Erosion of the scope of the Orphan Drug Act in the United States

The Orphan Drug Act provides incentives for drug development in patients with rare diseases. To qualify for benefit under the Act, Congress imposed a prevalence limit of 200 000 patients in the United States. Assuming disease prevalence to be constant, the number of rare diseases that qualifies under the Act is gradually declining because the population is growing. The maximum prevalence for a qualifying disease can be estimated by comparing the 200 000 patient limit with population estimates provided by the United States Census Bureau. Among a sample of diseases with investigational drugs that have achieved Orphan Drug Designations in the past, many are too rare for this erosion to have practical effect. However, for several diseases, disqualification under the Act is likely in the medium term, and there is one example (bladder cancer) that became disqualified about 10 years ago. There are invidious implications for both pharmaceutical companies and patients. Some ways to revise the law, e.g. providing Food and Drugs Administration with authority to improve the regulations, or index-linking numbers of affected patients to the national population, are suggested.