In psoriatic arthritis, TNFi drug-level testing may predict 12-month response

MADRID — In psoriatic arthritis patients initiating an adalimumab regimen, tumor necrosis factor-alpha inhibitor drug-level testing may have utility in determining 12-month treatment response and disability, according to findings presented at the EULAR Annual Congress.

Moreover, an inverse relationship to drug levels was observed for both the presence of antidrug antibodies and BMI, the study found.

In the study, researchers evaluated 75 participants (mean age, 51±12 years; 61% were female) in the OUTPASS study, a national U.K. prospective observational cohort. Of the patients assessed, 49 had initiated adalimumab treatment and 26 were on an etanercept regimen. The researchers collected blood samples at 3 months, 6 months and 12 months after they began tumor necrosis factor inhibitor therapy. Radioimmunoassay and random drug levels using ELISA assays were employed to measure antidrug antibodies (ADAb). At each visit, all patients were measured for DAS28. The researchers used generalized estimating equation (GEE) to determine the association between ADAbs and drug levels, both biomarkers and treatment response (determined by change in DAS28 score from pre-treatment to 12-months post-treatment, Health assessment questionnaire [HAQ] and the correlation between longitudinal/baseline factors and drug levels).

Of the serum samples taken, 264 were deemed appropriate for pharmacological testing (n=174 adalimumab; n=90 etanercept). The median BMI of the patients evaluated was 28.9.

Investigators found ADAbs were detected in 20% of adalimumab-treated patients, but no etanercept-treated patients were positive for ADAbs. No significant correlation was seen between etanercept drug levels and change in DAS28 during a period of 12 months.

GEE was used to identify a significant association between adalimumab levels and 12-month change in DAS28 and an inverse association between adalimumab levels and HAQ scores at 12 months. No independent correlation was seen between change in DAS28 level and ADAb level. Using concentration-effect curves, the researchers determined that an optimal treatment response at 6 months was achieved with adalimumab concentrations between 4.5 mg/L to 8.5 mg/L.

“We then looked at predictors of the low drug levels in both adalimumab- and etanercept-treating patients using GEE in a fully adjusted model,” researcher Megha Jani, MD, said in a press conference. “The antidrug antibody status was significantly associated with low adalimumab drug levels across all time points. Interestingly, so was body mass index, specifically when patients had a BMI of more than or equal to 30.” – Jennifer Byrne

Reference:

Jani M, et al. Abstract # OP0110. Presented at: EULAR Annual Congress; June 14-17, 2017; Madrid.

Disclosures: Jani reports grant/research support from AbbVie, UCB and Pfizer. Chinoy reports grant/research support from Novartis and AbbVie; is a consultant for Eli Lilly and Novartis; is on the speakers bureau for UCB and A. Barton Grant; receives research support from Eli Lilly and is on the speakers bureau for Roche Chugai and Pfizer.