Microbiome-driven PKs: redefining drug metabolism beyond host enzymes

Introduction: Interindividual variability in drug response remains a significant clinical challenge, leading to therapeutic failure and toxicity. Much of this variability is unexplained by classical host-centric pharmacokinetic (PK) models, highlighting a critical gap in understanding of drug disposition. This review addresses this gap by establishing the gut microbiome as an important determinant of drug fate. Areas covered: This narrative review with scoping approach examines how microbial enzymes affect therapeutics through comprehensive analysis of mechanistic and clinical studies. Key examples discussed include irinotecan, digoxin, and sulfasalazine. We highlight specific situations where the influence of gut bacteria is particularly significant, such as with low-bioavailability drugs and in patients with an ileocolonic anastomosis, where gut bacteria directly impact drug absorption and metabolism. Additionally, we address the limitations of current PK models and explore the potential of new integrated approaches. Expert opinion: We propose that the gut microbiome should be recognized as a ‘fifth pillar’ of PKs. This shift in perspective is crucial for advancing personalized medicine. In this new model, a ‘PK profile card’ integrating microbial, genomic, and clinical data will help guide dosing. We anticipate microbiome analysis to become a standard clinical tool to optimize drug efficacy and safety.