A Study of Colesevelam for Lenalidomide-Associated Diarrhea

Inclusion Criteria: * Memorial Sloan Kettering Cancer Center (MSK) confirmed diagnosis of multiple myeloma * Treatment with single agent lenalidomide maintenance * Patient must be \>/= 18 years of age at the time of informed consent * Experiencing grade 1 or more diarrhea according to the CTCAE 5.0 criteria for at least 4 out of 7 days preceding screening and study inclusion * Scheduled to receive lenalidomide maintenance cyles at MSK * Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests and other study procedures Exclusion Criteria: * Patients with history of bowel obstruction * Patients with serum triglyceride levels \>300 mg/dL * Patients wit history of hypertriglyceridemia-induced panreatitis * Patients with known hypersensitivity to colesevelam or any component to the formulation * Patients currently already receiving a bile acid sequestrant or have previously used bile acid sequestrant drugs for diarrhea and had no benefit * Patients with diarrhea secondary to infection. Stool studies for GI pathogens should be collected prior to starting colesevelam but do not need to be resulted prior to starting Day 1 dose of colesevelam, unless infection is suspected by the treating investigator, in which case (Clostridium difficile PCR when clinically indicated, GI pathogen panel, stool ova and parasites, Giardia and Cryptosporum stool antigen tests will need to be resulted at investigator discretion.)