title: Pharmacokinetics of levetiracetam and its enantiomer (R)-alpha-ethyl-2-oxo-pyrrolidine acetamide in dogs.
abstract: OBJECTIVE
  The new antiepileptic drug, levetiracetam (LEV, ucb LO59), is a chiral molecule with one asymmetric carbon atom whose anticonvulsant activity is highly enantioselective. The purpose of this study was to evaluate and compare the pharmacokinetics (PK) of LEV [(S)-alpha-ethyl-2-oxo-pyrrolidine acetamide] and its enantiomer (R)-alpha-ethyl-2-oxo-pyrrolidine acetamide (REV) after i.v. administration to dogs. This is the first time that the pharmacokinetics of both enantiomers has been evaluated.
  
  
  METHODS
  Optically pure LEV and REV were synthesized, and 20 mg/kg of individual enantiomers was administered intravenously to six dogs. Plasma and urine samples were collected until 24 h, and the concentrations of LEV and REV were determined by an enantioselective assay. The levels of 2-pyrrolidone-N-butyric acid, an acid metabolite of LEV and REV, were determined by high-performance liquid chromatography (HPLC). The data were used for PK analysis of LEV and REV.
  
  
  RESULTS
  LEV and REV had similar mean +/- SD values for clearance; 1.5 +/- 0.3 ml/min/kg and volume of distribution; 0.5 +/- 0.1 L/kg. The half-life (t1/2) and mean residence time (MRT) of REV (t1/2, 4.3 +/- 0.8 h, and MRT, 6.0 +/- 1.1 h) were, however, significantly longer than those of LEV (t1/2, 3.6 +/- 0.8 h, and MRT, 5.0 +/- 1.2 h). The renal clearance and fraction excreted unchanged for LEV and REV were significantly different.
  
  
  CONCLUSIONS
  In addition to the enantioselective pharmacodynamics, alpha-ethyl-2-oxo-pyrrolidine acetamide has enantioselective PK. The enantioselectivity was observed in renal clearance. Because REV has more favorable PK in dogs than LEV, the higher antiepileptic potency of LEV is more likely due to intrinsic pharmacodynamic activity rather than to enantioselective PK.
authors.affiliation: Department of Pharmaceutics and Medicinal Chemistry and Natural Products, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: N
authors.initials: N
authors.lastname: Isoherranen
authors.forename: B
authors.initials: B
authors.lastname: Yagen
authors.forename: S
authors.initials: S
authors.lastname: Soback
authors.forename: M
authors.initials: M
authors.lastname: Roeder
authors.forename: V
authors.initials: V
authors.lastname: Schurig
authors.forename: M
authors.initials: M
authors.lastname: Bialer
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D004285:Dogs; D006207:Half-Life; D000077287:Levetiracetam; D008297:Male; D010889:Piracetam / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics*; D013237:Stereoisomerism
chemical_list: D000927:Anticonvulsants; D000077287:Levetiracetam; D010889:Piracetam