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PetDosageChart

Luminal (Phenobarbital) Dosage for Cats

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

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator

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Luminal Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 1.5mg 3mg 4mg every 12 hours
4 lbs (1.8 kg) 2mg 3.5mg 5.5mg every 12 hours
5 lbs (2.3 kg) 2.5mg 4.5mg 7mg every 12 hours
6 lbs (2.7 kg) 2.5mg 5.5mg 8mg every 12 hours
7 lbs (3.2 kg) 3mg 6.5mg 9.5mg every 12 hours
8 lbs (3.6 kg) 3.5mg 7mg 11mg every 12 hours
9 lbs (4.1 kg) 4mg 8mg 12.5mg (15mg tablet) every 12 hours
10 lbs (4.5 kg) 4.5mg 9mg 13.5mg (15mg tablet) every 12 hours
12 lbs (5.4 kg) 5.5mg 11mg 16mg (15mg tablet) every 12 hours
14 lbs (6.3 kg) 6.5mg 12.5mg (15mg tablet) 19mg every 12 hours
16 lbs (7.3 kg) 7.5mg 14.5mg (15mg tablet) 22mg every 12 hours
18 lbs (8.2 kg) 8mg 16.5mg (15mg tablet) 24.5mg every 12 hours
20 lbs (9.1 kg) 9mg 18mg (15mg tablet) 27.5mg (2 × 15mg) every 12 hours
25 lbs (11.3 kg) 11.5mg (15mg tablet) 22.5mg 34mg every 12 hours

What is Luminal (Phenobarbital) used for in cats?

seizures epilepsy status epilepticus prevention seizure disorder management

How to give Luminal 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.

Available Forms

tablet, liquid, injectable

Give with Food?

Yes — give with food

Side effects of Luminal in cats

Common side effects

sedation
increased appetite and weight gain
increased thirst and urination
mild incoordination

Serious side effects

  • liver toxicity (hepatotoxicity)
  • bone marrow suppression
  • severe sedation
  • paradoxical excitation

When to call the vet

Call your vet immediately if your cat shows any of these signs:

  • Seizure lasting more than 5 minutes or cluster seizures
  • Yellowing of gums or skin (liver damage)
  • Severe lethargy or inability to walk
  • Loss of appetite for more than 24 hours
  • Unexplained bruising or bleeding

Related Medications for Cats

Anticonvulsant / Analgesic

Neurontin

Gabapentin

For pain management

View dosage chart
Antihistamine

Benadryl

Diphenhydramine

For allergies

View dosage chart
NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart
H2 receptor antagonist

Pepcid

Famotidine

For stomach acid reduction

View dosage chart

Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Phenobarbital.

Frequently Asked Questions

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.

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