Pfizer Global Manufacturing (PGM) takes a proactive approach to minimizing the environmental impact of its worldwide network
of manufacturing sites and facilities. At the site level, multidisciplinary teams apply green-chemistry principles to process
development to enhance process robustness. Such an approach can reduce emissions, lower the use of hazardous materials, and
enable more process waste to be recycled. Pfizer's improved testosterone process is an example of such an approach.
Figure 1: Molecular structure of testosterone. (FIGURES ARE COURTESY OF THE AUTHORS)
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Pfizer's Kalamazoo, Michigan, manufacturing site has a long history of producing steroids, including testosterone (see Figure
1), for Pfizer's Established Products Business Unit and by Pfizer CentreSource for third-party sale. Used primarily in male-hormone
replacement therapy, testosterone is the registered starting material for testosterone cypionate, the active pharmaceutical
ingredient (API) in Pfizer's DePo testosterone product.
Pfizer improved its testosterone process by developing a green bioprocess route that reduced solvent use, produced less waste,
and eliminated hazardous material use. The goal of the project was to develop an improved process for the testosterone synthesis
that applied Pfizer's Right First Time philosophy (i.e., a scientific approach to continuous improvement to reduce the variation
in processes and optimize them) as well as incorporate the principles of quality by design (QbD), green chemistry, lean manufacturing,
and similar principles to reduce waste, minimize environmental impact, optimize efficiency and speed-to-market, ensure quality,
and maximize operator safety.
Figure 2: Second-generation or greener route to testosterone. (FIGURES ARE COURTESY OF THE AUTHORS)
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The new manufacturing route to testosterone is shown in Figure 2. In the process, the starting material (i.e., androstenedione)
is taken into solution and a proprietary intermediate is prepared, crystallized, and filtered. Then, rather than isolating
a "dried cake," the intermediate is dissolved off of the filter and cycled back into the original vessel, ready for the next
reaction. This scheme is repeated under the final crystallization, which is performed in a workcenter specifically for finishing
APIs.
In addition to requiring high volumes of solvent, the "old" testosterone process generated hazardous wastestreams that had
to be dealt with during each manufacturing cycle. The process-development phase of the improved testosterone process leveraged
existing infrastructure, economies of scale, process telescoping, and systematic application of QbD principles to overcome
this and other challenges. More robust earlier process steps enabled the downstream purifications to use fewer solvents and
relatively less solvent per kilogram to achieve quality equivalent to the previous process material. A big part of the green
process was that it no longer generated a heavy-metals waste stream. These are problematic to dispose of, and eliminating
them is a key benefit. The efficiency of the new chemistry allowed the solvent/product ratio to be reduced in later steps,
which is a welcomed secondary benefit, and one not realized until the development of the new route.
Using a new intermediate and optimizing reagents were also successfully explored during the development process. The new intermediate
enabled the use of a nonmetallic reducing agent, which significantly reduced hazardous waste and improved process safety.
Operating a "cleaner" reaction improved efficiency by 50% in the final recrystallization in regard with solvent usage. These
results combined to reduce overall hazardous waste streams and boost waste-stream recycling.
