Optimer's North American phase 3 Fidaxomicin study results presented at the 49th ICAAC

Optimer Pharmaceuticals, Inc. (Nasdaq: OPTR) today announced that new data highlighting fidaxomicin's (OPT-80) lower CDI recurrence rates and reduced risk of vancomycin-resistant enterococci (VRE) acquisition from Optimer's North American phase 3 study were presented at the 49th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in San Francisco.

"The additional data highlight fidaxomicin's unique profile as a new antibiotic class with beneficial characteristics for treating CDI," said Michael N. Chang, Ph.D., President and CEO of Optimer Pharmaceuticals. "These analyses describe fidaxomicin's low recurrence rate, safety profile, potent activity against CDI, and minimal disruption to the normal intestinal flora. We think fidaxomicin has the potential to be the treatment of choice for CDI which is a serious unmet medical need with limited treatment options."

Yoav Golan, M.D., an investigator from the Tufts Medical Center in Boston, MA, presented additional analyses around the previously reported recurrence data showing that patients treated with fidaxomicin had a substantially lower recurrence rate (13.3%) than those treated with vancomycin (24.0%). However, the recurrence rate difference between fidaxomicin and vancomycin was even greater, 10.9% versus 24.3%, respectively, in patients who did not receive CDI therapy (either vancomycin or metronidazole) in the 24-hour pre-trial enrollment period. Dr. Golan further noted that CDI recurrence occurred significantly later in patients treated with fidaxomicin with only 3% and 9% recurrence rates respectively, versus 14% and 20% recurrence rates for vancomycin, respectively, at 10 and 20 days post-treatment.

In an oral presentation, Curtis J. Donskey, M.D., an investigator from the Cleveland VA Medical Center in Ohio, concluded that fidaxomicin is less likely than vancomycin to promote acquisition of VRE colonization in patients treated for CDI, likely due to inhibitory activity of fidaxomicin against many VRE strains and fidaxomicin's relative sparing of the intestinal flora including Bacteroides spp. The results showed that only 7% of patients treated with fidaxomicin acquired VRE versus 31% of vancomycin treated patients (p<0.001) from among a subset of 302 CDI patients, 248 of whom had a negative VRE stool sample upon entering the Phase 3 trial. In addition, 63% of the patients treated with fidaxomicin were found to retain greater than 100,000 Bacteroides bacteria per gram of stool versus only 13% of the vancomycin treated patients>Bacteroides bacteria, which is a major component of the intestinal flora and prevents C. difficile overgrowth. The Bacteroides sparing effect of fidaxomicin could be one of the reasons for the lower recurrence rate observed in the Phase 3 trial.

Detailed strain typing results from the phase 3 trial presented by Dale N. Gerding, M.D., from the Hines VA Hospital in Chicago, IL, identified the various strain type groups in the study. These data show that the overall cure rate among patients harboring BI isolates is significantly lower than those with non-BI strains (85.4% vs. 95.5%>

Pam Sears, Ph.D., from Optimer Pharmaceuticals, presented results from the phase 3 study showing that there is minimal systemic absorption of fidaxomicin with all post-dose plasma measurements in the nanogram range. At the same time, the average fecal drug levels were greater than 5,000 times fidaxomicin's MIC(90)( )against C difficile. These results indicate that fidaxomicin has a favorable pharmacokinetic profile for the treatment of CDI.

Optimer's Chief Medical Officer, Sherwood L. Gorbach, M.D., presented safety results from the first phase 3 study, which show that fidaxomicin has a safety profile comparable to that of vancomycin for the treatment of CDI. Subjects from the two treatment arms had similar adverse events and serious adverse events, as well as cardiologic and clinical laboratory profiles while on study. All-cause mortality was 5.3% for fidaxomicin versus 6.5% for vancomycin.

Ellie J. Goldstein, M.D., from the R.M. Alden Research Laboratory in Santa Monica, CA, presented the antimicrobial susceptibilities of fidaxomicin, vancomycin, metronidazole, and rifaximin to C. difficile cultured from fecal specimens collected from patients at study entry and at failure/recurrence. The data showed that the susceptibility (MIC(90)) of baseline isolates did not predict clinical cure, failure, or recurrence for either fidaxomicin or vancomycin. No resistance to either fidaxomicin or vancomycin developed during the phase 3 study. Furthermore, two of the C. difficile strain typing groups, the BI and K group strains had lower susceptibilities than other groups to rifaximin and metronidazole with resistance to rifaximin occurring in 14% of the BI group and 18% of the K group.