Leveraging Buprenorphine and Halofantrine as Tool Molecules to Develop a Novel Semi-Physiologically based Pharmacokinetic Model Accounting for Gastro-Intestinal Lymphatic Absorption and Enabling Cross-Species Translation

Intestinal lymphatic absorption is a crucial alternative to portal uptake for highly lipophilic drugs (log P > 5), bypassing first-pass metabolism. Unlike the portal-hepatic pathway, lymphatic uptake is rarely considered in physiologically based pharmacokinetic (PBPK) models for oral delivery. Our study developed an innovative Gastro-Intestinal (GI)-lymph-PBPK model that includes GI absorption, chylomicron extraction (CE) to rescue drugs from gut extraction (GE), and bypass hepatic extraction (HE). This model introduces CE clearance (CL_CE), competing with GE clearance, to estimate the drug proportion subjected to CE versus GE. PBPK analysis for Buprenorphine revealed extensive GE (0.87) and HE (0.58), explaining the low bioavailability (F%) of 5.28% in rats. Buprenorphine prodrugs activated CL_CE, leading to CE ranging from 0.37 to 0.79, boosting oral F% to 39.9%-79.9% in rats. To translate from rat to human, our model considered species differences in GI transit time, formulation, food-dependent drug dissolution, allometric scaling in CL_CE, and between species variability in gut metabolism. Using Halofantrine, we established an allometric scaling factor for CL_CE at 1.1. Accounting for six times faster human gut metabolism, our model predicted an extremely low oral F% of 0.382% for Buprenorphine in humans. Incorporating the allometric scaled CL_CE competing with the extensive gut metabolism, our model predicted Buprenorphine prodrugs remains effective in enabling substantial absorption boosts, with oral F% estimates ranging from 15.8% to 56.7% in humans. This study highlights the significant potential of GI-lymph-PBPK modeling in predicting intestinal lymphatic absorption and facilitating cross-species translation.