Background: Oraxol is an oral formulation of paclitaxel (PTX) co-administered with the potent, selective, poorly absorbed, P-glycoprotein inhibitor HM30181A (HM) that enhances the absorption of PTX. PK modelling of prior data showed fixed dose administration was feasible. The objectives were to determine the MTD and PK of Oraxol administered as a fixed dose for up to 5 consecutive days. Methods: Eligible pts had advanced solid tumors, ECOG PS ≤ 1 and adequate organ function. The dose escalation utilized the standard 3+3 design (Part 1) and then expanded to enroll additional pts at the MTD (Part 2). The treatment consisted of sequential administration of HM oral 15 mg then PTX oral 270 mg daily while fasting. Dose escalation was achieved by increasing the number of dosing days per week (2 to 5 days per week x 3 weeks then 1-week rest, per 4-week cycle). Pts were monitored for dose limiting toxicity (DLT) during the first cycle for dose escalation/de-escalation decisions. Adverse events (AEs) were assessed per CTCAE v4.03 and response by RECIST v1.1. Results: A total of 34 pts received treatment and were AEs evaluable. Twenty-one of 24 pts in Part 1 were DLT evaluable and 1 DLT (febrile neutropenia) occurred at the 5-day dose level. Ten additional patients were treated at the 5-day dose level in Part 2. The most common (≥30%) treatment-related AEs (TRAEs) were nausea, diarrhea, anorexia and vomiting. Serious TRAEs included febrile neutropenia, pneumonia and dehydration. Pre-medication with steroids/anti-histamines was not required and hypersensitivity reactions were not observed. Partial responses occurred in 2 pts at the 5-day dose level (salivary gland, ovarian cancers). The median Tmax was 1 to 2 hrs. PTX exposure (Cmax and AUC) was comparable following 2-5 days of treatment; with a Day 1 C_max ranging from 147 to 246 ng/mL and AUC_0-8hr ranging from 369 to 800 ng*hr/mL. Plasma levels of HM/metabolite were minimal. Conclusions: The MTD was not reached and the highest planned dose level (HM 15 mg/PTX 270 mg x 5-day) was selected for expansion. Sequential oral administration of HM and PTX achieved clinically efficacious PTX level and showed evidence of anti-tumor activity. Clinical trial information: NCT01967043