It confirmed my understanding of the meaning of meeting the primary endpoint in this trial - that prurisol (at either dose) results in a statistically significantly higher PASI75 response rate compared to placebo. This trial is powered to be able to answer the question (i.e. is big enough to provide statistically significant differences).
The previous prurisol Phase IIa trial did not show statistically significantly differences in psoriasis score changes between prurisol and placebo, but the trial was much smaller and may not have been powered to do so. It's possible they were doing more of an exploratory dose-ranging and preliminary efficacy study. I believe the primary endpoint for the Phase IIa was to see differences in IGA >=2 points. However Phase IIa only had <30 subjects per group (even fewer per protocol), and this one has >80. So, it "failed" the Phase IIa in terms of no statistically significant differences, however it was successful in showing that it could be effective at 200 mg doses and more severe psoriasis. It all depends on what was the purpose of the trial and how the trial protocol laid it all out. Pharma sponsored clinical trial protocols are typically proprietary documents. (I have read several hundred of them in my capacity as an IRB member responsible for overseeing trials at my institution).
Doesn't really matter at this point how to characterize the IIa trial in black or white - or really any of the prior trials. It showed a hint of efficacy at higher doses and more severe disease, which lead to the current trial. Here's hoping the results continue the same as before, with at least ~20-30% PASI75 response rate (vs. ~5-10% placebo) and low percentage and severity of side effects. If so, IPIX will have a very valuable drug on its hands.
