why now and not in 200913 Feb 2019 19:51
While Arpida was developing iclaprim, the FDA was re-evaluating the requirement for the non-inferiority margin to support approval of new antibiotics. The accepted non-inferiority margin when the ASSIST clinical trials initiated was -12.5%. However, in 2008 the FDA decided that compounds for the treatment of skin and skin structure infections required a non-inferiority margin of -10% instead of -12.5%.
When Arpida conducted the data analysis from the ASSIST trials the agreed upon non-inferiority margin was -12.5%, thus the company believed that the two trials each had positive outcomes.
Following submission of the NDA, the FDA “moved the goalposts” and evaluated the data for iclaprim using a non-inferiority margin of -10%, which was consistent with the revised guidelines.
The ASSIST-1 trial did not meet the -10% non-inferiority margin, and thus Arpida received a complete response letter (CRL) from the FDA. The FDA did not indicate that there were any concerns related to the way Arpida conducted the Phase 3 trials, however the agency did request that additional studies be conducted to demonstrate the effectiveness of iclaprim, which could include non-inferiority studies comparing iclaprim to an approved comparator.
Had Arpida been aware of the -10% non-inferiority margin requirement, the ASSIST trials likely would have been designed to include more patients in order to increase the statistical power.
Other Antibiotics With Similar Regulatory Pathway as Iclaprim
Iclaprim was not the only antibiotic to fall victim to the FDA altering the guidelines for non-inferiority testing in 2008. The FDA rejected oritavancin and dalbavancin each at approximately the same time as iclaprim based on clinical data that did not meet the 10% non-inferiority cutoff. However, both oritavancin and dalbavancin were studied in additional Phase 3 clinical trials (employing the same design as the REVIVE trials with vancomycin as the comparator) and each was approved for the treatment of ABSSSI in 2014. While some investors may be nervous about a compound that was previously rejected by the FDA, the fact that other antibiotics that were not approved for a similar reason as iclaprim have now gone on to be approved, should give investors confidence that Motif is
following the correct regulatory pathway for iclaprim.
above from -
http://s1.q4cdn.com/460208960/files/News/2017/Initiation_MTFB_Bautz.pdf