Secondary Treatment Failure — SCE Dermatology MCQ

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HardDermatopharmacologySecondary Treatment FailureSCE Dermatology

A 50-year-old man with psoriasis on a biologic develops secondary failure after 2 years of initial good response. His drug levels are adequate and anti-drug antibodies are negative. What type of treatment failure is this?

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Correct answer: B — Pharmacodynamic failure — the disease has evolved to be driven by a different pathway despite adequate drug exposure; switching to a different mechanistic class is recommended

Secondary pharmacodynamic failure (loss of response despite adequate drug levels and no anti-drug antibodies) suggests the disease has evolved — potentially with upregulation of alternative inflammatory pathways bypassing the blocked target. This contrasts with primary failure (never responded — pharmacodynamic from the outset) and secondary immunogenic failure (loss of response from anti-drug antibodies reducing drug levels). Management: switch to a biologic of a DIFFERENT mechanistic class to target the presumed alternative pathway. Evidence suggests that class-switching (e.g., anti-TNF → IL-17 or IL-23) produces better outcomes than within-class switching for secondary pharmacodynamic failure.

Reference: BAD 2020 Biologic Guidelines; BJD TDM