Table 1. Chemical compound and secondary patents for drugs in sample.

Category	Number (share) of the 432 drugs with patents that have claims in this category	Average of the number of patents per drug with claims in this category, calculated across the 432 drugs ± standard deviation	Number (share) of the 432 drugs with at least one independent secondary patent in this category	Average of the number independent secondary patents in this category per drug, calculated across the 432 drugs ± standard deviation
Chemical compound	278 (64%)	.85±.84	N/A	N/A
Formulation	348 (81%)	1.6±1.4	242 (56%)	.99±1.24
Polymorph, Isomer, Prodrug, Ester, Salts (“PIPES”)	219 (51%)	.74±.91	104 (24%)	.33±.68
Method of use	357 (83%)	1.8±1.7	272 (63%)	1.3±1.6

Legend: Based on the 432 new molecular entities (with at least one patent) approved by the U.S. Food and Drug Administration between 1985 and 2005. Categories are based on authors' coding of the claims in the 1304 patents (1261 distinct patents) associated with these drugs. “Independent” secondary patents are those that do not have chemical compound claims.