Yet during the same period, more than 79 per cent of the other drug applications submitted to the European Agency for the Evaluation of Medicinal Products (EMEA) were approved, according to research published in the latest British Journal of Clinical Pharmacology.
"It's difficult to find a balance between the urgent need for drugs for patients with rare diseases and guaranteeing their quality, efficacy, safety and, where necessary, making comparisons with existing drugs" says co-author Professor Silvio Garattini from the Mario Negri Institute for Pharmacological Research in Milan, Italy.
"The lack of reliable methods for evaluating 'orphan drugs' in a small number of people probably explains the poor quality of the applications.
"However, it is clear that less stringent criteria are acceptable for orphan drugs than for drugs for more common diseases, particularly in view of the small number of patients."
Between August 2000, when new legislation came into force, and December 2004, EMEA's Committee on Orphan Medical Products reviewed 255 possible drugs for rare diseases that affect less than five people in 10,000.
Only 18 orphan drugs were approved on the basis of epidemiological data, medical plausibility and potential benefit.
During the same period the EMEA received 193 marketing authorisation applications for non orphan drugs and 153 of these were approved.
"However, ten of the 18 orphan drugs approved were authorised under exceptional circumstances which means that the dosier was not complete and the Committee required additional studies in order to maintain the marketing authorisation" says Professor Garattini.