Design: Randomised, double-blind interchangeability trial
Population: 453 adults with moderate-to-severe plaque psoriasis responding to reference ustekinumab
Primary outcome: AUCtau and Cmax between weeks 52 and 64
Effect: Geometric mean ratio AUCtau 0.93 (90% CI 0.89–0.98); Cmax 0.95 (0.90–1.00); efficacy and antibodies similar

In the US, an FDA interchangeability designation lets a pharmacist substitute the biosimilar for the reference product without the prescriber, subject to state law; the designation is specific to the US. The worry has always been that repeated switching might provoke antidrug antibodies or loss of response. This randomised double-blind trial tested exactly that for ABP 654, a biosimilar of ustekinumab.

After a 28-week run-in on reference ustekinumab, 453 patients with moderate-to-severe plaque psoriasis who had reached at least PASI 50 were randomised to continue the reference product or switch three times (biosimilar at week 28, reference at 40, biosimilar at 52). Between weeks 52 and 64, the ratio of drug exposure between the switching and continued groups was 0.93 (90% CI 0.89 to 0.98) for area under the curve and 0.95 (0.90 to 1.00) for peak concentration, both inside the prespecified 0.80 to 1.25 margin. PASI response, antidrug antibodies and adverse events were similar.

For practice, this addresses the main clinical objection to switching a stable patient to a biosimilar ustekinumab for cost, which matters where patients pay out of pocket. Whether ABP 654 itself is marketed in India is not established; the principle applies to biosimilars with similar switching data.

Switch a stable psoriasis patient from reference ustekinumab to a biosimilar with switching data when cost is a barrier.
Tell the patient that three switches in this trial did not change drug levels, response or antibody formation.
Keep the dose and interval unchanged at the switch (45 mg, or 90 mg above 100 kg).
Record the product name and batch at each injection so any loss of response can be traced.
Check that the specific biosimilar you use has comparable switching or interchangeability data.

Why it matters

It addresses the main clinical objection to cost-driven switching of a biologic that many patients cannot otherwise afford.

The statistics, in plain English

Bioequivalence trials use a 90% confidence interval for the ratio of drug exposure and require it to fall between 0.80 and 1.25. Here both intervals sat well inside that range, so drug exposure after switching was equivalent to continuing the reference product.