Optimer's next step, having garnered the expected FDA approval of its Clostridium difficile antibiotic Dificid (fidaxomicin), will be to consider prophylaxis as a possible road to an expanded market for the macrolide antibiotic.

The firm is assessing which patients would benefit from preventative measures and whether they offer an economically viable market, CEO Pedro Lichtinger said during a May 31 conference call.

The firm is assessing whether there is an economically viable market in prevention.

Dificid was approved May 27 for treatment of Clostridium difficile-associated diarrhea (CDAD) in adults. Dificid acts locally in the GI track and is active primarily against C. difficile. Labeling includes language on its effect on sustaining cure, but not the prevention of recurrence indication that Optimer had originally sought (Also see "Labeling For Optimer's Dificid Includes Data On Ability To Sustain Cure Post-Treatment" - Pink Sheet, 27 May, 2011.).

The company remains interested in expanded claims, though it feels confident that it can compete on the sustained cure data on its own.

Fidaxomicin "is particularly suited for prophylaxis given its spectrum of activity, its absorption characteristics and its resistance profile at this point in time," Lichtinger pointed out. Pursuing the indication, however, is dependent on "finding a population that has an adequate incidence of the disease."

One potential target group is patients with pneumonia in hospitals, primarily in intensive care units, Lichtinger said. These patients represent at least 20% of the total CDAD population, but the rate of CDAD in the overall pneumonia population is unknown.

Current estimates are between 7% and 24%, "so we're conducting a retrospective study because, obviously, from a cost-effectiveness perspective, both in terms of conducting the trials, as well as the impact on cost, it is critical to really understand what is that rate of incidence," he pointed out.

Dificid will enter the market with a price tag of $2,800 for a 10-day course of treatment. The premium pricing reflects the drug's position as the first novel therapy for C. difficile infection and its head-start over competitors.

"The economic benefit of our treatment will be significantly superior to existing treatments, including the value that it brings to the patient and their families." Lichtinger said.

Marketing partner Cubist has its own C. difficile antibiotic in development, with Phase II results expected the second half of the year. Merck published Phase II data for its MK-3415A C. difficile candidate in 2010 and is planning a Phase III study. MK-3415A is a combination of CDA-1 and CDB-1, two fully human monoclonal antibodies that were developed by the University of Massachusetts Medical School and Merck affiliate Medarex to target and neutralize the effects of C. difficile toxins A and B.

Lichtinger pointed out ViroPharma's Vancocin (vancomycin), the only previously approved drug for C. difficile infection in the U.S., can cost about $1,000 to $1,500 for a standard treatment regimen, but the Optimer exec said about half of patients receive higher doses and/or longer durations.

The company is looking to its labeling, which declares the new antibiotic to be superior to vancomycin with regard to sustained cure at 25 days post-treatment, to justify the price differential.

Positioning As First-Line Therapy

With the superiority statement, Optimer plans to position its antibiotic as first-line treatment for CDAD. Patients with a high risk of recurrence, such as the elderly and those with renal failure or a suppressed immune system, are the target, Lichtinger said. That high-risk segment comprises up to 70% of the market, he reported.

Optimer will be marketing Dificid in conjunction with Cubist. A co-promotion deal calls for both firms initially to focus on the 1,100 hospitals where 70% of C. difficile infections occur. Cubist's 180 sales reps will visit another 1,000 hospitals that are not part of the program for Optimer's 100-person sales force (Also see "Optimer's Deal With Cubist Gives Dificid Experienced Hospital Sales Force Support" - Pink Sheet, 6 April, 2011.).

The company is required to conduct two post-marketing studies in pediatric patients, as well as a study of C. difficile resistance to Dificid. Optimer has committed to a randomized clinical trial to evaluate the drug's efficacy in treating patients with multiple CDAD recurrences. The protocol for that study is to be submitted in January 2012 and a final report in June 2016.

The desire for additional data on recurrence came up at the FDA advisory committee review of the drug – where both FDA and the panelists questioned whether Optimer had proven that claim for Dificid (Also see "Communication Of Fidaxomicin's 30-Day Effect Is Question For Labeling Discussions" - Pink Sheet, 5 April, 2011.).

By Cathy Dombrowski

Optimer Looking At Prophylaxis As Next Frontier For C. Difficile Agent Dificid

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