[Orphan drugs].

Diseases lacking in satisfactory therapies, named orphans (over 60% of the known), raise the problem of the availability of new drugs to be discovered and evaluated on toxicological and clinical bases. The estimated cost for the full development of a drug makes it not profitable (and therefore orphan drug) in the case of rare diseases and the typical diseases of developing countries. The USA with the Orphan Drug Act have faced the former, whereas WHO with the "Tropical Diseases Research" programme has faced the latter. Uncommon formulations and dosages of known substances and products no longer marketed as non-profitable are considered orphans drugs as well.