Design: Phase 3b randomised, double-blind, placebo-controlled trial, week 48 results
Population: 1,020 biologic-naive adults with active, erosive PsA
Primary outcome: ACR responses and radiographic progression through week 48
Effect: ACR20 71-74%; mean vdH-S change 0.60-0.78 with continuous guselkumab

APEX randomised 1,020 biologic-naive adults with active, erosive psoriatic arthritis to guselkumab every four weeks, guselkumab every eight weeks, or placebo switching to guselkumab at week 24. Week 24 results showed benefit on joints and structural damage; this report covers week 48.

With continuous guselkumab, ACR20, 50 and 70 responses at week 48 were 71-74%, 51-56% and 31-35%, and mean change in modified van der Heijde-Sharp score was 0.60-0.78. PASI90 was reached by 74-80% and minimal disease activity by 36-41%. In patients switched from placebo, radiographic progression slowed from 0.96 in the first 24 weeks to 0.41 in the next 24. Adverse event rates were stable.

After week 24 there is no placebo comparison, so week 48 results describe durability rather than a controlled effect.

The data support guselkumab as an option in erosive PsA, including for structural protection.

ACR50 at week 48 was reached by about half of patients on continuous guselkumab.
Radiographic progression stayed low with both dosing intervals.
Progression slowed after placebo patients switched to guselkumab.
Three-quarters reached PASI90, relevant where skin disease is prominent.
There is no placebo control after week 24.

Why it matters

Evidence for structural protection with IL-23 inhibitors in PsA has been thinner than for TNF inhibitors.

The statistics, in plain English

Without a placebo group after week 24, week 48 figures show whether responses lasted, not how much was due to the drug. The fall in progression after switching is a within-group comparison.