Earnings call transcript excerpts c/o SeekingAlpha.
Turning to ENTEREG, we're starting to see the positive results of our learning last year. The first quarter this year looks particularly strong, up close to 19% in net revenue against Q1 last year. Remember that in Q1 of last year, we were just starting the relaunch of ENTEREG and had not begun to rollout the effort to all hospitals. For the full year for ENTEREG, we are on target against the 2013 net revenue guidance we provided, a range of between $45 million and $50 million.
Finally, we continue to generate service revenues for our support of DIFICID in U.S. hospitals, as co-promote partner for Optima. This relationship is set to end in late July, when our 2-year agreement expires.
I'll briefly touch on surotomycin, our Phase III program in development as a potential treatment for C. diff. Enrollment is progressing in line with our plan to submit an NDA and MAA in the second half of 2015. Based on what we've seen through Phase II, along with the inherent qualities of the cyclic lipopeptide, we believe surotomycin has the potential to become a valued treatment option for patients with this very serious disease.
Turning to our third Phase III program, Bevenopran, in development as a potential therapy for treating opioid-induced constipation. We are very pleased with enrollment to date and the long-term safety trial and we continue to expect that we will begin enrollment in the efficacy trials by the end of 2Q
And then surotomycin for C. diff, are those 2 Phase III studies designed to enough number of patients with NAP-1 strain. So if the surotomycin show -- has superior efficacy over vancomycin, should we be able to see the difference from the data?
Well, first and foremost, our design is to be able to show noninferiority to vancomycin on response, but superiority to vancomycin with respect to relapse or recurrence. So very similar to the design of the design of the Optimer trials. With respect to NAP-1, we do expect to have roughly 1/3 of the strains, generally, that's what we had in our Phase II study, although the geographic spread is a little different. So we will have significant numbers of NAP-1 strains to be able to see whether there's effect on NAP-1 strains either both in response and in relapse or recurrence. But it's not powered to show that difference, that's the important part. The powering is around recurrence rates, not around NAP-1 responsiveness.
And then, also wondering what your latest thoughts on the commercial opportunities in C. diff? Based on how DIFICID's done over the last 1.5 year or so, what are your thoughts on prospects for surotomycin? Have those changed?
Regarding C. diff, we obviously have had a chance to get to know this market over the last couple of years. We've been very pleased with our partnership and relationship with Optimer, though it is coming to an end in July. We remain very enthusiastic about this market. We know some of the challenges that exist in the market that Optimer has had to deal with that we'll have to deal with. But we do think that our product has the potential to be differentiated and has the potential to drive worldwide sales in the $400 million to $500 million range. We would remain committed to those numbers and believe that those are possible. So this market is kind of broken a little bit differently maybe than some people expected. But I think the fact that we've been able to participate in it the last couple of years makes us very well prepared to launch surotomycin if in fact it is successful.