Cost-effectiveness of routine measuring of serum drug concentrations and anti-drug antibodies in treatment of rheumatoid arthritis patients with TNF-α blockers.

Monitoring of anti-drug antibodies (ADAbs) or serum concentrations of biologicals in treatment of rheumatoid arthritis could provide an explanation for a loss of efficacy and help in the choice of subsequent medication. Current clinical practices do not generally include such monitoring of tumor necrosis factor (TNF)-α blockers on a routine basis. The main aims of this study were to estimate the probabilities of optimal and nonoptimal treatment decisions if infliximab or adalimumab drug trough level (DL) and ADAbs are tested or not in rheumatoid arthritis, and to model cost-effectiveness of performing such monitoring on a routine basis. Data on DLs and ADAbs concentrations were obtained in Finland from clinically requested monitoring analyses of 486 and 1,137 samples from patients on adalimumab and infliximab, respectively. DL was within the target range in 42% of samples from adalimumab- and 50.4% of infliximab-treated patients. ADAbs were detected in approximately 20% and 13.5% of samples from adalimumab- and infliximab-treated patients, respectively. ADAbs were found in 52.3% and 41.3% of those with low adalimumab or infliximab DLs, respectively. The monitoring data were incorporated into probabilities for making the optimal treatment decision. Economic impact of clinical decision-making was modeled in a short-term (3-6 months) scenario with 100 hypothetical patients. In the model, the combined measurement of DLs and ADAbs was cost-saving compared to the nontesting scenario when the monitoring results affected the treatment decision in at least 2-5 of 100 patients, a proportion which is easily exceeded in real-life clinical practice. This study indicates that routine monitoring of drug level and ADAbs is cost-beneficial in clinical practice, thereby improving the decision-making process in using TNF-α blockers.