UPDATE 2-US FDA questions Human Genome anthrax drug data

* Some human data in question - FDA

* Agency to decide if more studies needed

* Advisory panel still on for Tuesday

* Shares fall 1.3 pct

(Adds FDA comments, shares)

By Lisa Richwine

WASHINGTON, Oct 26 (Reuters) - U.S. government inspections raised questions about some of Human Genome Sciences Inc's (HGSI.O) data on an experimental treatment for anthrax infection, regulators said on Monday.

The Food and Drug Administration said it will decide if the company needs to run additional animal or human studies of the drug, ABthrax or raxibacumab, after the agency investigates the data and receives advice from a panel of outside experts.

The FDA said it decided to proceed with an advisory committee review of the drug planned for Tuesday. The agency will ask the panel for input on findings from animal studies but will not seek a recommendation on whether the drug should be approved.

"Because the reliability of the human pharmacokinetic data is currently in question, to make a complete judgment about whether raxibacumab should be licensed for marketing is not possible," an FDA statement said.

Anthrax is a bacterium that has been used as a biological weapon. If inhaled, it can cause a potentially fatal lung infection.

ABthrax was developed under the U.S. government's Project BioShield to encourage new drugs and vaccines to fight potential bioweapons. The project was launched after letters carrying powdered anthrax killed five people in 2001.

FDA inspections in recent days "identified issues that raise important concerns about the quality and reliability of human pharmacokinetic data" in Human Genome's application for ABthrax, the agency said.

Pharmacokinetics is the study of the absorption, distribution, metabolism and excretion of a drug. The FDA said the data were essential for determining the proper dose of ABthrax for people.

Discussions with Human Genome about the findings are ongoing, the FDA said. The company did not immediately respond to a request for a comment.

The U.S. government already has ordered 65,000 doses of ABthrax for a national stockpile of emergency medicines.

Human Genome's application for ABthrax relies largely on studies in rabbits and monkeys. FDA rules allow animal tests in lieu of human studies to show the effectiveness of new drugs used to fight certain deadly infections.

The agency said it will ask the advisory panel for input on the "adequacy of the animal efficacy studies used to support approval." Two of the company's four animal studies were inspected and found to be acceptable, the FDA said.

In a summary released last week, FDA reviewers said the drug worked better than a placebo but similar to antibiotics for treating anthrax exposure in animal studies.

The FDA said it may consider reconvening an advisory panel to discuss the drug at a later date.

Human Genome said in July the company would record more than $160 million through the first two quarters of 2009 from government sales of the drug. It is due to receive $10 million more if ABthrax wins FDA approval.

Shares of Human Genome fell nearly 1.7 percent to $19.30 in late-afternoon trading on Nasdaq. The stock has soared nearly 500 percent since July after unexpectedly positive results for an experimental lupus drug that analysts see as a potential blockbuster.

The FDA statement was posted here. (Reporting by Lisa Richwine; Editing by Steve Orlofsky and Richard Chang)