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Perianal Crohn Infliximab TDM — RACP Adult Medicine MCQ

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ModerateGastroenterologyPerianal Crohn Infliximab TDMRACP Adult Medicine

A 40-year-old man with Crohn disease on infliximab develops a perianal abscess requiring surgical drainage. Intra-operative findings show a complex fistula-in-ano with multiple tracts. He has a seton placed. Post-operatively, his CRP rises and infliximab trough levels are subtherapeutic (2 μg/mL, target >5). Anti-infliximab antibodies are negative. What is the most appropriate management?

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Correct answer: B — Dose-escalate infliximab (increase dose or shorten interval)

Subtherapeutic infliximab levels without anti-drug antibodies = pharmacokinetic failure (increased drug clearance — common in active perianal disease with high inflammatory burden). Dose escalation (increase to 10 mg/kg or shorten interval to q6 weeks) is the appropriate response. TDM-guided dosing (target trough >5 μg/mL for perianal disease, some advocate >10 μg/mL) improves outcomes. If anti-drug antibodies were positive, switching to a different anti-TNF or out-of-class would be preferred.

Reference: GESA – 2024 – Crohn Perianal; ECCO 2024; PANTS Study