Apitegromab-mstn 150 mg/3 mL (50 mg/mL) per vial

Basic Info

CAS Number	2278276-46-1
Active Ingredient	Apitegromab (development code SRK-015; US trade name Isembyld), a human IgG4 lambda monoclonal antibody against myostatin pro-forms
Dosage Form	Solution (concentrate)
Specification & Packaging	Strength: 150 mg/3 mL (50 mg/mL) per vial Pack: 1 vial Group: 04 Item No.: 46

Storage & Common Excipients

Storage Conditions	2–8 °C, **do not freeze or shake**. The permitted in-use room-temperature time after removal from the refrigerator follows the label. Once diluted, the solution is generally infused promptly and not stored
Common Excipients	Concentrate for solution: polysorbate 80, polyoxyl castor oil, sodium chloride, water for injection or sterile water; preservative-free; diluted in saline. Confirm against the COA and label

Product Introduction

A **fully human IgG4 lambda monoclonal antibody** that binds the pro- and latent forms of myostatin with high selectivity while **not** binding mature myostatin, thereby releasing the brake on muscle growth. The FDA approved it in September 2026 for **patients aged two years and older with spinal muscular atrophy (SMA) who are receiving SMN2-targeted therapy**. The Chinese name 阿匹特罗单抗 used in the source file is confirmed as the common translated rendering and can be kept, annotated as a transliteration reference

Therapeutic Use

Combination treatment in patients aged two years and older with spinal muscular atrophy (SMA) alongside SMN2-targeted therapy (e.g. nusinersen, risdiplam, onasemnogene abeparvovec), to improve motor function; the precise indication, dosing and combination regimen follow the locally approved label

Mode of Action

Binds myostatin and latent-myostatin precursors with high selectivity and does not bind mature myostatin, lifting the inhibition on muscle growth and increasing muscle mass and function. As a monoclonal antibody it avoids hepatic small-molecule metabolism and has a long clearance half-life supporting dosing once every four weeks

Administration & Monitoring

Intravenous infusion once every four weeks, prepared and infused per the label; monitor motor-function assessments, body weight and muscle strength, falls and fractures; monitor for infusion-related reactions (particularly the first infusion) and anti-drug antibodies

Important Safety Information

Prescription biologic requiring label-conformant preparation and infusion monitoring. **Increased fracture risk, including serious fractures**, requires bone-health assessment; potential effects on reproductive function and possible fetal harm; capability to manage infusion-related and hypersensitivity reactions is required; dosing outside the label in dose or interval is not permitted

Adverse Reactions

Upper respiratory tract infection, vomiting, cough, other viral infections, headache, gastroenteritis and pharyngitis (most common); infusion-related reactions; **increased risk of fractures, including serious fractures**; laboratory abnormalities (mild transaminase elevation, lymphocyte changes); possible effects on reproductive function

Important Risks

Increased fracture risk is the key risk requiring explicit communication; infusion-related and hypersensitivity reactions; potential effects on reproductive function and embryo-fetal development; continued follow-up needed on long-term skeletal growth and pubertal development

Contraindications

Hypersensitivity to apitegromab or excipients; active serious infection (exclude before treatment); pregnancy (may cause fetal harm, so avoid unless necessary); breastfeeding — insufficient data, generally not recommended

Special Populations

The approved population is patients aged ≥2 years with SMA on SMN2-targeted therapy; no approved indication under 2 years; limited geriatric data (the SMA population is predominantly paediatric); women of childbearing potential must be informed of pregnancy risk and use effective contraception; contraindicated in pregnancy

Usage Limitations

Prescription biologic requiring cold chain and dedicated administration management; may only be used in facilities able to monitor infusions; must be diluted and infused exactly as specified (do not dilute with other infusions); strictly prohibited for muscle-building or performance purposes (no such indication); prohibited in competitive sport; actual use must follow the latest approved label

Anti-Doping Testing

Myostatin inhibitors and monoclonal antibodies of this class are currently **not** on the WADA Prohibited List. However, the mechanism of this protein antibody relates to the IGF-1 axis and may indirectly affect GH/IGF-1 test markers, and patients with SMA would not be competing in sport, so this is not a typical anti-doping scenario. Any athlete exposure to this product for any reason must be proactively declared

Product Quality Testing

Identification (anti-idiotype ELISA, SDS-PAGE reduced and non-reduced, CE-SDS), purity and monomer content (SEC-HPLC), glycosylation and charge variants (CEX), potency (cell-based activity assay), concentration, visible particles, sterility and endotoxin, pH and osmolality, anti-drug antibody levels, stability and freeze-thaw/shake tolerance; lot-to-lot consistency studies; COA

Source & Verification Note

CAS 2278276-46-1 confirmed; indication is the FDA approval of September 2026 (patients aged ≥2 years with SMA on SMN2-targeted therapy).