A new injectable drug may help some very sick gout patients who don't get better with usual treatment, according to a new study.

The research was designed and funded by the pharmaceutical company Savient, which markets the drug, called Krystexxa, or pegloticase.

Patients taking the drug had fewer gout symptoms a few months after starting treatment than those who got a sham treatment—but they were also more likely to have a serious reaction to the injections.

The researchers say most gout patients don't have very severe disease and should not be using the drug.

"The progression in these individuals is extreme," study author Dr. Michael Becker, from the University of Chicago, told Reuters Health. The patients in the study had "gone on to have really severe, on average disabling, (gout), poor quality of life (and) lots of pain."

"This is not a medication to be undertaken in a much larger group of patients," he added.

Of 5 or 6 million people in the U.S. with gout, about three percent do not get better with typical gout drugs, such as Lopurin and Zyloprim, or they can't take the medication for another reason, Becker and colleagues note in the Journal of the American Medical Association. Last year, the U.S. Food and Drug Administration approved Krystexxa, given by injection every other week, for use in those patients.

Gout is a form of arthritis that occurs when uric acid, generally passed out of the body in the urine, accumulates in joints and forms crystals, causing swelling and pain. Krystexxa works by breaking that uric acid down into a form that's more easily passed through the body.

The current report combines data from two drug trials involving 212 patients with chronic gout. Study participants who got the drug injection every two weeks for six months were compared to a group that received injections once a month and a group that got only drug-free placebo injections.

The majority of patients were men in their fifties, on average.

Krystexxa caused uric acid levels to fall quickly, but that response didn't always last. Forty-two percent of patients in the biweekly group and 35 percent in the monthly group still had lowered uric acid six months after starting treatment.

On average, patients who received the drug had a bigger improvement in their general physical function and quality of life compared to those who only got the drug-free injections. And those who got the most frequent drug injections also reported the least pain.

However, more than nine out of ten patients reported at least one "adverse event" including painful gout flare-ups or reactions to the injections, including a few cases of breathing problems. Those reactions were more common in patients taking Krystexxa.

Some patients also reported headaches and nausea.

Becker said doctors could test which patients had stopped responding to the drug and halt treatment to avoid unnecessary risks in people whose gout isn't getting any better.

Krystexxa costs about $5,000 per month. Becker said patients whose symptoms improved with the injections could probably go back on cheaper medications, but it's not clear yet how long most patients would have to get the injections first.

Most patients in the study also had heart conditions, or at least the risk factors for heart disease. Gout often occurs together with obesity and high blood pressure.

Becker said patients who don't respond to Lopurin and Zyloprim have a couple of other medication options (including Uloric, approved by the FDA in 2009), but gout drugs can take up to several years to really kick in and some patients with severe disease can't wait that long. For a number of those patients, Krystexxa may be worth the risks and cost.

"When you have seriously ill people who have no options, 40 percent (of patients getting better) is pretty good," he said. "Gout can be a really serious and disabling disease. With this and other (drugs) that are coming into line for treatment, we can do a good job in virtually all these people, including the sickest."