UC Irvine

Background: Therapeutic Drug Monitoring is part of standard patient care and utilizes pharmacokinetic tests to measure trough drug levels in patients to guide patient therapy. Studies have suggested improved patient outcomes can be achieved by maintaining a target therapeutic trough concentration of drug through individualized patient dosage. However, the association between drug concentration in serum and patient outcomes is still poorly understood.

Objectives: Evaluate the association between serum drug levels, disease activity, and patient characteristics. Identify if an optimal therapeutic drug level in serum is associated with lower disease activity. Evaluate whether elevated drug levels in serum increase immune response against drug.

Design, setting, and participants: The study is a retrospective cohort study. Eligible study participants were identified through the arthritis internet registry from 2011 through 2016. The study included a total of 57 patients, 47 female and 10 males, 30 to 81 years of age, clinically diagnosed with rheumatoid arthritis and being treated with infliximab drug.

Methods: The study is a retrospective cohort study. Patient characteristics and disease outcomes were compared using independent sample t-tests for continuous variables and x2 tests for categorical variables. Regression analysis was conducted to establish the correlation between disease activity and drug level in serum.

Results: Therapeutic drug monitoring (TDM) guidelines for Infliximab trough levels for maintenance therapy did not show association with patient outcomes. Current Therapeutic drug monitoring (TDM) guidelines individualizing patient therapy show no difference in clinical or biological remission between patients maintaining recommended trough guidelines and those who do not. A significant association was observed between drug trough levels above 5 mcg/mL and anti-drug antibody levels. The results suggest that patients maintaining drug levels above 5 mcg/mL are less likely to develop anti-drug antibodies (p=0.020).

Discussion: TDM may benefit in individualizing patient dosage to maintain target drug levels to reduce immune response against anti-drug antibodies. However, a significant association between disease activity and trough drug levels was not observed