From the Journals

Therapeutic drug monitoring pays off for arthritis patients



Therapeutic drug monitoring allowed patients with rheumatoid arthritis, psoriatic arthritis, and spondyloarthritis to reduce their dosage of tumor necrosis factor–alpha (TNF) inhibitors, based on data from 239 individuals.

Use of TNF-alpha inhibitors improves treatment response for many arthritis patients but dosage is rarely adjusted on an individual level, which may lead to unnecessary overdosing in some patients, Mogens Pfeiffer-Jensen, MD, of Aarhus (Denmark) University Hospital, and colleagues wrote.

Data from previous studies suggest that therapeutic drug monitoring (TDM) based on serum trough levels may allow for dose optimization and dose reduction in inflammatory bowel disease patients, but data in patients with arthritis are lacking, they wrote.

In a study published in the Scandinavian Journal of Rheumatology, the researchers recruited 99 patients with RA, 48 with psoriatic arthritis (PsA), and 92 with spondyloarthritis (SpA). The participants were randomized to standard care or standard care plus TDM. Serum trough levels were assessed at baseline and at every 4 months, and prescription changes or drug switches were implemented based on these levels. At baseline, 81 patients were being treated with infliximab (Remicade and biosimilars), 79 with etanercept (Enbrel), and 79 with adalimumab (Humira).

The primary endpoint was reduced drug prescription after 48 weeks.

Overall, TDM significantly reduced prescription of infliximab by 12% (P = .001) and prescription of etanercept by 15% (P = .01), compared with standard care. TDM also prolonged the interdosing intervals of etanercept by 235% (P = .02) and of adalimumab by 28% (P = .04), compared with standard care.

TDM patients taking infliximab had more frequent dose reduction and less frequent dose increases during and after the study when compared with patients who stayed with standard care; similar trends were seen with adalimumab. TDM also accelerated the switch to other biologics for patients on all three medications.

No significant differences occurred in adverse events or hospitalizations between the TDM and standard care patients.

Clinical composite scores (Disease Activity Score based on 28 joints with C-reactive protein) were reduced in patients with RA and PsA who were taking adalimumab and randomized to TDM, but no other clinical outcome differences were noted. Scores on the Health Assessment Questionnaire and global Visual Analog Scale for pain were significantly lower in patients in the TDM group who were taking infliximab and adalimumab, “indicating equally or superior sustained remission across diagnoses,” the researchers emphasized.

The findings were limited by several factors, including the variations in pathophysiology and open-label design. “However, since the TDM was based on an objective serum value and decision procedures were clear, we do not consider the potential of unconscious bias to outweigh the benefits of dose-changing abilities,” they wrote.

The researchers expressed surprise that the reduced use of TNF-alpha inhibitors did not significantly reduce adverse events or serious adverse events, compared with standard care, but they proposed that standard of care may have taken adverse events into account, because all patients had received prescriptions at least 3 months before the study.

As for clinical implications, the current costs of the biochemical assays necessary for TDM may be a barrier to implementing TDM as a standard part of daily clinical practice, the researchers added. However, the study was strengthened by the inclusion of patients with RA, PsA, and SpA, and is the first known to include patients receiving etanercept or adalimumab in an examination of TDM.

“Our data support TDM based solely on serum trough levels in [TNF-alpha inhibitors] with different pharmacokinetics as a future key player in personalized medicine for chronic rheumatoid diseases treated with biologics,” they concluded.

The study was supported by Spydspidspuljen, Region Midt, Denmark, and Department of Rheumatology, Aarhus University Hospital. The researchers had no financial conflicts to disclose.

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