Elrexfio is not a pill or an infusion. It is an injection, given by a healthcare provider, that connects a patient’s own T cells to myeloma cells. In August 2023 the FDA granted it accelerated approval, according to the International Myeloma Foundation, for adults with relapsed or refractory multiple myeloma who have already received at least four prior lines of therapy. Those must have included a proteasome inhibitor, an immunomodulatory agent and an anti-CD38 monoclonal antibody.
The drug, also known as elranatamab-bcmm, is a bispecific antibody. One arm attaches to the myeloma cell through BCMA, a tumor-specific antigen on its surface. The other grips a nearby T cell through its CD3 antigen and activates it. The T cell then releases cytotoxic granules that kill the cancer cell.
Compared with CAR T-cell therapy
The IMF points to one practical difference from CAR T-cell therapy. No T cells need to be collected, engineered and manufactured over several weeks. Elrexfio engages the patient’s T cells directly after injection, so treatment can start sooner.
What the trial showed
In August 2023, Nature Medicine published results from the phase II MagnetisMM-3 study. The patients were heavily pretreated, and many had poor prognostic features at the outset. The study found deep and durable responses with a manageable safety profile.
Patients got subcutaneous injections of 76 mg once a week after step-up doses of 12 mg and then 32 mg during the first week. Those responding persistently after 6 cycles moved to dosing every 2 weeks. In cohort A, who had not had earlier BCMA-directed therapy, the overall response rate was 61%, and 35% or more reached a complete response. Fifty patients were switched to the every-two-weeks schedule, and 40 improved or kept their response for at least 6 months.
With extended median follow-up of 17.6 months, presented at the American Society of Hematology meeting in December 2023, median progression-free survival was 17.2 months. Median duration of response had not been reached. The IMF says these findings match the earlier phase I MagnetisMM-1 study.
Dosing and safety
Treatment starts with two step-up doses in Week 1, on Days 1 and 4. About an hour before each step-up dose, and before the first full dose on Day 8, patients get premedication: acetaminophen 650 mg, dexamethasone 20 mg and diphenhydramine 25 mg. After that comes 76 mg weekly for 24 weeks, then every 2 weeks for responders, continuing until the disease progresses or toxicity becomes unacceptable. As of July 11, 2025, the FDA approved a less frequent interval for certain responding patients.
Because of its toxicities, the drug is available only through a Risk Evaluation and Mitigation Strategy (REMS) program. The biggest concern is cytokine release syndrome, a potentially fatal immune reaction. The IMF says it is the most frequent side effect of T-cell therapies, though it occurs less often and less severely with bispecific antibodies than with CAR T. Patients may be hospitalized for 48 hours after the first step-up dose and 24 hours after the second, though a doctor may choose outpatient treatment.
Neurologic toxicity, including ICANS, has also occurred and can be severe, life-threatening or fatal. Patients are told not to drive or operate heavy machinery during step-up dosing and for 48 hours afterward. The label also warns of serious infections, neutropenia, raised liver enzymes and harm to an embryo or fetus; effective contraception is advised.
The most common other side effects in MagnetisMM-3 were fatigue, injection site reaction, diarrhea, upper respiratory tract infection, musculoskeletal pain, pneumonia, decreased appetite, rash, cough, nausea and fever. Patients with questions about whether Elrexfio fits their case should talk to their doctor.
