Traditional one size fits all pharmacotherapy often yields suboptimal clinical outcomes, preventable adverse drug reactions (ADRs), and significant drug waste, imposing substantial economic and ecological burdens on healthcare systems. This review evaluates the transformative potential of pharmacogenomics (PGx) testing, particularly cytochrome P450 (CYP) gene variants, as a foundation for an ecosystem-centric accountability framework for green pharmacy and links human metabolic variability to specific environmental outcomes. Personalized CYP profiling is shown to minimize the environmental release of unused drugs and potentially ecotoxic metabolites into aquatic ecosystems, in contrast to standard uniform drug use approaches. The limitations of ethnicity-based dosing models, which rely on population genetic variation, are examined in the context of increasing global genetic admixture. It is argued that individual genetic profiling, conceptualized as a PGx-Green Passport, provides a reliable safety standard that accounts for individual differences, thereby enhancing efficiency and well-being in a globalized society. By integrating clinical data, including real-world evidence on hospital utilization, with sustainability frameworks, this review demonstrates that PGx-guided therapy is not only a tool for clinical efficiency but also a fundamental requirement for systematically achieving environmentally sustainable healthcare.

The combination of thiopurine and methotrexate (MTX) is a standard co-therapy regimen for acute lymphoblastic leukemia (ALL). Despite its efficacy, this regimen is constrained by a narrow therapeutic window and considerable inter-individual variability, which heightens the risk of drug-induced liver injury (DILI). MTX-induced metabolic strain further destabilizes cytokine-sensitive thiopurine detoxification pathways during systemic inflammation. Conventional pharmacogenetic (PGx) testing for TPMT and NUDT15 variants is effective in predicting myelosuppression, but often fails to detect hepatotoxicity as an adverse effect, suggesting a clinically significant genotype-phenotype difference. This review examines the molecular determinants of DILI, emphasizing the role of secondary metabolic pathways and transporter dynamics as key modulators of risk. The study describes cytokine-mediated (IL-6, TNF-α) transcriptional suppression of cytochrome P450 enzymes and hepatic transporters (SLCO1B1, ABCC2/4) not merely as secondary modulators, but as the primary determinants of localized, tissue-specific drug exposure through disrupted nuclear receptor signaling (PXR, CAR, HNF4α). This mechanism promotes functional phenoconversion and toxic molecular shunting, leading to increased intrahepatic drug exposure. It synthesizes the current knowledge on the metabolism of thiopurine and MTX, focusing on the genetic and non-genetic factors influencing toxicity and their interactions. The review also critically evaluates the limitations of static PGx-guided dosing. It highlights the need for comprehensive, real-time risk assessment that integrates gene-environment interactions, multi-omics data, and clinical monitoring to improve precision therapy for ALL. This approach combines extended PGx profiling, transcriptomic monitoring, and clinical biomarker assessment to provide a transformative strategy for precision drug delivery.