Early studies in Yemen⁴ and Uganda⁵ have used some of the core indicators to quantify the impact of essential drugs programmes or of specific interventions within such programmes. Building on this early work INRUD network members undertook a systematic programme to develop, field test and refine drug use indicators. The methodology for collecting the necessary data was tested in Indonesia, Bangladesh and Nepal. In close collaboration with WHO the revised indicators were then used again in Sudan, Uganda, Malawi, Nigeria and Tanzania.

On the basis of these experiences the indicators were limited to those related to facility-specific data, eliminating those which had originally been included to describe the situation in the community or in the country as a whole. An explicit effort was also made to limit the number of indicators, with the intention of defining a core set that could be collected in any health system and would yield the maximum of information with the minimum of effort. Following a review of the revised indicators in 1991 and a second series of field tests in Nigeria and Tanzania in 1992, the present set of indicators was finalized.