Therapeutic Drug Monitoring in Patients with Suboptimal Response to Adalimumab for Hidradenitis Suppurativa: A Retrospective Case Series.

Background: Adalimumab, a tumor necrosis factor-α inhibitor, is a biologic used for the treatment of moderate-to-severe hidradenitis suppurativa (HS). It is well known that patients may experience loss of efficacy from its use in other conditions, and it is suggested that developing a strategy for therapeutic drug monitoring (TDM) may help secure optimal clinical outcomes.

Objectives: We sought to determine serum adalimumab concentrations and anti-adalimumab antibody (AAA) status in patients with moderate-to-severe HS.

Methods: A retrospective case series of 38 patients with suboptimal response to adalimumab 40 mg weekly was conducted at a community dermatology clinic. Adalimumab serum trough levels, AAA status, and inflammatory biomarkers were collected. Blood was drawn on identification of suboptimal response (after a minimum of 12 weeks) and was collected once prior to receiving the next scheduled dose. Kruskal-Wallis and Chi-squared tests were used for data analysis.

Results: A total of 38 patients had a median adalimumab trough concentration of 8.76 (interquartile range [IQR] 1.3-12.5) µg/mL. The median duration of adalimumab therapy of all patients was 21 (IQR 12-24) months. AAAs were detected in nine patients (24%), and all had subtherapeutic serum concentrations (< 6 µg/mL). Patients who were AAA+ had a significantly lower median adalimumab concentration than those who were AAA- (0.02 µg/mL [range 0.02-0.81] vs. 10.14 [range 0.76-48.00]; p = 0.0006).

Conclusion: Patients with AAAs had significantly lower serum adalimumab levels. The current study suggests that TDM may identify underlying reasons for suboptimal response and detect patients who may benefit from dose optimization strategies.