Before it gives a decision to ViroPharma's supplemental biologics license application, the Food and Drug Administration has asked the company to conduct an additional clinical study of its experimental angiodema drug Cinryze - the FDA told ViroPharma on Thursday that the placebo-controlled study submitted to support the application "lacked robustness."

The Cinryze drug manufactured by the Exton, Pennsylvannia-based biotechnology company is already approved for use in prevention of hereditary angioedema attacks. The company is now seeking Cinryze's approval as a treatment for hereditary angioedema (HAE) - a life-threatening condition leads to swelling in different body parts like the hands, feet, face and throat.

With Cinryze being in the market only for a few months as a preventive medication for HAE attacks, analyst Steve Brozak of WBB Securities, said that till FDA approves a drug for use in severe attacks of a specified disease, it does not send clear signals about the effectiveness of the drug to the physicians.

On the question of conducting the FDA-recommended additional trial with regard to Cinryze, ViroPharma's CEO Vincent Milano told Reuters that the company was yet to take a decision towards this end.

However, Maxim Group analyst Yale Jen, saying that ViroPharma would likely decide against the additional trials, added: "Why work on something that potentially could have absolutely no reward or very low reward?"