Eli Lilly and Co.'s experimental drug to aid digestion may lack sufficient data to support how well it works, according to U.S. regulators reviewing whether the medicine should be cleared for sale.

Solpura capsules don’t appear to help in fat absorption as much as existing drugs made from pigs, Food and Drug Administration staff said Monday in a report.

Outside advisers to the FDA will meet Jan. 12 at the agency’s headquarters in Silver Spring, Md., to review whether the drug should be approved for people with pancreas insufficiency caused by cystic fibrosis, chronic pancreatitis or other conditions.

Lilly got Solpura, chemically known as liprotamase, in its purchase of closely held Alnara Pharmaceuticals Inc. in July for as much as $380 million. The FDA review tests Lilly’s strategy of using small deals to replace products valued at almost half its revenue that are set to lose patent protection by 2013.

“We question whether the applicant has provided substantial evidence of efficacy,” FDA staff said in their review today.

If approved, Solpura would compete with Creon, from Abbott Park, Ill.-based Abbott Laboratories; Pancreaze from New Brunswick, N.J.-based Johnson & Johnson; and Zenpep from Amsterdam-based Eurand NV. Solpura requires fewer pills than other enzyme replacement therapies and may reduce the risk of exposure to viruses because it’s not derived from pigs, Lilly has said.

In cystic fibrosis, a buildup of thick mucus in the pancreas prevents enzymes that break down food from reaching the small intestine. Inflammation or infection of the pancreas can also interrupt the work of these enzymes, leading to vitamin deficiency and malnutrition.

Patents expire next year for Lilly’s top-selling antipsychotic Zyprexa, and in 2013 for the antidepressant Cymbalta and insulin product Humalog. The three drugs are Lilly’s biggest sellers with $9.95 billion in sales in 2009, or 46 percent of the company’s total revenue.