Bimagrumab (BYM338) · 10 mg
Published- batch · LOT
- B-2026-BIMA-10-001
- Laboratory
- MZ Biolabs
- purity
- 99.92%
- Test date
- 04.08.2026
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Human monoclonal antibody against activin type II receptors (ActRIIA/ActRIIB). Not a peptide — a ~150 kDa immunoglobulin. Blocks the receptor rather than a single ligand, so myostatin, activin A and GDF-11 signalling are shut down together.
Selected size: 10 mg
10 mg analysis published
Titration schedule · reference
The information below is provided from public sources for reference only. It is not advice or instructions for use; products are intended for laboratory research only and not for human consumption.
| Period / condition | Dose | Escalation |
|---|---|---|
| Early studies (phase I) | 210–700 mg IV every 4 weeks | Starting dose |
| Main phase II regimen | 10 mg/kg (max 1200 mg) IV every 4 weeks | Increase if needed |
| Later studies | 10–30 mg/kg IV every 12 weeks | Maximum in this schedule |
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Bimagrumab (BYM338) is not a peptide. It is a fully human IgG monoclonal antibody (~150 kDa) selected from the HuCAL library in a Novartis–MorphoSys collaboration, and it behaves nothing like the short peptides it sits next to — not in size, not in pharmacokinetics, not in how it must be handled.
Most investigational myostatin inhibitors bind the ligand. Bimagrumab acts one level down: it occupies the activin type II receptors (ActRIIA and ActRIIB) so that none of their ligands can dock. That single move silences myostatin (GDF-8), activin A and GDF-11 together — an entire family of negative regulators of muscle mass rather than one molecule. Receptor-level, not ligand-level, blockade is the main reason bimagrumab produced substantially larger increases in muscle mass in studies than myostatin-only agents.
Bimagrumab is one of the few compounds in this category with a large published clinical record, and that record is mixed. It reliably increases muscle mass — demonstrated in sporadic inclusion body myositis, COPD and sarcopenia. But across three separate programmes the added mass did not translate into added function: the phase 2b RESILIENT trial (n=251) missed its primary endpoint of 6-minute walking distance. That is where Novartis ended the muscle-disease effort. Across these same programmes, bimagrumab carried a characteristic side-effect profile — most notably diarrhoea and muscle spasms — that limited tolerability for some participants.
The second chapter is metabolic. In a 48-week phase 2 trial in obesity with type 2 diabetes (n=75), ActRII blockade produced a −20.5% loss of fat mass alongside a +3.6% gain in lean mass. That unusual combination redirected the whole programme: Eli Lilly acquired Versanis Bio in 2023 and the compound became LY3985863. The full read of the data, the limitations and the open questions is in our reference monograph.
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Related compounds are listed under Muscle Growth.
