Quantifying emerging drugs for very rare conditions.

Background: EU legislation is encouraging pharmaceutical companies to develop drugs for rare conditions, but their often high cost, and potential for long-term administration has led to debate about their affordability and cost-effectiveness.

Aim: To investigate how many drugs are in development for very rare conditions.

Methods: We defined very rare conditions as having a prevalence of <1:50,000, and identified pharmaceuticals in phase II, phase III trials or pre-registration for these conditions using commercial databases.

Results: We identified 42 very rare conditions with at least one drug in late-stage clinical development, with a total of 113 drugs in development (17 for at least two indications). Sixteen drugs were pre-registration, 29 were in phase III development, 65 were in phase II development, one drug was both pre-registration and phase II for different indications and two drugs were in both phase II and phase III trials for different indications.

Discussion: Not all the drugs in development will reach the market, but it is likely that a significant number will do so. Affordability and methods to assess cost-effectiveness will need debate and clear national policy for decision-makers to follow.