Pharmacokinetics of a commercially available product and a compounded formulation of extended-release levetiracetam after oral administration of a single dose in cats.

OBJECTIVE: To compare pharmacokinetics of levetiracetam in serum and CSF of cats after oral administration of extended-release (ER) levetiracetam. ANIMALS: 9 healthy cats. PROCEDURES: Cats received 1 dose of a commercially available ER levetiracetam product (500 mg, PO). Thirteen blood and 10 CSF samples were collected over a 24-hour period for pharmacokinetic analysis. After 1 week, cats received 1 dose of a compounded ER levetiracetam formulation (500 mg, PO), and samples were obtained at the same times for analysis. RESULTS: CSF concentrations of levetiracetam closely paralleled serum concentrations. There were significant differences between the commercially available product and the compounded formulation for mean ± SD serum maximum concentration (Cmax; 126 ± 33 µg/mL and 169 ± 51 µg/mL, respectively), Cmax corrected for dose (0.83 ± 0.10 µg/mL/mg and 1.10 ± 0.28 µg/mL/mg, respectively), and time to Cmax (5.1 ± 1.6 hours and 3.1 ± 1.5 hours, respectively). Half-life for the commercially available product and compounded formulation of ER levetiracetam was 4.3 ± 2.0 hours and 5.0 ± 1.6 hours, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The commercially available product and compounded formulation of ER levetiracetam both maintained concentrations in healthy cats 12 hours after oral administration that have been found to be therapeutic in humans (ie, 5 µg/mL). Results of this study supported dosing intervals of 12 hours, and potentially 24 hours, for oral administration of ER levetiracetam to cats. Monitoring of serum concentrations of levetiracetam can be used as an accurate representation of levetiracetam concentrations in CSF of cats.