Multivariable logistic regression analyses were performed to identify covariates that may influence the exposure-response relationship for infliximab in UC patients receiving selleck inhibitor 5 mg/kg or 10 mg/kg during induction and maintenance treatment. The final logistic regression model for induction treatment through

week 8 showed that higher serum infliximab concentration at week 8, higher body weight, and female sex were associated independently with clinical response at week 8. Similar analyses conducted through week 30 of maintenance treatment showed that a higher infliximab concentration at week 30 and absence of corticosteroid therapy at baseline were associated independently with a greater probability of maintaining clinical response at week 30 (Supplementary Table 2). To identify optimal infliximab concentration target thresholds associated with clinical improvement in UC patients, ROC curves were generated for efficacy end points during both induction and maintenance treatment periods. The ROC curves for the end point of clinical response in patients who received the 5-mg/kg or 10-mg/kg infliximab dose regimen are shown in

Figure 4 for induction and maintenance treatment. Although the magnitude of the area under the ROC curves (AUC) was moderate for the induction analysis (0.63; 95% confidence interval [CI], 0.59–0.68) (ie, week-8 concentration (CW8) compared with clinical response at GDC-0068 week 8), it was significantly greater than the null value of 0.5

(P < .0001). Furthermore, the most AUC under the ROC curve for the preinfusion concentration at week 6 (CPW6) (0.62; 95% CI, 0.57–0.66) was not significantly different from that using CW8 (P = .553). In contrast, the preinfusion infliximab concentration at week 2 (CPW2) was a poor predictor of clinical response at week 8 (AUC, 0.51). With respect to the maintenance ROC curve analysis, the AUC was 0.71 (95% CI, 0.66–0.76) for the week-30 preinfusion concentration (CPW30) vs clinical response at the week-30 ROC curve and 0.75 (95% CI, 0.68–0.82) for the week-54 preinfusion concentration (CPW54) vs clinical response at the week-54 ROC curve. The AUC from the ROC curve of the serum infliximab preinfusion concentration at week 14 (CPW14) (0.68; 95% CI, 0.63–0.72) was comparable with that of the CPW30 for the clinical response at week 30 (P = .087) but was not equivalent to that from the CPW54 ROC curve for the week-54 clinical response end point (P = .041). In addition, the AUC from the CPW30 ROC curve was comparable with that from the CPW54 ROC curve (P = .746). The ROC analysis identified different target thresholds depending on the time point of the PK sampling or the efficacy assessment (Table 3). For clinical response at week 8, the threshold infliximab concentration of 41 μg/mL at week 8 was associated with a sensitivity, specificity, and positive predictive value (PPV) of 63%, 62%, and 80%, respectively.