Background and purpose: Paclitaxel is a widely used anti-neoplastic agent but has low oral bioavailability due to gut extrusion by P-glycoprotein (P-gp). Oral paclitaxel could be more convenient, less resource intensive, and more tolerable than intravenous administration. Encequidar (HM30181A) is a novel, minimally absorbed gut specific P-gp inhibitor. We tested whether administration of oral paclitaxel with encequidar (oPac+E) achieved comparable AUC to intravenous paclitaxel (IVP) 80mg/m2. Experimental approach: We conducted a multi-centre randomised crossover study with two treatment periods. Patients (pts) with advanced cancer received either oral paclitaxel 615mg/m2 divided over three days and encequidar 15mg orally one-hour prior, followed by IVP 80mg/m2, or the reverse sequence. PK blood samples were taken up to day 9 for oPac+E and day 5 for IVP. Key Results: 42 pts were enrolled; 35 completed both treatment periods. AUC0-∞was 5033.5 +/- 1401.1 ng.h/mL for oPac+E and 5595.9 +/- 1264.1 ng.h/mL with IVP. The geometric mean ratio (GMR) for AUC was 89.5% (90% CI 83.9-95.5). Mean absolute bioavailability of oPac+E was 12%. PK parameters did not change meaningfully after 4 weeks administration of oPac+E in an extension study. G3 treatment emergent adverse events occurred in 7 (18%) pts with oPac+E and 2 (5%) with IVP. 75% of pts preferred oPac+E over IVP. Conclusion and Implications: GMR for AUC was within the predefined acceptable range of 80%-125% for demonstrating equivalence. oPac+E is tolerable and there is no evidence of P-gp induction with repeat administration. With further study, oPac+E is a candidate to replace IVP.