The withdrawal of a multiple sclerosis treatment is likely to lead to even longer product approval times for pharmaceutical companies as pressure mounts on the Food and Drug Administration to improve drug safety, experts say.

The news Monday that one patient died and another developed a serious disease while taking the MS treatment Tysabri (search), made by Biogen Idec Inc. and its Irish partner Elan Corp., is the latest in a series of negative revelations about drugs' safety and effectiveness.

"This is just another black eye for the industry and another black eye for the FDA," said Jason Napodano, an analyst at Zacks Investment Research Inc. "I think we are in for a dramatic slowdown in the approval process as the FDA wants to see more extensive trials and data."

Tysabri was approved under an accelerated review process reserved for drugs that treat patients with especially serious diseases where a lack of other medicines exists. Napodano said the FDA may also be more selective about which drugs get such special treatment.

Experts said the slowdown won't necessarily come through a mandate from FDA officials demanding more data, but could result from independent reviewers working for the agency.

"If you are reviewer on the fence about wondering whether you should ask for more data, this environment will push you to ask for that data," said Daniel Troy, a partner at Sidley Austin Brown & Wood LLP, who was the FDA's chief counsel until last November. "I think there will be more risk averse decision making."

Such a slowdown couldn't come at a worse time for an industry that is already struggling with patent expirations and a decline in the number of new drugs in the pipeline. Conducting more studies will add to costs and potentially delay drugs coming to market.

The average time to win FDA approval for a new drug already has risen to about 17 months from 12.6 months in 1999, according to data from the Pharmaceutical Research and Manufacturers of America.

Analysts said the drugs most likely to suffer under a regime of extreme cautiousness at the FDA are products that represent a new class of medicines or those entering crowded fields where a plethora of treatment option exist.

For example, Bristol-Myers Squibb Co. expects a review of a new diabetes drug sometime this year. It is part of a class of new drugs that had previously raised some safety concerns, so Napodano and others said they wouldn't be surprised if the FDA required more data before giving the medication a greenlight.

Likewise, Pfizer Inc. expects the agency to review its application for inhaled insulin, but some analysts expect that it could encounter some resistance at the agency because of its novel approach. There are already numerous diabetes drugs on the market.

Pfizer declined comment. Bristol-Myers spokeswoman Tracy Furey said the company maintains the drug, called muraglitazar, has a favorable risk to benefit profile.

The safety issue has gathered steam in the last six months with several high profile drugs reporting problems. Merck & Co. withdrew arthritis drug Vioxx (search) from the market because it increased patients risk of heart attack and strokes. Pfizer's competing drugs Bextra and Celebrex were connected to the same side effects. And Eli Lilly & Co. warned doctors that its attention deficit disorder medication Strattera (search) could cause liver problems.

Troy isn't expecting senior FDA officials to make changes in the reviewing procedure because they believe the system works. The FDA didn't immediately return calls for comment.

Earlier this month, the FDA said it would create a new board to oversee the management of drug safety issues. However critics say the board does not go far enough because it not an independent agency and has no real authority.

Additional changes are possible. For example, at the FDA's request the Institute of Medicine will study the effectiveness of how the agency oversees drug safety, with a particular emphasis on learning what additional steps could embraced to learn more about side effects of medicines as they are actually used. The IOM, which advises the government on scientific and technological, hasn't started the study yet and it is unclear when its report will be available.

Pharmaceutical consultant Charlie Beever doesn't believe the FDA needs to slow reviews to improve safety. The vice president with Booz Allen Hamilton Inc. believes the agency needs to get tougher about using some of the tools in its arsenal. For example, in some instances the agency can require companies to conduct post-marketing studies. Critics say the companies don't always follow through on such studies.

"The FDA has authority. The question is to what extent are they applying the authority," Beever said.