Background: High-dose melphalan is used in autologous stem cell transplant (auto SCT) for multiple myeloma. Generic melphalan contains Propylene Glycol (PG) as co-solvent. Since FDA approved PG-free melphalan (Evomela ® ) in 2016, there were contradictory reports on toxicity of PG-free melphalan. At Duke, we used PG-free melphalan since 5/2017, but switched to generic melphalan in 11/2017 due to the concern for increased toxicity. We hypothesized that PG-free melphalan is associated with increased toxicity than generic melphalan and conducted a retrospective analysis. Methods: At Duke, myeloma auto SCT is performed as outpatient and patients may be admitted for acute issues. Transplant stay is the period from the transplant day to clinic discharge day. Early response is assessed per IMWG criteria at 60-90 days post-transplant and recorded as present if there was improvement in post-treatment response and absent if response remained the same or worsened. We included all myeloma patients who received the first auto SCT with 200mg/m2 of PG-free melphalan or generic melphalan between 5/1/2017 and 8/31/2018 with necessary lab values to determine ISS and R-ISS stages and treatment responses. Results: Twenty-seven patients received PG-free melphalan and thirty-six received generic melphalan; both groups had similar demographics, performance status and ISS stage (Table 1). There was no statistically significant difference in time to count recovery, toxicities (mucositis, febrile neutropenia), or resource utilization (transplant stay, percentage of admitted patients and length of stay). Treatment response was also similar (33% vs 39%, p-value 0.655). Only 47 patients had accurate R-ISS stages and the results again showed no significant difference in patient characteristics and outcome measures (Table 2). Conclusion: Our auto transplant data for myeloma between 5/1/2017 and 8/31/2018 did not show significant difference in toxicities of PG-free melphalan and generic melphalan. In addition, PG-free melphalan failed to show deeper treatment response.