This study is looking at how to dose a drug called **melphalan** to treat a type of cancer called **multiple myeloma**. Multiple myeloma is a blood cancer that affects plasma cells in the bone marrow. Patients will receive high doses of melphalan through an IV (a tube that goes into your vein) before they have a **stem cell transplant**. A stem cell transplant helps replace damaged bone marrow. The study will check how patients react to different doses of melphalan and how it affects their blood cells. This is a **Phase I trial**, meaning it’s in the early stages of testing. The study will use a special method called **pharmacokinetic analysis** to see how the drug moves through each person’s body, and find the best dose for each patient.

• The study requires multiple follow-up visits over 90 days after treatment.
• Participants must have specific health criteria and be willing to provide informed consent.
• There are potential risks and side effects, so detailed eligibility criteria are in place.