Minimum Infliximab Dosage for Keeping Serum Infliximab Levels Greater than 1 µg/mL among Patients with Rheumatoid Arthritis.

Infliximab shows drastic efficacy for controlling inflammation in rheumatoid arthritis (RA), though the ideal dose of infliximab to keep suppressing inflammation has not yet been identified. Recently, it has been evidenced that the minimum trough serum infliximab levels required for suppressing inflammation are greater than 1 µg/mL. This cross-sectional study was designed to identify the minimum dosage of infliximab for maintaining serum infliximab levels greater than 1 µg/mL. Thirty seven RA patients were enrolled in this study and they were divided into two groups (high-infliximab vs. low-infliximab) in reference to Remi-check Q® , a kit for examining serum infliximab levels above/below 1 µg/mL by LC. Infliximab dosage (p=0.06) and dosage interval (p=0.05) had trends to have differences between groups. A formula calculated by infliximab dosage divided by dosage interval and body weight (mg/weeks/kg) was shown to have significantly higher levels among high-infliximab group (p=0.04). Based on whether serum infliximab levels above/below 1 µg/mL and values led by the equation, infliximab dosage/infliximab interval/body weight (mg/weeks/kg), a receiver operating characteristic curve (ROC) was depicted with area under the ROC curve 0.750 and the cut-off point for the serum infliximab levels greater than 1 µg/mL was identified as infliximab dosage/infliximab interval/body weight ≧0.750 with the sensitivity 0.393 and the specificity 1.000. In conclusion, we identified that the minimum infliximab dosage to maintain serum infliximab levels greater than 1 µg/mL was infliximab dose/dosage interval/body weight (mg/weeks/kg)≥0.750.