Safety and efficacy of propylene glycol-free melphalan as conditioning in patients with AL amyloidosis undergoing stem cell transplantation

High-dose melphalan is the standard conditioning regimen for patients with AL amyloidosis receiving autologous stem cell transplantation. Conventional formulations require propylene glycol (PG) as a co-solvent and melphalan has limited solubility and chemical stability after reconstitution, with potential risks for propylene glycol-related complications. Captisol-stabilized propylene glycol-free (PG-free) melphalan has been developed with improved solubility and chemical stability. We compared a cohort of patients with AL amyloidosis receiving PG melphalan (n = 96) to those receiving PG-free melphalan (n = 48) as conditioning for autologous stem cell transplantation. Median time to neutrophil and platelet engraftment was the same; 14 days PG melphalan vs 14 days PG-free melphalan, p = 0.73 and 16 days PG melphalan vs 16 days PG-free melphalan, p = 0.52, respectively. Hospitalization rate was similar in both cohorts, 68% PG melphalan vs 58% PG-free melphalan, p = 0.27. All-cause mortality at 100 days was not statistically significant, 3% PG melphalan vs 2% PG-free melphalan, p > 0.99. Overall response rate (ORR) and rates of complete response (CR) were similar (ORR 93% PG melphalan vs 94% PG-free melphalan, p > 0.99 and CR 39% PG melphalan vs 32% PG-free melphalan, p = 0.46). PG-free melphalan showed a comparable safety and efficacy profile to PG melphalan in patients with AL amyloidosis receiving stem cell transplantation.