WEDNESDAY, Jan. 25, 2017 (HealthDay News) -- A newly approved drug may help in the battle against Clostridium difficile -- a potentially fatal "superbug" gut infection that has become a scourge in U.S. hospitals.

In two clinical trials, researchers found that the drug, called bezlotoxumab (Zinplava), cut the risk of a recurrent C. difficile infection by almost 40 percent.

That's important, because the gut infection commonly comes back after treatment with antibiotics -- around 20 percent of the time, according to the U.S. Centers for Disease Control and Prevention.

The infection can also make people seriously ill, with symptoms ranging from diarrhea to life-threatening inflammation of the colon, the CDC says.

Zinplava has already been approved by the U.S. Food and Drug Administration, and it should be available early this year, according to Merck, the drug's maker.

That approval was based on the findings of two Merck-funded trials, published in the Jan. 26 issue of the New England Journal of Medicine.

The drug "will give us another tool in the toolbox" for fighting C. difficile infections, said Dr. Johan Bakken, former president of the Infectious Diseases Society of America.

And additional weapons are welcome, he said, given the scope the problem.

C. difficile sickened almost half a million Americans in 2011, according to the most recent numbers from the CDC. An estimated 29,000 of those patients died within a month.

Most infections happen in the hospital, the CDC says.

In fact, C. difficile has become the most common hospital-acquired infection nationwide, Bakken pointed out.

The bacteria can contaminate hospital surfaces and equipment, and be transmitted to patients.

That's a particular threat when patients are on powerful antibiotics to treat an infection: The drugs kill not only harmful bacteria, but also the "good" bacteria that normally dwell in the gut and crowd out the bad ones.

"The antibiotics hit the innocent bystanders, and that allows C. difficile to get a stronghold," said Bakken, who wasn't involved in the Zinplava trials.

To treat C. difficile, doctors use more antibiotics, which actually do a good job of killing the bug. The problem, Bakken explained, is that C. difficile produces spores that can survive the onslaught.

Once the antibiotics are stopped, those spores can spring to life again and churn out illness-causing toxins.

Zinplava is not an antibiotic. It's a lab-generated "monoclonal" antibody designed to neutralize one of the C. difficile toxins -- toxin B -- and can keep it from damaging the colon lining, Bakken explained.

"But it's not meant to be used alone," he stressed. Patients receive standard antibiotics, plus an IV infusion of Zinplava.

The two trials involved over 2,600 adults who all received antibiotics for a first-time or recurrent C. difficile infection. Some were randomly assigned to receive a Zinplava infusion, while the rest received a saline infusion that served as a placebo.

Over 12 weeks, 16 percent to 17 percent of Zinplava patients suffered a recurrent infection. That compared with 26 percent to 28 percent of placebo patients, the findings showed.

The drug's main side effects included fever, nausea and diarrhea -- which affected between 5 percent and 7 percent of patients. According to Merck, there is also a concern about worsening heart failure in people who already have the disease.

The drug is not for everyone with C. difficile infection, Bakken said.

It's officially approved for people at "high risk" of a recurrence.

Plus, Bakken noted, the drug is sure to be expensive -- as monoclonal antibody drugs always are.

Dr. Mark Wilcox, the lead researcher on the trials, agreed that doctors will have to give the drug based on patients' personal odds of a recurrence.

According to Wilcox, some high-risk patients include those who are age 65 or older, have a compromised immune system or have a severe C. difficile infection.

"Bezlotoxumab was more effective in such patients," said Wilcox, a professor of medical microbiology at the University of Leeds in England. "So doctors should consider adding it to standard-of-care antibiotics according to these risk factors."

The drug is not the final answer, however.

"The recurrence rates were in the teens rather than the 20s," Bakken pointed out.

He said researchers are working on other ways to protect vulnerable patients from C. difficile -- including vaccines. They also want to figure out which "key organisms" are needed in the gut to ward off the infection, Bakken said.

A study last year hinted that "good" strains of the C. difficile bug, itself, could be beneficial. In that study, patients given antibiotics and a liquid containing non-toxic C. difficile had a lower risk of a repeat infection, versus those who drank a placebo brew.

More information

The CDC has more on C. difficile infection.