title: Individualized, discrete event, simulations provide insight into inter- and intra-subject variability of extended-release, drug products.
abstract: OBJECTIVE
  Develop and validate particular, concrete, and abstract yet plausible in silico mechanistic explanations for large intra- and interindividual variability observed for eleven bioequivalence study participants. Do so in the face of considerable uncertainty about mechanisms.
  
  
  METHODS
  We constructed an object-oriented, discrete event model called subject (we use small caps to distinguish computational objects from their biological counterparts). It maps abstractly to a dissolution test system and study subject to whom product was administered orally. A subject comprises four interconnected grid spaces and event mechanisms that map to different physiological features and processes. Drugs move within and between spaces. We followed an established, Iterative Refinement Protocol. Individualized mechanisms were made sufficiently complicated to achieve prespecified Similarity Criteria, but no more so. Within subjects, the dissolution space is linked to both a product-subject Interaction Space and the GI tract. The GI tract and Interaction Space connect to plasma, from which drug is eliminated.
  
  
  RESULTS
  We discovered parameterizations that enabled the eleven subject simulation results to achieve the most stringent Similarity Criteria. Simulated profiles closely resembled those with normal, odd, and double peaks. We observed important subject-by-formulation interactions within subjects.
  
  
  CONCLUSIONS
  We hypothesize that there were interactions within bioequivalence study participants corresponding to the subject-by-formulation interactions within subjects. Further progress requires methods to transition currently abstract subject mechanisms iteratively and parsimoniously to be more physiologically realistic. As that objective is achieved, the approach presented is expected to become beneficial to drug development (e.g., controlled release) and to a reduction in the number of subjects needed per study plus faster regulatory review.
authors.affiliation: Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, CA, USA.
authors.forename: Sean H J
authors.initials: SH
authors.lastname: Kim
authors.forename: Andre J
authors.initials: AJ
authors.lastname: Jackson
authors.forename: Rim
authors.initials: R
authors.lastname: Hur
authors.forename: C Anthony
authors.initials: CA
authors.lastname: Hunt
mesh_terms: D000328:Adult; D001682:Biological Availability; D003198:Computer Simulation; D003692:Delayed-Action Preparations / Q000493:pharmacokinetics* / Q000494:pharmacology; D041981:Gastrointestinal Tract / Q000187:drug effects; D006801:Humans; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D012984:Software; D013810:Therapeutic Equivalency
chemical_list: D003692:Delayed-Action Preparations; D004364:Pharmaceutical Preparations