Switching back and forth between a ustekinumab biosimilar and the originator changed nothing measurable

Design

Randomised, double-blinded interchangeability trial with three alternating exposures

Population

453 adults with moderate-to-severe plaque psoriasis and at least PASI 50 after a reference-product run-in

Primary outcome

AUC over the dosing interval and Cmax between weeks 52 and 64

Effect

AUCtau geometric mean ratio 0.93 (90% CI 0.89-0.98); Cmax 0.95 (90% CI 0.90-1.00); both within the 0.8-1.25 margin

The objection to biosimilar substitution has never really been about the first switch. It is about what happens when a patient is moved back and forth as pharmacy contracts change — whether repeated switching shifts drug exposure or provokes antidrug antibodies.

This randomised, double-blind study tested it directly. Patients with moderate-to-severe plaque psoriasis had a run-in of reference ustekinumab (45 mg or 90 mg by weight) at weeks 0, 4 and 16. At week 28, the 453 who had reached at least PASI 50 were randomised: 225 continued reference product at weeks 28, 40 and 52; 228 were switched to ABP 654 at week 28, back to reference at week 40, and to ABP 654 again at week 52. Primary endpoints were AUC over the dosing interval and Cmax between weeks 52 and 64.

The geometric mean ratios were 0.93 (90% CI 0.89-0.98) for AUCtau and 0.95 (90% CI 0.90-1.00) for Cmax — both confidence intervals inside the prespecified 0.8-1.25 equivalence margin. Efficacy at week 64, antidrug antibody incidence and adverse events were similar between groups.

The practical effect is that the pharmacokinetic argument against repeated switching no longer has evidence behind it for this pair. Where cost drives substitution, as it commonly does in India, that removes a reason to resist it.

• Three alternating exposures produced no measurable pharmacokinetic drift
• Antidrug antibody rates were similar — this was the mechanistic worry, and it did not appear
• Applies to this biosimilar and this reference product, not to biosimilars as a class
• Patients enrolled were responders at week 28; this says nothing about switching a non-responder
• Have the conversation before the substitution happens, not after the patient notices a different pen

Why it matters

The objection to switching a stable patient rested on a pharmacokinetic concern this trial was designed to test.

Don't overread it

Interchangeability was shown for one biosimilar and one reference product; it does not generalise to other biosimilar pairs.

The statistics, in plain English

An equivalence study asks a different question from a superiority trial: it asks whether the difference is small enough not to matter, against a margin set in advance. Here the margin was 0.8 to 1.25 for the ratio of drug exposure, and both confidence intervals fell inside it. The Cmax interval reaching exactly 1.00 at its upper bound is not a warning sign — it is well within the margin.

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