P-glycoprotein (P-gp) is an efflux transporter that limits the intracellular accumulation of xenobiotics, and its activity can be modulated by inhibitors, inducers, and activators. While inhibitors are widely explored to overcome multidrug resistance (MDR), inducers and activators have been proposed as potential strategies in cases of intoxication by reducing systemic exposure to toxic compounds. Previous studies have shown that fiscalins, marine-derived compounds, can modulate P-gp transport activity, with different derivatives exhibiting inhibitory or activating properties. Building on our previous work, in which fiscalin derivatives modulated P-gp activity in an ex vivo rat intestinal model, the present study aims to further validate these findings using in vitro intestinal cell-based systems. In addition, inter-species differences will be evaluated for the first time by comparing rat and human intestinal epithelial cells. This translational approach is expected to clarify the modulatory potential of fiscalin derivatives on intestinal P-gp and provide relevant insights into their application for overcoming MDR or reducing xenobiotic toxicity by limiting intestinal absorption.