Levetiracetam blood level in dogs and cats
Levetiracetam is a newer medicine for seizures in dogs and cats, used on its own or added to phenobarbital or bromide. Routine level checks are not always needed, but the vet may order one when seizures continue or when the regimen is being set. The result only makes sense together with the time of the last tablet, because the level rises and falls within hours.
What it shows
The test measures how much levetiracetam is in the serum. The medicine leaves the body quickly: its half-life is about 2–4 hours in dogs (for the regular, not extended-release form) and a few hours in cats, and it is excreted mostly unchanged in the urine. Because of that it does not build up, and a level can be checked within about a week of the start or of any change in what the vet prescribed.
With such a short half-life one sample says little about the rest of the day. Labs therefore describe a pair: a peak about 2 hours after the tablet (in some protocols 2–3 hours; for cats one lab describes about 4 hours) and a trough just before the next tablet. If only one sample is possible, a trough is preferred. The pair also lets the vet estimate the animal’s own half-life and judge how deep the level falls between tablets.
Reference books note that a link between the blood level and how well seizures are controlled has not been clearly shown, so the level is one piece of information next to the seizure diary, not a verdict by itself.
Higher than reference — what it may be a sign of
- Sample taken near the peak. Blood drawn soon after a tablet gives a much higher number than a trough sample; the time of the last tablet is part of the result.
- Slower excretion. The medicine leaves through the kidneys, so caution is described in animals with kidney disease.
- Side effects. The medicine is considered well tolerated; vomiting, wobbliness, sleepiness, agitation, loss of appetite and more thirst and urination are described in dogs, and drooling in cats.
A high result is not a signal to change anything at home: the vet decides what to do with it.
Lower than reference
A low trough may mean the level drops too far between tablets. Practical reasons include a sample taken later than planned, missed tablets, and other medicines: phenobarbital may shorten the half-life of levetiracetam, so the level falls faster. The tube matters too: enzymes in plasma keep breaking the medicine down after the blood is drawn, so labs ask for serum and a plasma sample can give a falsely low value.
Look at together with
- Phenobarbital and potassium bromide — if the animal takes them too, their levels are read together.
- Creatinine and the rest of biochemistry — the medicine is excreted by the kidneys.
- The seizure diary — dates, length and clusters of seizures matter as much as the number.
Units and conversion
Levetiracetam is reported in µg/mL. In the app this row is kept in µg/mL; if the form uses another unit, the row keeps the unit printed on the form.
Reference range
The target range is on your lab’s form. No range has been established specifically for dogs or cats: labs adopt the window used in human medicine, about 5–45 µg/mL for a trough sample, and some resources give slightly different numbers. The target for a particular animal is set by the vet together with how the seizures are going.
Cats and dogs
In cats the half-life is short, so a large part of the medicine is gone by the next tablet. One lab describes for cats a sample about 4 hours after the tablet and another shortly before the next. Drooling has been reported in cats.
In dogs the regular form has a half-life of only a few hours; extended-release forms last somewhat longer. A peak about 2 hours after the tablet and a trough before the next one show how wide the daily swing is. If the dog also takes phenobarbital, the levetiracetam level can fall faster.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Charalambous M. Epilepsy in Small Animals. Merck Veterinary Manual, professional version, full review October 2025.
- Castel A. Anticonvulsants in animals (pharmacology of the nervous system). Merck Veterinary Manual, professional version, full review April 2025.
- Auburn University Clinical Pharmacology Laboratory. Levetiracetam (Keppra®) — therapeutic drug monitoring notes.
- Auburn University College of Veterinary Medicine. Therapeutic Drug Monitoring (TDM): pricing and sample collection protocols (2023).
- Michigan State University Veterinary Diagnostic Laboratory. Therapeutic Drug Monitoring for Antiepileptic Drugs in Dogs and Cats (newsletter, winter 2018).
- Texas A&M Veterinary Medical Diagnostic Laboratory. Therapeutic drug monitoring in dogs and cats.
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.