A drug developed to treat a rare (“orphan”) disease.

Many diseases are so rare that it is not economically viable for companies to invest in the development of new treatments. Collectively, however, orphan diseases are responsible for a significant burden of disease. Regulatory authorities therefore provide incentives to encourage therapy development for orphan diseases.

To qualify for orphan drug status, a therapy must be targeted at a condition affecting fewer than 200,000 persons in the USA (about six in 10,000 people) or not more than five in 10,000 people in the EU. New antibiotics and other anti-infectives targeting rare but important infections can be granted orphan drug status (e.g. treatment of prosthetic joint infections, or treatment of lung infections in people with cystic fibrosis).