3 mg (2 × 15mg) every 12 hours
25 lbs (11.3 kg) 11.3 mg (15mg tablet) 22.6 mg 33.9 mg every 12 hours

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Luminal reference by cat weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Phenobarbital to Your Cat

Give phenobarbital at the same times every day (every 12 hours) to maintain consistent blood levels. Tablets can be given with food to reduce stomach upset. Never skip doses or abruptly discontinue — this can trigger breakthrough seizures or status epilepticus, which is a medical emergency. If you miss a dose, give it as soon as possible and resume the regular schedule. A pill gun can help if your cat resists pilling.

It is generally recommended to give Phenobarbital with food to help reduce stomach upset. It may interact with chloramphenicol, cimetidine, other CNS depressants, corticosteroids, and cyclosporine.

Side Effects and Safety

Common side effects include sedation, increased appetite and weight gain, increased thirst and urination, and mild incoordination. More serious side effects can occur, such as liver toxicity (hepatotoxicity), bone marrow suppression, severe sedation, and paradoxical excitation.

Cautions · 12

When Luminal should be used with caution or avoided

Some cats should not take Luminal, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Luminal.

  • severe liver disease
  • severe anemia
  • known hypersensitivity
  • pregnancy

Interactions · 13

Luminal drug interactions

Luminal can interact with other drugs. This list is not complete — always give your veterinarian a full list of your cat's medications and supplements.

chloramphenicol
cimetidine
other CNS depressants
corticosteroids
cyclosporine

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult cat at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

  • In an emergency, or after accidental ingestion or a suspected overdose
  • For pregnant or nursing pets
  • For very young or very old cats
  • For pets with liver disease, kidney disease, or another chronic illness
  • For pets taking several medications at once
  • When you are not sure of your cat's current, accurate weight
  • For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your cat had too much Luminal, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

  • Call your veterinarian or the nearest emergency animal hospital.
  • ASPCA Animal Poison Control Center: (888) 426-4435
  • Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

Is phenobarbital safe for cats long term?
Phenobarbital can be used long-term in cats, but requires regular blood level monitoring (every 6 months) and liver function tests. Cats generally tolerate it well, though liver toxicity is the primary long-term concern. Your vet will adjust the dose based on blood phenobarbital levels and seizure control.
How often should phenobarbital blood levels be checked in cats?
Blood levels should be checked 2 weeks after starting or changing the dose, then every 6 months once stable. A complete blood count and liver panel should be run at least every 6-12 months to monitor for bone marrow and liver side effects.
What happens if I miss a dose of phenobarbital?
Missing a dose can lower blood levels enough to trigger a seizure, especially in cats with poorly controlled epilepsy. Give the missed dose as soon as you remember and resume the regular schedule. Never double the next dose. If your cat has a seizure after a missed dose, contact your vet immediately.
Can phenobarbital cure seizures in cats?
Phenobarbital does not cure seizures — it controls them by raising the seizure threshold in the brain. Most cats with epilepsy will need lifelong medication. The goal is to reduce seizure frequency and severity. Some cats may eventually be weaned off under veterinary supervision if seizure-free for an extended period.
Will phenobarbital make my cat sleepy?
Sedation is the most common side effect when starting phenobarbital, but most cats develop tolerance to this effect within 1-2 weeks. If sedation persists beyond 2 weeks, your vet may adjust the dose. Increased appetite and thirst are also common long-term effects.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your cat's weight by the lower, standard, and upper mg/kg values recorded for Luminal. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses
seizures, epilepsy, status epilepticus prevention, seizure disorder management
Recorded forms
tablet, liquid, injectable
Reference timing
every 12 hours; onset 15-30 minutes (acute), 1-2 weeks for steady-state levels; duration 12 hours per dose

Individual checks a calculator cannot perform

  • Confirm the diagnosis and the reason this medication is being considered.
  • Match the exact product, concentration, route, and whether a tablet may be split.
  • Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
  • Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

severe liver disease; severe anemia; known hypersensitivity; pregnancy.

Recorded interactions

chloramphenicol; cimetidine; other CNS depressants; corticosteroids; cyclosporine.

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your cat's complete medication list before acting on a number.

For Dogs

Looking for Luminal dosage for dogs?

View the Luminal dosage chart and calculator for dogs.

Related · 08

Related medications for cats

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 2 mg per kg (0.91 mg per lb) of body weight, given every 12 hours. The calculator multiplies that basis by your cat's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner
Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status
Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review cats dosage data.

Safety · 10

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