Table 3.

Frequency of secondary indications by disease area

Disease group	Number of associated approved drugs	Number of drugs with post-approval indication	Percent with post-approval indication (%)
Neoplasms	22	12	54
Skin and connective tissue disease	19	9	48
Digestive system diseases	12	5	41
Musculoskeletal diseases	10	4	40
Endocrine system diseases	8	3	38
Respiratory tract diseases	9	3	33
Nutritional and metabolic diseases	18	6	33
Pathological conditions, signs and symptoms	7	2	29
Hemic and lymphatic disease	11	3	27
Nervous system disease	52	14	26
Infections	27	7	25
Cardiovascular disease	28	7	25
Immune system diseases	13	3	23
Female urogenital diseases and pregnancy complications	14	3	21
Chemically induced disorders	5	2	20
Male urogenital diseases	17	3	18
Stomatognathic diseases	1	0	0
Eye diseases	5	0	0
Congenital, hereditary diseases, and neonatal and abnormalities	8	0	0
Wounds and injuries	2	0	0

Drugs indications are extracted from FDA database. Each indication is matched with related USA National Library of Medicine Drugs Category. Data are drugs approved by FDA after 1997