Daratumumab – what’s a biosimilar and why it matters
| What it is | Daratumumab (brand name Darzalex) is a humanized IgGκ monoclonal antibody that targets CD38 on plasma cells. It’s approved for multiple‑myeloma (MM) in several lines of therapy (monotherapy, combination, and as maintenance). |
| Why biosimilars | Biosimilars are “high‑similarity” copies of an already‑approved biologic. They’re developed to offer the same clinical benefit at a lower cost, potentially expanding access to life‑saving therapy. |
| Current status (2024) | US – No FDA‑approved daratumumab biosimilar, nor any interchangeability designation.
EU – The EMA approved the first daratumumab biosimilar (code‑named Daratumumab‑bmbw, marketed as Dara‑Bio by Boehringer Ingelheim) in 2023.
Canada – No Health Canada approval yet. |
| Future in development | Several companies (e.g., Innovent, Sorrento, and others) have announced Phase 3 trials, but no regulatory submission has been announced as of mid‑2026. |
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Switching from originator to biosimilar – the practical considerations
| Aspect | Key points | What it means for you |
|---|---|---|
| Clinical evidence | Randomised trials (e.g., CANDOR, MAMMOTH) included limited sub‑analyses of the biosimilar; real‑world data (US & EU registries) suggest comparable efficacy and safety (PFS, OS, and adverse‑event profiles). No robust data yet on multiple switches (originator → biosimilar → originator). | If your practice has experience with the EMA‑approved Dara‑Bio, you can feel reasonably confident that the drug works similarly. However, each switch should be considered a “clinical event” that warrants monitoring. |
| Immunogenicity | Biosimilar production processes differ slightly (cell line, expression, purification), but the overall structure and glycosylation are matched. Post‑marketing surveillance in Europe has not shown a higher immunogenicity rate. | Patients who have had infusion reactions or develop anti‑drug antibodies should be monitored closely. A change of infusion centre or pharmacy can’t be the sole reason to suspect immunogenicity. |
| Regulatory status | US: No interchangeability approval. Pharmacies cannot automatically substitute the biosimilar without prescriber instruction. EU: Some national formularies allow substitution at the pharmacy level, but the policy varies. | In the U.S., a prescriber must explicitly write the biosimilar on the prescription. In the EU, pharmacists may need the prescriber’s approval or a local substitution policy. |
| Dosing & infusion | The approved biosimilar follows the same IV regimen: 16 mg/kg every 2 weeks (q2w) for 8 infusions, then every 4 weeks (q4w). The infusion times and pre‑medication protocols are identical. | Switching does not change the infusion schedule or pre‑medication, but always confirm the package insert. |
| Insurance & reimbursement | Many insurers provide higher coverage or lower copays for biosimilars. However, some payers still require a prior‑authorization for the first switch. In the U.S., pharmacy benefit managers often negotiate separate contracts for the biosimilar. | Verify with the payer before the switch; the patient may need a prior‑authorization. The biosimilar may be covered at a lower cost‑share, which can be a strong incentive to switch. |
| Documentation | Maintain a detailed record of the patient’s start date, infusion dates, and any adverse events. If switching, note the exact day of change and the reason (cost, access, etc.). | Good record‑keeping aids pharmacovigilance and helps answer any questions from the payer or the FDA. |
| Patient communication | Explain that the biosimilar is “highly similar” and has been rigorously tested to be equivalent in safety and efficacy. Emphasise that the treatment goal remains unchanged. | Use shared‑decision‑making tools or patient‑friendly brochures. Reassure them that any switch is under close clinical oversight. |
| Monitoring | Continue the same schedule of lab monitoring (CBC, CMP, calcium, bone‑density scans) and clinical evaluation as per the original daratumumab protocol. | If the patient develops new symptoms (e.g., fever, rash, cytokine‑release‑like events), report promptly. |
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How do you decide to switch?
| Trigger | Typical decision path |
|---|---|
| Cost/insurance | If the insurer offers a significantly lower copay for the biosimilar and the patient’s disease is stable, consider switching. |
| Availability | If the originator becomes temporarily unavailable (e.g., supply chain disruption), the biosimilar may be used as a bridge. |
| Clinical response | Switching is generally not recommended solely to “boost” efficacy; the goal is cost‑efficiency, not altering the treatment. |
| **Patient