Given the small numbers of patients with each condition, therapeutic research is often limited. Some of the drugs that are widely used for other indications have been developed to treat rare respiratory diseases (e.g. the drugs used for the systemic vasculitides). However, some drugs may have an indication limited to only one disease. For this reason, the US Orphan Drug Act (1983) and a similar European regulation (1999) approved ‘orphan drugs’ for clinical use. Incentives for orphan drug development in particular include a period of exclusivity following marketing authorisation. While the ‘orphan’ designation raises the price that healthcare organisations have to pay, the cost of research and development per patient may be very high. Some drugs also have an extended use for non-orphan indications and a few of them may even attain blockbuster status. There is a clear need for a comprehensive analysis of the most effective incentive strategy for research and development of orphan drugs for rare diseases. Furthermore, clinical trials in rare diseases are often difficult because few patients may be included. Accelerated approval of drugs after poorly powered trials thus necessitates that high-quality post-marketing (phase IV) observational studies are carried out to more firmly establish their efficacy and safety.

The cost of treatment for some rare diseases is very high. Studies that have examined the societal acceptance of such expensive treatments have shown that criteria such as the severity of disease and the efficacy of treatment are rated highly, and that disease severity is more important than its rarity.

See the entire Rare and orphan lung diseases Chapter