Objective To explore the differences in the incidence and severity of diarrhea between patients receiving propylene glycol-melphalan (PG-MEL) or propylene glycol-free melphalan (PG-free MEL) pretreatment during autologous hematopoietic stem cell transplantation (AHSCT).

Methods The clinical data of 30 patients who underwent AHSCT with high-dose MEL (HDM) pretreatment at the Department of Hematology, Zhongshan Hospital (Xiamen), Fudan University, from January 2024 to November 2025 were retrospectively analyzed. Patients were divided into the PG-MEL group (n＝15) and the PG-free MEL group (n＝15) according to the formulation. The incidence, onset time, maximum daily frequency, duration, type, and severity of diarrhea were compared between the two groups. Oral mucositis, vomiting, infection, fever, and other related adverse events, as well as hematopoietic recovery, were also observed.

Results The overall incidence of diarrhea was 93.3% in both groups. There was no significant difference in the onset time of diarrhea between the two groups (4.0±2.0 d vs 3.0±2.0 d). Compared with the PG-MEL group, the PG-free MEL group had a higher maximum daily frequency of diarrhea (8 6,14 times vs 6 4,6 times, P＝0.009), a higher proportion of grade 3–4 diarrhea (57.1% vs 14.3%, P＝0.046), and a longer duration of diarrhea (8.0±4.0 d vs 5.0±2.0 d, P＝0.033). No statistically significant differences were observed between the two groups in the incidence of other adverse events such as oral mucositis, vomiting, infection, fever, or neutrophil and platelet engraftment times.

Conclusions PG-MEL and PG-free MEL showed the same overall incidence of diarrhea in AHSCT. However, the PG-free MEL group experienced more severe diarrhea and longer duration. There were no significant differences between the two formulations in other adverse reactions or short-term transplant outcomes.