title: Verification of a decision analytic model assumption using real-world practice data: implications for the cost effectiveness of cyclo-oxygenase 2 inhibitors (COX-2s).
abstract: OBJECTIVE
  To verify the gastroprotective agent (GPA) rate assumption used in cost-effectiveness models for cyclo-oxygenase 2 inhibitors (COX-2s) and to re-estimate model outcomes using GPA rates from actual practice.
  
  
  METHODS
  Prescription and medical claims data obtained from January 1, 1999, through May 31, 2001, from a large preferred provider organization in the Midwest, were used to estimate GPA rates within 3 groups of patients aged at least 18 years who were new to nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) and COX-2 therapy: all new NSAID users, new NSAID users with a diagnosis of rheumatoid arthritis (RA) or osteoarthritis (OA), and a matched cohort of new NSAID users.
  
  
  RESULTS
  Of the more than 319,000 members with at least 1 day of eligibility, 1900 met the study inclusion criteria for new NSAID users, 289 had a diagnosis of OA or RA, and 1232 were included in the matched cohort. Gastroprotective agent estimates for nonselective NSAID and COX-2 users were consistent across all 3 samples (all new NSAID users, new NSAID users with a diagnosis of OA or RA, and the matched cohort), with COX-2 GPA rates of 22%, 21%, and 20%, and nonselective NSAID GPA rates of 15%, 15%, and 18%, respectively. Re-estimation of the cost-effectiveness model increased the cost per year of life saved for COX-2s from $18,614 to more than $100,000.
  
  
  CONCLUSIONS
  Contrary to COX-2 cost-effectiveness model assumptions, the rate of GPA use is positive and marginally higher among COX-2 users than among nonselective NSAID users. These findings call into question the use of expert opinion in estimating practice pattern model inputs prior to a product's use in clinical practice. A re-evaluation of COX-2 cost-effectiveness models is warranted.
authors.affiliation: Office of Research and Planning, Express Scripts, Inc., 13900 Riverport Drive, Maryland Heights, MO 63043, USA. ecox@express-scripts.com
authors.forename: Emily R
authors.initials: ER
authors.lastname: Cox
authors.forename: Brenda
authors.initials: B
authors.lastname: Motheral
authors.forename: Doug
authors.initials: D
authors.lastname: Mager
mesh_terms: D000328:Adult; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000009:adverse effects / Q000191:economics* / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000188:drug therapy*; D003362:Cost-Benefit Analysis; D016861:Cyclooxygenase Inhibitors / Q000009:adverse effects / Q000191:economics* / Q000627:therapeutic use*; D003661:Decision Support Techniques; D004363:Drug Utilization / Q000191:economics*; D005260:Female; D005765:Gastrointestinal Agents / Q000191:economics / Q000627:therapeutic use; D006801:Humans; D007356:Insurance, Pharmaceutical Services; D008297:Male; D008875:Middle Aged; D015146:Midwestern United States; D017059:Models, Econometric; D010003:Osteoarthritis / Q000188:drug therapy*; D011243:Preferred Provider Organizations / Q000191:economics*
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D016861:Cyclooxygenase Inhibitors; D005765:Gastrointestinal Agents