Filed at 7:31 p.m. ET

WASHINGTON (AP) -- More than half of the product research that drug companies routinely promise as a condition of sales approval has yet to begin, the Food and Drug Administration said Thursday.

The good news is that companies are fulfilling commitments on drugs given special fast-track approval to treat life-threatening diseases before there's final proof they really work, the FDA said.

Post-marketing research can be crucial for tracking troublesome side effects and, in the case of fast-track drugs, proving a medicine that alleviates symptoms goes on to lengthen lives.

The FDA has long come under fire for not tracking how much of that promised research actually gets done.

Thursday, the FDA provided a count and a Web site where the public can search how well companies fulfill their commitments. Among the findings:

--Some 60 percent of 1,339 promised post-marketing studies of drugs have not begun, nor have 30 percent of 223 promised studies of biological therapies. Some of those studies have stalled for years.

--Many times, FDA didn't set a deadline. Among those that had deadlines, 2 percent of the drug studies and 8 percent of the biological studies are classified as delayed.

--Among fast-track drugs, half of the promised post-marketing studies already are completed, 28 percent have not begun, and 1.6 percent are officially delayed.

``It shows there's room for improvement,'' by companies and FDA, said Dr. John Jenkins, director of FDA's Office of New Drugs.

Dr. Sidney Wolfe of the consumer advocacy group Public Citizen called the findings grim, saying there are too many unanswered safety questions about big-selling drugs because FDA didn't impose deadlines.

FDA's only recourse if a company balks at a promised study is to pull the drug off the market, which it is reluctant to do. Wolfe wants the FDA to seek congressional authority to impose large fines on companies that stall.

The pharmaceutical industry called the findings ``largely good news.'' The percent of truly delayed studies ``is very small,'' said Alan Goldhammer of Pharmaceutical Research and Manufacturers of America.

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On the Net:

Post-marketing study commitments: http://www.fda.gov/cder/pmc/