OBJECTIVES: Evaluation of measures of medication-taking behavior is uncommon with infusible pharmacologic agents. This study evaluated persistence and adherence measures from utilization data on the infusible anti-inflammatory biologic infliximab. METHODS: Patients were identified through the electronic health records (EHR) with ICD-9 diagnoses of rheumatoid arthritis (714.xx), psoriatic arthritis (696.xx), ulcerative colitis (556.xx), or Crohn’s disease (555.xx). Incident infliximab-treated patients between January 1, 2007 and June 30, 2011, ≥18 years of age, with ≥1maintanence dose were included. Infliximab dosing data were extracted from medical chart review and the EHR. We employed Kaplan-Meier (KM) analyses to estimate median time to treatment discontinuation and Cox regression to evaluate factors associated with discontinuation. Medication possession ratio (MPR) was calculated as sum of prescribed infusion frequency intervals divided by days from first infusion to last infusion.  Compliance was defined as MPR ≥0.80. Proportion of days covered was also explored (data not shown). Sensitivity analyses were performed for various definitions of “treatment gap” and “discontinuation”. Analyses are shown for gap of ≥90 days. For all test statistics, a p-value <0.05 was considered statistically significant. RESULTS: We identified 122 patients meeting study inclusion criteria. Mean age of patients was 45 years and 61% were female.  KM estimated a median treatment duration of 23 months and adjusted Cox regression identified African Americans at significantly greater risk for treatment discontinuation than Caucasians (hazard ratio: 4.95; 95% confidence interval: 1.11, 22.05; P=0.036). A total of 100 patients had a calculable MPR, mean and median MPR were 0.937 and 0.956, respectively, with 93% of patients compliant with treatment. Sensitivity analyses showed varied results depending on definitions. CONCLUSIONS: Patients receiving infliximab were overall compliant with therapy during a median of 23 months of treatment. Underlying definitions used with MPR and KM are important, and should be clinically meaningful and transparent.