“If formulation science is the Cinderella of drug development, then excipients are the Cinderellas of formulation science”.
R. C. Moreton, Finn Brit Consulting
This chapter assumes some familiarity on the part of the reader with formulation and excipients, but familiarity can breed contempt. Application of Quality by Design requires thinking beyond pharmacopoeial compliance and fixed formulae, to avoid the inevitable quality problems arising from the use of complex ingredients in complex products. Discounting excipient risk as improbable breeds the unexpected “black swans” (see N. N. Taleb, The Black Swan: The Impact of the Highly Improbable, Random House Publishing Group, NY, 2010, 2nd edn). Criticalities and complexity are critically reviewed as contributors to special cause variation. In Quality by Design, excipients are categorised as critical or non-critical but this binary approach has been criticised. An alternative Kano approach is advocated, which more accurately reflects the effects on finished product quality from excipient variability. Not all excipient effects are amenable to experimentation during development, so continuous monitoring throughout the product lifecycle is essential to the control strategy.
“Excipients originate from all around the world, in many different forms, and with many different attributes. Learning about an excipient as if it were your own product is critical to design”