innovative drugs (NMEs) approved by FDA and 31 percent of the innovative biologics (Tufts Center, 2010).
Oncology drugs dominate orphan drug approvals, accounting for 36 percent of approvals from 2000 to 2006 (Coté, 2010). The other categories accounting for more than 5 percent of approvals include drugs for metabolic disorders (11 percent), hematologic-immunologic disorders and neurologic disorders (7 percent each), infectious or parasitic disorders (6 percent), and cardiovascular conditions (5 percent).
Most drug approvals are for a single indication. A notable exception involves human growth hormone, versions of which account for 14 approvals involving 6 unique products (i.e., products that have the same manufacturer and the same ingredients). Among the 346 orphan drugs approved through 2009, there were 279 distinct products (Appendix B).
Among 108 qualifying orphan drugs that were approved under an NDA from 1984 to 1999 and were still available in 2010, 55 percent had generic equivalents on the market that were manufactured by a competing company (Appendix B).
As of early 2009, 33 previously approved orphan drugs were no longer on the market, of which 12 had no chemically identical approved alternative drugs (Wellman-Labadie and Zhou, 2009). In October 2009, a generic drug that was chemically identical to one of the 12 discontinued drugs (chenodeoxycholic acid [Chenix], approved in 1983) received a new orphan drug approval for the same indication (Chenodal, ANDA #091019).
Although the committee heard criticisms that the incentives and processes for promoting orphan drug development have been more effective in stimulating drug development for the more common rare conditions than for very rare conditions, data on orphan designations suggest that approvals are concentrated neither in the higher reaches of the rare diseases prevalence range (100,000 to <200,000) nor at the lowest end of the range (diseases with affected individuals numbering in single or double digits). The median population prevalence for drugs with orphan designations is 39,000 (Coté, 2009). Of 326 products approved before 2009, 83 (25 percent) were for conditions with U.S. prevalence of less than 10,000 patients.12
As discussed in Chapter 1, very low prevalence rare diseases account for a substantial proportion of the conditions for which prevalence information was reported in the 2009 Orphanet prevalence report. Not surprisingly then, data reported by Heemstra et al. (2009) using an earlier Orphanet report (but excluding diseases with prevalence of less than 0.1/100,000) showed that the more common conditions (10/100,000 to 50/100,000) were more likely to have a U.S. or European orphan drug designation than the less common rare diseases.