Pharmacomicrobiomics: The Gut Microbiome as a Critical Variable in Clinical Drug Response

Pharmacomicrobiomics is a rapidly evolving field of pharmacology that addresses a gap largely overlooked by traditional pharmacokinetics: the role of the microbiome in drug response. This review examines the bidirectional relationship between the commensal gut microbiota and pharmacotherapeutic agents, including the activation of prodrugs and the inactivation of drugs with a narrow therapeutic index. In addition, the review highlights the dual role of enterohepatic circulation, demonstrating how microbial enzymes such as β-glucuronidases can influence both life-saving therapeutic efficacy (e.g., mycophenolate) and severe drug toxicity (e.g., NSAIDs and irinotecan). This highly variable balance is particularly susceptible to iatrogenic disruption, most notably antibiotic-induced dysbiosis, which can rapidly deplete essential bacterial populations and eliminate important metabolic pathways. Such alterations represent a critical yet often overlooked variable in clinical pharmacology, placing vulnerable patients at an increased risk of adverse outcomes. To realize the full potential of personalized medicine, clinical practice must evolve to incorporate the microbiome into pharmacological decision-making. Integrating baseline microbial profiling, also known as metabotyping, alongside traditional pharmacogenetic testing, together with proactive adjustment of therapeutic drug monitoring during periods of antibiotic therapy and dysbiosis, represents an important step toward recognizing the gut microbiome as a dynamic and essential organ of drug metabolism.