A total of 303 medicines for rare diseases are in clinical development by US pharmaceutical companies/subsidiaries or awaiting approval by the Food and Drug Administration. The current tally is a marked increase on the 189 and 133 orphan drugs in development in 1992 and 1989 respectively.

More than 160 medicines have been approved for rare diseases in the US since 1995, compared with 108 in the previous decade and fewer than 10 in the 1970s, notes a report published by the Pharmaceutical Research and Manufacturers of America (PhRMA) in association with the Genetic Alliance and the National Organization for Rare Disorders.

This is partly down to advances in medical science, such as better understanding of the molecular and genetic causes of disease, and partly to the tax relief and market exclusivity incentives provided by the US Orphan Drug Act of 1983. As of 10 January, a total of 1,679 medicines had been designated as orphan drugs under the Act. In 2004 there were a record 160 applications for orphan drug status in the US, a 30% increase over the average 124 applications seen in the previous four years.

Rare cancers most active area

The most active area for orphan drug development is rare cancers, such as melanoma, cancer of the blood, and solid tumours of the liver and thyroid. In all, 142 orphan drugs are in clinical trials or awaiting approval for cancer, with a further nine in development for cancer-related conditions (some products are listed in more than one category). Neurological disorders, such as multiple sclerosis and muscular dystrophy, are the next most populous category with 35 orphan drugs in development, followed by infectious diseases like anthrax and West Nile virus (28 medicines in development), and genetic disorders such as cystic fibrosis (26).

According to the National Institutes of Health, there are some 6,000 rare diseases that afflict 25 million Americans. For US purposes, a rare disease is a condition affecting fewer than 200,000 people in that country.

Then rate of approval for orphan drugs in the US has not been matched in Europe, despite the introduction of incentives such as 10 years of market exclusivity through new legislation in 2000.

Last year a paper in the British Journal of Clinical Pharmacology noted that just 12 drugs for rare diseases had been approved in the European Union between 1995 and August 2000, when the orphan drug legislation took effect. Between that point and December 2004, only 18 more orphan drugs were approved, despite the European Medicines Agency designating 255 drugs as orphan medicinal products during that period.