In vivo pharmacokinetics and lactic acidosis toxicity of Phenformin mediated by gut microbiota in control and pseudo-germ-free rats.

AIMS: Phenformin, a classic biguanide, was withdrawn clinically due to severe lactic acidosis, while the non-genetic causes of interindividual toxic susceptibility remain elusive. This study aimed to clarify pharmacokinetics and lactic acidosis toxicity of phenformin mediated by gut microbiota. MATERIALS AND METHODS: Antibiotic cocktails were used to build pseudo-germ-free SD rats. HPLC-MS/MS was employed to detect plasma and tissue phenformin levels. RT-qPCR and Western blot were utilized to measure hepatic Organic Cation Transporter 1 (OCT1) and renal Organic Cation Transporter 2 (OCT2) expression. Targeted GC-MS was used to quantify fecal Short-Chain Fatty Acids (SCFAs) contents. In vitro HepG2/HK2 cell assays and in vivo sodium butyrate supplementation experiments validated the regulatory function of butyrate on OCTs and phenformin toxicity. KEY FINDINGS: Gut microbiota depletion reduced phenformin Cmax and AUC, lowered liver/kidney drug accumulation and alleviated lactate elevation, which suppressed hepatic OCT1 and induced renal OCT2 expression. Fecal butyrate positively correlated with plasma lactate, while sodium butyrate directly modulated OCT expression in vitro and aggravated phenformin-induced lactic acidosis in rats. SIGNIFICANCE: This study identified a novel gut microbiota-butyrate-OCT axis that drives phenformin toxic variability, offering a non-genetic mechanistic explanation for biguanide lactic acidosis and potential microbiota-targeted intervention strategies.