In Vitro assessment of clarithromycin and erythromycin depletion in the presence of andrographolide using human liver microsomes

Objective Andrographolide is a major bioactive compound of Andrographis paniculata , a medicinal herb widely used in Asia. Previous in vitro studies have reported effects of andrographolide on CYP3A4 expression and activity. However, potential pharmacokinetic interactions with the macrolide antibiotics clarithromycin and erythromycin remain poorly characterized. This study investigated the effect of andrographolide on their in vitro depletion using pooled human liver microsomes (HLMs). Methods Clarithromycin and erythromycin (1 µM each) were incubated in pooled HLMs with or without andrographolide at 2, 10, or 20 μM, corresponding to approximately 10-, 50-, and 100-fold the reported peak concentration (C max ), respectively. Parent-antibiotic depletion was monitored by LC-MS/MS, and depletion rates were estimated by linear regression. Results Andrographolide did not significantly alter clarithromycin depletion at two or 10 µM ( p = 0.1906 and 0.7898), whereas a significant difference was observed at 20 µM ( p = 0.0321). The estimated effects had wide 95% confidence intervals. Erythromycin depletion was significantly altered at all concentrations, with relative differences of 38.5% (95% CI, 28.5%–48.5%), 33.5% (28.6%–38.3%), and 66.2% (57.0%–75.5%) at 2, 10, and 20 μM, respectively (all p < 0.0001). Conclusion Andrographolide exerts a strong, concentration-dependent effect on in vitro erythromycin depletion in HLMs, whereas its effect on clarithromycin depletion is minimal and observed only at supra-therapeutic concentrations (100-fold C max ). Given that effective concentrations exceeded physiological C max levels, clinical relevance remains uncertain. Further investigation is needed to clarify underlying metabolic mechanisms and evaluate in vivo translation.