The precise mechanism of Levetiracetam is unknown. 1 Levetiracetam is not extensively metabolized in humans, with 66% of an administered dose excreted unchanged in urine. About 24% of an administered dose is metabolized to an inactive metabolite by enzymatic hydrolysis of the acetamide group; with dose not depend on hepatic cytochrome P-450 (CYP) isoenzymes. Levetiracetam is not a high-affinity substrate for or inhibitor of CYP isoenzymes.