PURPOSE: Effective treatment of patients with locally advanced pancreatic cancer is a significant unmet clinical need. One major hurdle that exists is inadequate drug delivery due to the desmoplastic stroma and poor vascularization that is characteristic of pancreatic cancer. The local iontophoretic delivery of chemotherapies provides a novel way of improving treatment. With the growing practice of highly toxic combination therapies in the treatment of pancreatic cancer, the use of iontophoresis for local delivery can potentiate the anti-cancer effects of these therapies while sparing unwanted toxicity. The objective of this study was to investigate the impact of formulation on the electro-transport of the FOLFIRINOX regimen for the development of a new treatment for pancreatic cancer. METHODS: Three formulations of the FOLFIRINOX regimen (5-fluorouracil, leucovorin, irinotecan, and oxaliplatin) were generated at a fixed pH of 6.0 and were referred to as formulation A (single drug solution with all four drugs combined), formulation B (two drug solutions with two drugs per solution), and formulation C (four individual drug solutions). Anodic iontophoresis of the three different formulations was evaluated in orthotopic patient-derived xenografts of pancreatic cancer. RESULTS: Iontophoretic transport of the FOLFIRINOX drugs was characterized according to organ exposure after a single device treatment in vivo. We report that the co-iontophoresis of two drug solutions, leucovorin + oxaliplatin and 5-fluorouracil + irinotecan, resulted in the highest levels of cytotoxic drugs in the tumor compared to drugs delivered individually or combined into one solution. There was no significant difference in plasma, pancreas, kidney, and liver exposure to the cytotoxic drugs delivered by the three different formulations. In addition, we found that reducing the duration of iontophoretic treatment from 10 to 5 min per solution resulted in a significant decrease in drug concentrations. CONCLUSIONS: Underlying the difference in drug transport of the formulations was electrolyte concentrations, which includes both active and inactive components. Electrolyte concentrations can hinder or improve drug electro-transport. Overall, balancing electrolyte concentration is needed for optimal electro-transport.