Prifemilast Reaches PASI 75 in 57.4% at Week 16 in Phase 3

In a randomized, placebo-controlled phase 3 trial, 57.4% of adults with moderate to severe plaque psoriasis reached PASI 75 at week 16 on once-daily prifemilast 20 mg, compared with 10.8% on placebo.

The 10-mg arm produced a PASI 75 rate of 51.8%, making the response rate about five times the placebo result at the same assessment.

The trial randomized 505 adults 1:1:1 to once-daily prifemilast 10 mg (n = 170), 20 mg (n = 169), or placebo (n = 166) for 16 weeks. Mean age was 46.3 years, and 79.2% of participants were men.

After the placebo-controlled period, all participants entered a 36-week extension and received prifemilast 10 mg or 20 mg. Investigators reported separation from placebo by week 2 and sustained responses through week 52.

Both trials ran in China, and investigators presented their phase 2 and phase 3 findings at the 2026 Fall Clinical Dermatology Conference in Las Vegas, Nevada. Lin Cai of Peking University People’s Hospital presented the poster with co-investigators from 12 Chinese hospitals and Newsoara Biopharma.

The phase 2 dose-ranging evidence

The multicenter phase 2 trial randomized 123 adults 1:1:1:1 to four arms for 12 weeks:

• Prifemilast 6 mg, once daily (n = 31)
• Prifemilast 10 mg, once daily (n = 31)
• Prifemilast 20 mg, once daily (n = 31)
• Placebo (n = 30)

Participants had a mean age of 40.2 years, and 79.7% were men.

At week 12, every prifemilast dose produced higher PASI 75 and PASI 90 response rates than placebo, and the response increased with dose. Differences from placebo for 10 mg and 20 mg were statistically significant (P < .05).

The phase 2 trial recorded 239 adverse events in 84 patients. Most were grade 1 or 2 and resolved by the study’s end, while discontinuations were few.

Does the safety profile address class concerns?

Gastrointestinal and central nervous system adverse events have long limited tolerability of the PDE4 inhibitor class. Prifemilast, also known as HPP737, is an investigational oral inhibitor selectively targeting PDE4B and developed by Newsoara Biopharma.

Its molecular structure was designed to limit CNS penetration and slow absorption, with the aim of reducing CNS-related adverse events. That is a development goal, not proof of a safety advantage.

Without event-specific gastrointestinal or CNS rates, the design cannot yet be equated with a demonstrated reduction in either problem. A previous phase 1 study had characterized prifemilast’s pharmacokinetics and tolerability in healthy participants.

What does this change for dermatology practice?

For prescribers, the immediate change is limited: prifemilast remains investigational, so these findings do not establish a new treatment standard. What the data add is a clearly defined efficacy package for an oral candidate:

• Separation from placebo by week 2
• PASI 75 rates of 51.8% and 57.4% at week 16 with 10 mg and 20 mg, respectively
• Sustained responses through week 52
• A dose-ordered PASI 75 and PASI 90 signal in phase 2

The practical question now moves beyond whether prifemilast clears placebo. Practitioners need to know whether the low-CNS-penetration approach preserves that efficacy while avoiding the gastrointestinal and central nervous system effects that have constrained the PDE4 class.

Both studies also ran in China and enrolled approximately 79% men, leaving consistency across broader patient populations untested in the conference data. Longer follow-up and more detailed safety accounting should define whether the week-52 benefit persists and whether tolerability matches the molecule’s design promise.