Developing oral drug delivery systems using formulation by design: vital precepts, retrospect and prospects.

INTRODUCTION: Over the past few decades, the domain of drug formulations has metamorphosed from the conventional tablets and capsules to advanced and intricate drug delivery systems (DDS), both temporal and spatial. Formulation development of the oral DDS, accordingly, cannot be adequately accomplished using the traditional 'trial and error' approaches of one variable at a time. This calls for the adoption of rational, systematized, efficient and cost-efficient strategies using 'design of experiments (DoE)'. The recent regulatory guidelines issued by the key federal agencies to practice 'quality by design (QbD)' paradigms have coerced researchers in industrial milieu, in particular, to use experimental designs during drug product development. AREAS COVERED: This review article describes these principles of DoE and QbD as applicable to drug delivery development using a more apt expression, that is, 'formulation by design (FbD)'. The manuscript describes the overall FbD methodology along with a summary of various experimental designs and their application in formulating oral DDS. The article also acts as a ready reckoner for FbD terminologies and methodologies. Select literature and an extensive FbD case study have been included to provide the reader with a comprehensive portrayal of the FbD precept. EXPERT OPINION: FbD is a holistic concept of formulation development aiming to design more efficacious, safe, economical and patient-compliant DDS. With the recent regulatory quality initiatives, implementation of FbD has now become an integral part of drug industry and academic research.