U.S. regulatory agency staff reported that, after studying the application filed by Genzyme Corp for a new version of their Pompe disease drug Myozyme, they were not satisfied with efficacy and safety data and believe more data may be needed before approval.

They specifically referred not only to how this new mass-produced version of the drug may work long-term in adults, but also how the drug worked in children, adding that if approved, the approval should be limited for adult-use only.

The staff documents were released ahead of a Food and Drug Administration advisory panel meeting this week to discuss whether to approve large-scale production of the drug, and a final FDA decision is not expected until the end of November.

The FDA has already approved a version of Myozyme manufactured at a Genzyme facility that uses a 160-liter bioreactor. But Genzyme is seeking U.S. clearance to make the drug, known chemically as algucosidase alfa, at a 2,000-liter plant.

The agency has said it considers the version made at the larger facility to be a different product from that made at the smaller plant because of differences in carbohydrate structure, thus requiring a separate review.

In a study comparing the new version to a placebo, patients experienced side effects similar to the currently available version, including severe reactions and urinary trouble, the FDA said. The staff also noted that the company changed its goals for the drug in the middle of a clinical study.

According to the company, roughly between 5,000 and 10,000 people worldwide have the condition, in which the lack of a certain enzyme causes the heart and other muscles to fail. The condition is inherited and can cause death.

In separate documents, Genzyme said approval for the 2,000-liter version was critical for it to expand capacity and make its drug more widely available. Its experience with the other version as well as clinical trial data show the new version is safe and effective, it said.