Retatrutide Reconstitution Calculation
When reconstituting 20 mg retatrutide in 350 mL bacteriostatic water using a U-100 insulin syringe, you will get 0.00057 mg per unit (or approximately 0.57 micrograms per unit).
Step-by-Step Calculation
Final Concentration
- Dividing 20 mg by 350 mL yields a concentration of 0.057 mg/mL (or 57 micrograms/mL).
U-100 Insulin Syringe Specifications
- A U-100 insulin syringe delivers 0.01 mL per unit marked on the syringe barrel. 1
- Each "unit" on a U-100 syringe represents 1/100th of a milliliter, standardized for U-100 insulin (100 units/mL). 1
Dose Per Unit Calculation
- Multiplying the concentration (0.057 mg/mL) by the volume per unit (0.01 mL) gives 0.00057 mg per unit.
- Expressed in micrograms: 0.57 mcg per unit on the insulin syringe.
Practical Dosing Examples
- 10 units on the syringe = 0.1 mL = 0.0057 mg (5.7 mcg)
- 20 units on the syringe = 0.2 mL = 0.0114 mg (11.4 mcg)
- 50 units on the syringe = 0.5 mL = 0.0285 mg (28.5 mcg)
- 100 units (full 1-mL syringe) = 1.0 mL = 0.057 mg (57 mcg)
Critical Safety Considerations
Reconstitution Volume Warning
- Your proposed dilution of 20 mg in 350 mL is extremely dilute and results in a very low concentration that requires large injection volumes to achieve therapeutic doses.
- Clinical trials of retatrutide used subcutaneous doses ranging from 0.5 mg to 12 mg per week, administered in standard subcutaneous injection volumes (typically 0.5–1.0 mL). 2, 3
- To deliver even the lowest studied dose of 0.5 mg with your dilution, you would need to inject 8.77 mL (877 units across multiple syringes), which is not practical or safe for subcutaneous administration.
Bacteriostatic Water Sterility
- Bacteriostatic water for injection must be sterile and contain antimicrobial preservatives (typically 0.9% benzyl alcohol) to suppress microbial growth during multi-dose use. 4
- Water intended for drug reconstitution in non-hospital settings frequently contains coliform bacteria and multidrug-resistant E. coli when sourced from coolers, bottled water, or boiled tap water. 5
- Using non-sterile or improperly stored bacteriostatic water for injectable drug preparation poses serious infection risk.
Recommended Reconstitution Approach
- Standard pharmaceutical reconstitution for peptide drugs typically uses 1–5 mL of bacteriostatic water to achieve concentrations that allow therapeutic doses in 0.5–1.0 mL injection volumes.
- For 20 mg retatrutide, reconstituting with 2 mL bacteriostatic water would yield 10 mg/mL, allowing a 0.5 mg dose in 0.05 mL (5 units) or a 12 mg dose in 1.2 mL (120 units across two syringes).
- Reconstituting with 4 mL would yield 5 mg/mL, allowing a 0.5 mg dose in 0.1 mL (10 units) or a 12 mg dose in 2.4 mL.
Insulin Syringe Selection
- U-100 insulin syringes are available in 0.3 mL (30 units), 0.5 mL (50 units), and 1.0 mL (100 units) sizes; the 1-mL syringe allows the largest single dose. 1
- Needle length for subcutaneous injection should be 4–6 mm to minimize risk of intramuscular injection, particularly in lean individuals. 1
Storage and Handling After Reconstitution
- Once reconstituted, peptide solutions should be refrigerated at 2–8°C and protected from light to maintain potency. 6
- Reconstituted retatrutide should be used within the timeframe specified by the manufacturer or compounding pharmacy; bacteriostatic water allows multi-dose use but does not extend peptide stability indefinitely.
- Inspect the solution before each use; it should be clear and colorless with no visible particles. 6