title: Rationale and conditions for the requirement of chiral bioanalytical methods in bioequivalence studies.
abstract: OBJECTIVE
  The aim of the present work was to assess the need for chiral bioanalytical methods in bioequivalence studies.
  
  
  METHODS
  The samples from a bioequivalence study of two ibuprofen 2% oral suspensions that had shown bioequivalence for AUC and C(max), but not for t(max) (medians of 2.0 and 0.75 h) with a non-chiral method were assayed with a chiral method to investigate whether there was an actual difference in the rate of absorption within the limits of C(max) and AUC bioequivalence.
  
  
  RESULTS
  The non-chiral method and the sum of concentrations of both enantiomers obtained with the chiral method gave a similar outcome (90% CI C(max) non-chiral: 82.77-96.09, sum of enantiomers: 82.19-98.23; 90% CI AUC(t) non-chiral: 107.23-115.49, sum of enantiomers: 105.73-121.35). However, the chiral method showed differences in AUC and C(max) that resulted in non-bioequivalence for the individual enantiomers (90% CI C(max) S-ibuprofen: 76.05-91.36, R-ibuprofen: 87.84-113.05; 90% CI AUC(t) S-ibuprofen: 96.67-105.86, R-ibuprofen: 118.86-142.24). The differences in the pharmacokinetics of each enantiomer, and thus in the enantiomer concentration ratio, were dependent on the rate of absorption.
  
  
  CONCLUSIONS
  Due to the fact that in bioequivalence studies the rate of absorption of the new product is unknown, chiral bioanalytical methods should be employed for chiral drugs, such as ibuprofen, whose enantiomers exhibit different pharmacodynamic characteristics and whose enantiomer concentration ratio might be modified by the rate of absorption, irrespective of whether the eutomer is the minor enantiomer or the similarity of the pharmacokinetics of the enantiomers at a given rate of absorption.
authors.affiliation: Departamento Farmacia y Tecnología Farmacéutica, Facultad de Farmacia, Universidad Complutense de Madrid, Plaza Ramón y Cajal, 28040, Madrid, Spain.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Torrado
authors.forename: María
authors.initials: M
authors.lastname: Blanco
authors.forename: Magí
authors.initials: M
authors.lastname: Farré
authors.forename: Pere
authors.initials: P
authors.lastname: Roset
authors.forename: Alfredo
authors.initials: A
authors.lastname: García-Arieta
mesh_terms: D000284:Administration, Oral; D000704:Analysis of Variance; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001681:Biological Assay / Q000379:methods*; D018592:Cross-Over Studies; D006801:Humans; D007052:Ibuprofen / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D007408:Intestinal Absorption; D008956:Models, Chemical; D013237:Stereoisomerism; D013810:Therapeutic Equivalency
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D007052:Ibuprofen