Botox Dilution Calculation
A 1 mL syringe contains 40 units of onabotulinumtoxinA when 100 units of Botox are reconstituted with 2.5 mL of saline.
Mathematical Calculation
The concentration calculation is straightforward:
- Total units: 100 units
- Total volume: 2.5 mL
- Concentration: 100 units ÷ 2.5 mL = 40 units/mL
Therefore, drawing 1 mL into a syringe yields exactly 40 units of onabotulinumtoxinA 1.
Standard Reconstitution Protocol
The FDA-approved dilution instructions for onabotulinumtoxinA specify that a 100-unit vial should be reconstituted with 2.5 mL of preservative-free 0.9% Sodium Chloride Injection USP to achieve a concentration of 4 units per 0.1 mL (equivalent to 40 units/mL) 1.
Key reconstitution steps include:
- Slowly inject the diluent into the vial and verify vacuum pull 1
- Gently mix by rotating the vial—avoid vigorous shaking 1, 2
- Use within 24 hours after reconstitution when stored at 2°C to 8°C 1
- Discard any remaining solution after single use 1
Important Clinical Considerations
Mechanical stability matters: Aggressive reconstitution techniques using small-diameter needles, multiple injection-aspiration cycles, and violent shaking can reduce potency by up to 42% 2. Use large-diameter needles (30-gauge or larger) and limit manipulation to 2-3 gentle injection-aspiration cycles 2.
Storage limitations are critical: Reconstituted Botox experiences significant potency degradation—a 69.8% loss occurs after reconstitution, immediate freezing, and 2-week storage 3. Even refrigerated storage shows statistically significant degradation after 12 hours 3. The FDA recommendation to discard unused product after 4 hours reflects these stability concerns 4, 3.
Common pitfall: Never refreeze reconstituted Botox for later use, as this dramatically compromises therapeutic efficacy 3.