To better serve our veterinary clients treating animals with anticonvulsant therapy, the MSU VDL has recently added tests for therapeutic monitoring of Levetiracetam (Keppra) and Zonisamide. These drugs are human medications that have been adopted for veterinary use in situations where the animal becomes refractory to both phenobarbital and potassium bromide. As with phenobarbital or potassium bromide therapy, therapeutic monitoring is important. Therapeutic and toxic effects of drug therapy are related to serum concentrations.
Levetiracetam (Keppra, test code 70057)
Keppra is a new generation antiepileptic drug that is advantageous in that it is nearly 100% bioavailable, has a large margin of safety and, unlike phenobarbital, it is not metabolized by the hepatic cytochrome P450 system. Although a therapeutic range has not been established for either dogs or cats, the therapeutic range for humans (5 – 45 µg/mL) can be adopted and the animal should be monitored to establish baseline and then be repeated if the patient becomes uncontrolled or the owner is noncompliant.
Zonisamide (test code 70056)
Zonisamide is another human anticonvulsant drug adopted for veterinary use with a high margin of safety. Unlike levetiracetam, zonisamide is metabolized by hepatic cytochrome P450 and serum concentrations may be influenced by phenobarbital and related drugs. Similar to levetiracetam, a species-specific therapeutic range is not available for dogs and cats. Therefore, adoption of the therapeutic range for humans (10-40 µg/mL) is acceptable and drug monitoring is important.
It is important to remember that therapeutic drug monitoring parameters are simply guidelines and are not intended to replace clinical assessment and professional judgment. For both tests, a minimum of 0.5 mL of serum collected just prior to the next dose (trough) is appropriate. Analysis is performed by liquid chromatography.
Dewey, C. W. (2006). Anticonvulsant therapy in dogs and cats. Veterinary Clinics: Small Animal Practice, 36(5), 1107-1127.