title: The importance of sample size, log-mean ratios, and intrasubject variability in the acceptance criteria of 108 bioequivalence studies.
abstract: OBJECTIVE
  Fulfilling bioequivalence criteria with highly variable drugs is difficult. The aim of this study was to compare the importance of sample size, intrasubject variability, and the point estimate of test and reference formulations with regard to meeting bioequivalence (BE) criteria [maximum observed plasma concentration (C(max)) and area under the concentration-time curve (AUC)].
  
  
  METHODS
  We compared 137 pairs of data from BE studies with a conventional number of subjects, approximately 31-32 volunteers, developed in the last 10 years.
  
  
  RESULTS
  The third part of the studies failed to demonstrate BE, in part due to an unacceptable difference between the mean ratios (T/R) (18) but also due to high variability with small differences between formulations (17). Increasing the number of subjects is hard to justify, and expanding the confidence interval (CI) was insufficient for the most highly variable drugs.
  
  
  CONCLUSIONS
  Therefore, for low-variable drugs, the difference between formulations was the cornerstone of the fulfillment of BE criteria, but for highly variable drugs, the intrasubject coefficient of variability (ICV) was decisive. Our proposal is that for highly variable drugs that fall outside BE 90% CI limits could result in BE in the absence of formulation effect and maximal differences between formulations below 20%.
authors.affiliation: Clinical Pharmacology Department, La Paz University Hospital, School of Medicine, Autonomous University of Madrid, Arzobispo Morcillo s/n, Madrid, Spain. elena.ramirez@uam.es
authors.forename: E
authors.initials: E
authors.lastname: Ramirez
authors.forename: P
authors.initials: P
authors.lastname: Guerra
authors.forename: O
authors.initials: O
authors.lastname: Laosa
authors.forename: B
authors.initials: B
authors.lastname: Duque
authors.forename: B
authors.initials: B
authors.lastname: Tabares
authors.forename: S H
authors.initials: SH
authors.lastname: Lei
authors.forename: A J
authors.initials: AJ
authors.lastname: Carcas
authors.forename: J
authors.initials: J
authors.lastname: Frias
mesh_terms: D019540:Area Under Curve; D017321:Clinical Trials, Phase I as Topic / Q000379:methods; D016001:Confidence Intervals; D006801:Humans; D004364:Pharmaceutical Preparations / Q000592:standards; D010599:Pharmacokinetics; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D013810:Therapeutic Equivalency
chemical_list: D004364:Pharmaceutical Preparations