Manufacturing mass intensity: 15 ​Years of Process Mass Intensity and development of the metric into plant cleaning and beyond

The American Chemical Society Green Chemistry Institute (ACS GCI) Pharmaceutical Roundtable is committed to continue to expand and identify elements of small-molecule active pharmaceutical ingredient (API) manufacturing that should be quantified to drive towards more sustainable practices. Process mass intensity (PMI) has been used for over 15 years to evaluate and benchmark progress towards more sustainable manufacturing and quantifies process input mass (e.g. solvent, water, reagents) per mass of output produced. This manuscript introduces Manufacturing Mass Intensity (MMI), a metric that builds upon and expands the scope to account for other raw materials required for API manufacturing. Examples are included to illustrate how quantification of these additional resource requirements will drive more sustainable practices.