Introduction: The World Health Organization's Essential Drug List (EDL) contains first-in-class drugs and subsequent class entrants (follow-on drugs) deemed necessary to combat diseases prevalent throughout the world, with a special emphasis on developing nations. The EDL also includes originally approved and follow-on indications. There are opposing views regarding the value of follow-on drugs and indications. Critics suggest many follow-on drugs and indications offer little or no benefit to patients. Advocates counter that follow-on drugs offer advantages in terms of improved effectiveness, compliance and patient satisfaction. Objective: In order to inform this debate on the value of follow-on drugs and indications we examined the numbers of follow-on drugs on the EDL and the extent to which follow-on indications are recommended. Methods: We identified all 312 drugs on the 14th edition of the EDL, omitting 72 non-pharmaceutical entities. For the 240 pharmaceutical entities we ascertained whether the Food and Drug Administration (FDA) had approved them, and, if so, when each was approved. We chose a validated therapeutic classification system - the United States Pharmacopeia's Model Guidelines for Medicare formulary management - in order to distinguish first-in-class and follow-on drugs on the EDL. Specifically, we selected the formulary key drug type as our benchmark therapeutic class. We assigned each EDL drug to a formulary key drug type. We defined first-in-class drugs as the first in each formulary key drug type, and follow-on drugs as all other drugs in each formulary key drug type. We identified follow-on indications by comparing WHO-listed indications with the original approved indication(s) by the FDA. Finally, we examined the therapeutic rating (priority vs. standard) given by the FDA to follow-on drugs on the EDL. Results: Sixty-three per cent of the EDL drugs were follow-ons; 15% of the indications were follow-on indications. Fourteen drugs were listed in multiple WHO (sub) groupings; and 49% of follow-on drugs were given a priority rating by the FDA. Conclusions: In light of the fact that the EDL only includes drugs and indications deemed essential, the large number of follow-on drugs, follow-on indications, and priority-rated follow-on drugs on the EDL suggest their importance. From a public policy perspective, it may prove counterproductive to erect hurdles that impede follow-on research and development.

Essential drug list, Follow-on drugs, WHO,
Journal of Clinical Pharmacy and Therapeutics
Institute for Medical Technology Assessment (iMTA)

Cohen, J.P, Cabanilla, L, & Sosnov, J. (2006). Role of follow-on drugs and indications on the WHO Essential Drug List. Journal of Clinical Pharmacy and Therapeutics, 31(6), 585–592. doi:10.1111/j.1365-2710.2006.00777.x