Shares in Savient Pharmaceuticals shot up more than 50% on Friday after it emerged that US regulators consider Krystexxa to be effective at treating the symptoms of gout, which is caused by excess uric acid in the body, despite concerns over the drug’s safety.

Krystexxa (pegloticase) is a recombinant PEGylated form of the porcine uricase enzyme and is designed to lower levels of serum uric acid and treat the symptoms of gout in patients who are unresponsive to or unable to tolerate conventional treatments.

Briefing documents released last week ahead of the US Food and Drug Administration’s Arthritis Advisory Committee meeting tomorrow state that the agency “does not dispute the efficacy of pegloticase”, but that a closer look should be taken at the drug’s safety profile.

CV risk?
The agency’s review of the two Phase III studies submitted by Savient found that: more patients treated with Krystexxa developed serious cardiovascular events than those given a placebo; that a greater proportion exhibited infusion and allergic reactions; and that the majority of patients developed antibodies to pegloticase, with adverse effects on safety and efficacy.

Normally shareholder confidence would likely have taken a serious hit by such news but, in this instance, most of the patients had other cardiovascular risk factors and so it remains unclear whether the events observed during the trials represent a genuine safety signal or expected side effects relating to these underlying factors, the agency notes.

So the safety of Krystexxa will be the main topic at tomorrow’s meeting, and if the drug ultimately wins the seal of approval from the FDA it will be the first uricase product to become available on the US market.