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Rib-X Antibiotic Passes Clinical Trial, Hopes to Snag Partner

Xconomy Boston — 

Rib-X Pharmaceuticals, the New Haven, CT-based developer of novel antibiotics, is announcing today that one of its experimental treatments passed a mid-stage clinical trial for patients with a common form of pneumonia. It’s looking to deal with a Big Pharma company with the money and resources to take the drug through the next steps needed for FDA approval.

The study looked at 160 patients with mild to moderate community-acquired pneumonia, who were randomly assigned to get one of three different doses of Rib-X’s oral pill version of radezolid (pronounced ruh-DAY-zo-lid). Researchers found that 78 to 92 percent of patients were considered clinically cured, while the most common side effect was a mild irritation in the intestines.

The Rib-X antibiotic was designed with the help of a proprietary computer system that identified points of vulnerability in bacteria, and ways in which they develop resistance to existing drugs, as Ryan reported in October. The company’s goal is to create two versions of radezolid, an oral and intravenous form, so that physicians can use them to treat a wide-range of bacterial invaders, both among hospitalized patients and those who can take an oral pill at home. If Rib-X can navigate the final stage of clinical trials to prove both of these versions are effective, it will be in position to compete with one of Pfizer’s fast-growing products, linezolid (Zyvox), which generated $1.1 billion in sales last year.

“We feel this is very promising data,” says Susan Froshauer, Rib-X’s CEO. “We’re not seeing the kind of bone marrow suppression that you see with other treatments in the class.”

Still, the data is from a mid-stage study, so it’s too early to conclude that this drug will be a winner. The point was to assess the lowest possible dose at which Rib-X could see an anti-bacterial effect, Froshauer says. Researchers saw comparable effectiveness at all three doses tested, with 300 milligrams taken once a day as the lowest option. The study, as is customary at this early stage of the game, didn’t directly compare the Rib-X drug to the standard of treatment with the Pfizer product.

The next step will be for Rib-X to develop an intravenous formulation and run a similar dose-ranging trial, Froshauer says. The company plans to explore how well the drug performs in further trials against other bugs, like complex skin infections and tough forms of pneumonia, Froshauer says. This will take time and money. Even though Rib-X has raised at least $148 million in its eight-year history from some deep-pocketed investors, the time is right to talk with Big Pharma companies that bring more money and expertise to the program as it gears up for the final stages of development. This applies not just to radezolid, but delafloxacin, another antibiotic the company is developing that’s ready for Phase III clinical trials, Froshauer says.

“We are active in partnering discussions, and it’s a key part of our strategy,” Froshauer says. “To advance them on a timeline that they’re ready for will require additional cash from partners.”

One of the key messages Froshauer will surely have to deliver to partners is how the Rib-X drug is really different from others in its class, known as oxazolidinones. This class includes Pfizer’s linezolid (Zyvox), and an experimental treatment from San Diego-based Trius Therapeutics that has shown some promise in a trial of more than 180 patients. Rib-X says its drug has an advantage in that it doesn’t appear to suppress the bone marrow in ways that forces some patients to quit taking their medication.

It’s hard to say yet how a big a deal that will ultimately be for Rib-X, because it is still sifting through the data in detail to see what’s most clinically meaningful from the trial. The company is gearing up for the big annual meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy from Sept. 12-15 in San Francisco. It may or may not present the latest data on radezolid at that meeting, but it’s sure to come up in partnership talks, Froshauer says. “This is all very new,” she says.