FDA issues "Critical Path Opportunities for Generic Drugs"

May 4 2007

The U.S. Food and Drug Administration (FDA) has issued the "Critical Path Opportunities for Generic Drugs" report identifying many of the unanswered scientific questions that impede the development of generic versions of commonly used drugs.

The report is part of FDA's Critical Path Initiative, established in 2004 to discern what challenges exist in moving a promising drug, biologic or device along the critical path from discovery, or proof of concept, to a marketable product. Solving these challenges will require the expertise and input of many groups, including scientists from universities, patient groups, government, industry, associations and other private organizations.

"This report pinpoints the barriers that are limiting the availability of additional generic drug options," said Gary Buehler, R.Ph., director, FDA's Office of Generic Drugs. "We hope these findings will encourage research collaboration, lower these barriers and accelerate access to safe and effective generic drugs."

Before they can be approved, generic drugs must have the same active ingredient, dosage form, strength, and conditions of use as the brand name drug. The drugs must also be absorbed at the same rate and in the same amount, a concept known as bioequivalence.

While straightforward tests of blood plasma levels are sufficient to demonstrate bioequivalence for most generic drug candidates, these common tests generally are not appropriate for certain drugs, including asthma inhalers, nasal sprays, and topical skin applications such as anti-fungal creams. As a result, few generic versions are available in these product categories, resulting in less competition and higher prices.

For example, generic drug products that contain the ozone-depleting substance chlorofluorocarbon will be withdrawn from the market after 2008. The new report will help ensure FDA has an adequate scientific basis to review inhaler applications that use an alternative, hydrofluoroalkane.

The report also calls for research on new bioequivalence methods tailor-made for each challenging drug class. These include lung function tests and molecular level imaging for inhalation drugs; particle size distribution tests for nasal sprays; and methods for direct measurement of drug delivered to the skin.

In addition, the report highlights possible research projects that might lead to new modeling and simulation tools for drug absorption, drug release and other drug development issues and to alternative methods for seeking waivers from clinical bioequivalence studies.

Last year FDA issued the Critical Path Opportunities Report listing 76 specific scientific projects that, if undertaken, would help modernize the Critical Path sciences. This companion document focuses more narrowly on the scientific challenges unique to the development of generic drugs.