FDA Approves a New Iberdomide (Zenbexus) Combination for Multiple Myeloma

On August 13, 2026, the FDA granted accelerated approval to iberdomide (brand name Zenbexus, from Bristol-Myers Squibb). Iberdomide is an oral medicine taken as part of a combination, alongside three other treatments:

• daratumumab and hyaluronidase-fihj — a monoclonal antibody given as an injection under the skin,
• dexamethasone — a corticosteroid that has been used in myeloma care for years.

An important point to keep straight: the news here is the approval of iberdomide. Dexamethasone is a long-established medicine and was not newly approved — it is simply one part of this combination. The same is true of the other partner drugs; the FDA action is about clearing iberdomide to be used together with them.

The approval is for adults with multiple myeloma who have already received at least one prior line of therapy that included a proteasome inhibitor and an immunomodulatory agent (two common categories of myeloma treatment). In everyday terms, this is aimed at people whose myeloma has relapsed (come back) or become refractory (stopped responding) after earlier treatment — not people who are newly diagnosed and starting their first treatment.

Whether any specific person is a candidate is a decision for their oncology team, based on their treatment history and overall health.

According to the FDA, iberdomide is taken as a 1 mg capsule by mouth once a day, with or without food, on days 1 through 21 of each 28-day cycle. It is combined with the subcutaneous daratumumab-and-hyaluronidase-fihj injection and with dexamethasone tablets on a set schedule within each cycle. The exact timing and any dose adjustments are managed by the prescribing clinician.

The approval was based on a clinical trial called EXCALIBER-RRMM (identifier NCT04975997). In that study, the iberdomide combination was compared against another established myeloma regimen.

The main measure was the rate of MRD-negative complete response — a deep response in which no myeloma cells can be detected in the bone marrow using sensitive testing (MRD stands for "minimal residual disease"). In the trial:

• 41% of patients on the iberdomide combination reached MRD-negative complete response, compared with
• 21% on the comparison regimen.

The difference was statistically significant. A deeper response like this is generally considered a favorable sign, but MRD status is a laboratory marker, not the same thing as a guarantee of how long someone will live or stay in remission.

The FDA can grant accelerated approval based on a measure that is reasonably likely to predict real clinical benefit — in this case, the MRD-negative complete response rate — so that a promising therapy can reach patients sooner. That is different from a standard approval based on longer-term outcomes.

Because of this, continued approval may depend on confirming the benefit in ongoing study. In EXCALIBER-RRMM, longer-term outcomes such as progression-free survival (how long people live without their disease getting worse) are still being evaluated. In short, this is a meaningful new option, and the fuller long-term picture is still being gathered.

The FDA-approved prescribing information for iberdomide carries a boxed warning — the agency’s most prominent safety alert — for:

• Embryo-fetal toxicity (serious risk of harm to a pregnancy), and
• Serious venous and arterial thromboembolism (dangerous blood clots).

Additional warnings noted with the approval include low white blood cell counts (neutropenia), infections, and second (new) cancers. Because of the pregnancy-related risk, iberdomide is available only through a restricted program called the ZENBEXUS Risk Evaluation and Mitigation Strategy (REMS), which sets requirements that prescribers, pharmacies, and patients must follow.

Anyone taking or considering this treatment should review the full safety details and monitoring plan with their healthcare provider. This article is educational and is not a substitute for medical advice.

• It does not mean dexamethasone was newly approved. Dexamethasone is an existing medicine used as one part of the combination.
• It does not mean the treatment is a cure, or that everyone will respond the same way. The trial measured a deep laboratory response in a subset of patients.
• It does not automatically speak to price, insurance coverage, or pharmacy availability. Specialty oncology drugs like iberdomide are typically dispensed through specific channels, and coverage varies by plan.
• It is not a first-line (newly diagnosed) treatment; the approval is for people who have had prior therapy.

If you or a loved one is living with relapsed or refractory multiple myeloma, this approval expands the menu of options an oncology team can consider — but the right choice always depends on individual circumstances. Good questions to bring to an appointment include whether this combination is appropriate given prior treatments, what the monitoring schedule and REMS requirements involve, what side effects to watch for, and how it compares with other available regimens.

A brief note on the supporting medicine in this regimen: dexamethasone is a widely used corticosteroid, and PriceMyMeds maintains a general information page on it for readers who want to understand that specific medication. That page covers dexamethasone as a standalone medicine — it is not about this new cancer combination — but it can be a helpful reference if you simply want to learn more about that component.

Researchers will continue to follow longer-term results from EXCALIBER-RRMM, which will help confirm the benefit of the regimen over time. As with any newly approved oncology therapy, availability through specialty pharmacies, clinical guidelines, and coverage decisions typically take shape in the months after approval. Patients and caregivers can stay informed through their care team and through the FDA’s approved-drugs resources.