Study of Captisol Enabled Melphalan and Pharmacokinetics for Patients With Multiple Myeloma or Light Chain Amyloidosis That Are Receiving an Autologous Transplant.

Inclusion Criteria: * Age ≥18 and ≤ 75 * Patients must have either: * Symptomatic multiple myeloma who have responded to prior induction or salvage chemotherapy (i.e. chemosensitive disease): Patients who are receiving high-dose melphalan and AHCT as part of their initial therapy require at least a partial response (PR) as defined by the International Myeloma Working Group uniform response criteria for MM. Patients who are receiving high-dose melphalan and AHCT as part of salvage therapy require at least a minor response to their last line of therapy to document chemosensitive disease. There is no limit on the number of prior regimens received by the patient. OR * Light chain (AL) amyloidosis who may be newly diagnosed or previously treated * Histologic and serologic findings, reviewed at MSKCC, confirming the diagnosis of multiple myeloma or AL amyloidosis. Standard diagnostic criteria for multiple myeloma will be used, as per the International Myeloma Foundation consensus guidelines * Patients must have at least 3 x 10\^6 CD34+ cells/kg frozen. * Adequate organ function is required, defined as follows: * Serum bilirubin ≤ 2.0 mg/dl * AST, ALT and alkaline phosphatase \< 3 times the upper limit of laboratory normal * Creatinine clearance ≥ 40 ml/min (24 hour urine collection) * LVEF ≥ 45% by MUGA or rest ECHO * Diffusing capacity ≥ 45% (adjusted for hemoglobin) predicted by pulmonary function testing * Performance status (ECOG) ≤ 2 * A willingness to avoid p…