Phenobarbital vs Keppra (levetiracetam) for dog seizures
Phenobarbital is the long-standing, inexpensive first choice for epilepsy in dogs but needs blood tests to watch levels and the liver. Levetiracetam (Keppra) has fewer side effects and little effect on the liver, but it is given more often and is frequently used as an add-on.
Updated October 4, 2026
At a glance
- How often
- Phenobarbital
- Usually twice a day
- Levetiracetam
- Three times a day, or twice a day for extended-release
- Monitoring
- Phenobarbital
- Blood levels and liver tests
- Levetiracetam
- Little routine monitoring
- Common side effects
- Phenobarbital
- Sleepiness, thirst, hunger, weight gain
- Levetiracetam
- Mild sleepiness or wobbliness
- Liver
- Phenobarbital
- Can affect the liver with long-term use
- Levetiracetam
- Little effect on the liver
- Controlled substance
- Phenobarbital
- Yes
- Levetiracetam
- No
Phenobarbital | Levetiracetam Keppra | |
|---|---|---|
| How often | Usually twice a day | Three times a day, or twice a day for extended-release |
| Monitoring | Blood levels and liver tests | Little routine monitoring |
| Common side effects | Sleepiness, thirst, hunger, weight gain | Mild sleepiness or wobbliness |
| Liver | Can affect the liver with long-term use | Little effect on the liver |
| Controlled substance | Yes | No |
Where each fits
Phenobarbital controls seizures well in many dogs, costs little, and has decades of use behind it, so it is often the first medicine. Levetiracetam is chosen when liver concerns rule phenobarbital out, when side effects are a problem, or as an add-on when one medicine is not enough. Potassium bromide and zonisamide are other options your vet may discuss.
Phenobarbital in practice
Dogs often seem sleepy, wobbly, hungry and thirsty for the first couple of weeks, which usually eases. Your vet checks blood levels to find the right dose and liver tests over time, because long-term use can strain the liver. It is a controlled substance, so refills follow controlled-medicine rules.
Levetiracetam in practice
Levetiracetam leaves the body quickly, so standard tablets are given about every eight hours; extended-release tablets allow twice-daily dosing but must be swallowed whole, never split or crushed. Side effects are usually mild.
Never stop suddenly
Stopping any seizure medicine abruptly can trigger severe seizures, including clusters. Give doses on time, refill before you run out, and change doses only with your vet. Seizures lasting more than five minutes, or several in a row, are an emergency.
Getting them filled
Both are human medicines that a regular pharmacy can fill with your vet’s prescription, which often lowers the price. Keep a seizure diary to help your vet judge how well treatment is working.
Questions for your vet
- Which medicine suits my dog’s liver and seizure pattern?
- How often will blood tests be needed?
- What should I do during a long seizure or a cluster?
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Sources
Written by the Script Unlock editorial team from the sources above. It is general information, not advice for you or your pet; your vet decides which medicine is right.
Script Unlock is a marketplace that lets licensed pharmacies quote a cash price on your prescription. It does not prescribe, dispense or sell medication, does not process patient payments, and does not give medical advice. Always follow the instructions of your prescriber and pharmacist and read the medication guide supplied with your medicine.