How Myobloc (Botulinum Toxin Type B) Is Supplied
Myobloc (rimabotulinumtoxinB) injection is supplied as a clear and colorless to light-yellow solution in single-dose glass vials in three different presentations: 2,500 Units/0.5 mL, 5,000 Units/mL, and 10,000 Units/2 mL. 1
Formulation Details
Myobloc comes as a ready-to-use liquid formulation that requires no reconstitution, unlike some other botulinum toxin products. Each vial contains:
- 2,500 Units/0.5 mL vial: 2,500 Units rimabotulinumtoxinB, 0.235 mg albumin human, 2.9 mg sodium chloride, and 1.35 mg sodium succinate
- 5,000 Units/mL vial: 5,000 Units rimabotulinumtoxinB, 0.47 mg albumin human, 5.8 mg sodium chloride, and 2.7 mg sodium succinate
- 10,000 Units/2 mL vial: 10,000 Units rimabotulinumtoxinB, 0.94 mg albumin human, 11.6 mg sodium chloride, and 5.4 mg sodium succinate 1
Storage and Handling Requirements
Myobloc must be stored under specific conditions to maintain its efficacy:
- Store under refrigeration at 2°C to 8°C (36°F-46°F)
- Keep in the original carton to protect from light
- DO NOT FREEZE
- DO NOT SHAKE
- Discard expired vials according to standard medical waste practices 1
Important Clinical Considerations
Mechanism of Action
Myobloc works by inhibiting acetylcholine release at the neuromuscular junction, causing temporary muscle paralysis. It specifically cleaves the synaptic Vesicle Associated Membrane Protein (VAMP, also known as synaptobrevin), which is essential for acetylcholine release. 2
Potency Information
- One unit of Myobloc corresponds to the calculated median lethal intraperitoneal dose (LD50) in mice
- The specific activity ranges between 70 to 130 Units/ng
- Units of biological activity cannot be compared to or converted into units of any other botulinum toxin product due to differences in assay methods 1
Pharmacodynamics
In patients who respond to treatment, the return of increased muscle tone or saliva production typically starts within 3 to 4 months after injection. 1
Safety Precautions
When administering Myobloc, healthcare providers should:
- Have epinephrine and antihistamine treatments available for all patients receiving treatment
- Ensure caregivers capable of identifying and responding to anaphylaxis observe patients during administration
- Be aware that the risk of anaphylaxis is <2% 3, 2
Myobloc is a specialized medication that requires proper handling and administration by trained healthcare professionals to ensure optimal safety and efficacy for patients.