“We see impressive clinical results in less than six months that have never been demonstrated in any other clinical approach for gout patients,” says Paul Hamelin, president of Savient Pharmaceuticals Inc., manufacturer of Krystexxa.

But the medication is not without side effects. In approving the new drug, the FDA is recommending that physicians give patients a corticosteroid and antihistamine before an infusion to prevent the kind of allergic reactions that affected one out of every four clinical trial participants. Mild reactions included skin rashes, hives, shortness of breath, chest discomfort, redness and itching. Severe reactions included wheezing, lip or tongue swelling, changes in blood pressure and anaphylaxis cases. The FDA says no one died in the clinical trials from these reactions, but stresses they have the potential to be life-threatening.

“Reactions to the infusion occurred relatively frequently,” according to the e-mail from FDA spokespersons. “More severe, potentially life-threatening, allergic reactions occurred in about one in every 20 patients.

The FDA says other side effects include nausea, vomiting, constipation and chest pain. Krystexxa wasn’t tested on patients with congestive heart failure, so the FDA urges caution in giving it to patients with that condition.

Hyon Choi, MD, DrPH, professor of medicine at Boston University School of Medicine says this drug definitely has a role for those patients who fail to get a benefit from conventionally available gout medicine, such as allopurinol. But he says patients need to be aware of the challenges that will come with it too, especially the fact that some won’t tolerate it well.

“The problem is this is a foreign protein so people tend to develop antibodies so it loses efficacy or people develop hyper sensitive reactions,” Dr. Choi says. “Some people lose the efficacy after a few treatments and those people won’t get a benefit. But a lot of people do. But it does involve IVs, physician visits and it is costly, more than the regular oral pills. So it is useful for certain segments of gout patients, but not all of them.”

The FDA initially declined approval of the company’s drug, citing concerns about the proposed changes to the manufacturing process.

In clinical trials, 1 out of 4 patients receiving pegloticase experienced a severe allergic reaction. For that reason, the FDA has advised doctors to prescribe corticosteroids and antihistamine medications before treatment to minimize the risks.

Other side effects observed in clinical trials included gout flares, nausea, bruising, irritation of the nasal passages, constipation, chest pain and vomiting.