QUARTERLY BEAT / APRIL 2025
ANTICONVULSANT MEDICATION
DRUG BLOOD LEVEL
THERAPEUTIC LEVEL
· 2-3 weeks after initiating treatment, along with a CBC and liver profile · 2-3 weeks after any dose change · Long term q6 months with alternating q6m with a liver profile vs a full CBC and chemistry · Sampling time: ◦ Trough sample suggested, however, comparing samples from the same or very similar sample collection times is most important ◦ Peak and trough samples necessary only for animals in which a shorter half-life is expected and therefore a shorter dosing interval may be necessary to maintain appropriate drug concentrations throughout the dosing interval · “Steady-state” never truly occurs for dogs and may not in cats, because the drug DOES NOT accumulate with each dose. As such, testing can actually be quite complicated, because there is a large degree of fluctuation of the drug concentration during the dosing interval · Sampling time: ◦ Recommend a peak and trough when levetiracetam is started so you can determine your patient’s half-life · 2 weeks after starting or discontinuing phenobarbital as phenobarbital decreases the half-life of levetiracetam · I personally do not commonly evaluate these levels due to the large degree of fluctuation, cost, and safety margin of levetiracetam
· Canine: 20-40 mcg/ml · Recommend using a high end of 35 mcg/ml in most patients, though some refractory cases may need to go as high as 40 mcg/ml · Feline: 10-20 mcg/ml
Phenobarbital
· Canine and Feline: 5-45 mcg/ml
Levetiracetam
· 2.5-3 MONTHS after starting · 2-3 months after any dose change · 2-3 months after a diet change · Long term q6-12 months · Sampling time: ◦ Any time during the dosing interval
· Canine ONLY: · 1-3 mg/ml (monotherapy) · 1.5-2 mg/ml (in use with phenobarbital)
Potassium Bromide
· 2 weeks after treatment initiation, along with a liver profile · 2 weeks after any dose change · 2 weeks after starting or discontinuing phenobarbital as phenobarbital decreases the half-life of zonisamide · Long term q6-12 months · Sampling time: ◦ Trough sample suggested, however, comparing samples from the same or very similar sample collection times is most important ◦ Peak and trough samples necessary only for animals in which a shorter half-life is expected and therefore a shorter dosing interval may be necessary to maintain appropriate drug concentrations throughout the dosing interval
· Canine: 10-40 mcg/ml · Feline: 10-40 mcg/ml
Zonisamide
Pregabalin
· Clinical testing not currently available
· Canine and Feline: 2-5 mcg/ml
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