Serum levetiracetam concentrations after transdermal levetiracetam administration, 3 times daily, to healthy cats

Background: Repeated oral administration of antiepileptic drugs can be challenging for cat owners, resulting in reduced compliance, poor seizure control, and reduced quality of life for cats. Levetiracetam (LEV) has several properties that make it an appealing drug for transdermal application. Objectives: The aims were to (1) determine if transdermal LEV, in a lipophilic, liposomic cream vehicle, resulted in serum concentrations above 5 μg/mL; (2) identify clinical adverse effects; and (3) evaluate the concentration of LEV in a lipophilic liposomic cream at set intervals. Animals: Six healthy, client-owned cats weighing ≤5 kg. Methods: Prospective clinical trial. Transdermal LEV was applied to the inner pinna at a dosage of 60 mg/kg (400 mg/mL concentration) at home for 6 days. Day 7, cats were hospitalized for blood sample collection for LEV concentration at times 0 (before dose administration), 0.5, 1, 2, 3, and 4 hours after administration. Results: Median (range) timed serum concentrations were 16.6 (8.6-39.6) μg/mL, 16.1 (6.8-34.4) μg/mL, 15.4 (10.1-36.7) μg/mL, 17.4 (9.2-32.7) μg/mL, 15.1 (8.3-25.9) μg/mL, and 14.8 (11.9-28.4) μg/mL, respectively. Adverse events were limited to sedation (1/6 cats) and pinna crusting (1/6 cats). The LEV, in the proposed vehicle, retained concentration above 95% at 400 mg/mL up to 5 weeks. Conclusions and Clinical Importance: Thrice daily transdermal LEV resulted in median serum concentrations ≥5 μg/mL throughout the sampling period and clinical adverse events were minimal. Transdermal LEV can provide an alternative for cats resistant to administration of other forms of anticonvulsant medication.