A 30-year-old man with Crohn's disease involving the terminal ileum has failed azathioprine and is now on infliximab (IFX). He loses response after 12 months. IFX trough level is 2 μg/mL (low therapeutic), and anti-IFX antibodies are detected at high titer. What is the optimal therapeutic strategy?

• A Switch to a non-TNF mechanism biologic (vedolizumab or ustekinumab) ✓
• B Increase infliximab dose to 10 mg/kg every 4 weeks
• C Switch to an alternate anti-TNF agent (adalimumab)
• D Add methotrexate to infliximab to reduce immunogenicity

Explanation

When loss of response to infliximab is due to high anti-drug antibody (ADA) formation with low drug trough levels, switching to another anti-TNF (adalimumab) will likely result in cross-reactive immune response and further failure. Current guidelines recommend switching to a non-anti-TNF biologic with a different mechanism: vedolizumab (gut-selective α4β7 integrin inhibitor) or ustekinumab (anti-IL-12/23, p40 subunit). Dose optimization of infliximab works only when trough levels are subtherapeutic without significant antibodies (pharmacokinetic failure, not immunogenic failure).

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.