Peptide Reconstitution Calculator - assumptions and limitations

Assumptions

• Concentration arithmetic (forward and reverse)

  Forward mode is the standard dilution identity C = m / V (concentration = peptide mg / final volume mL). Reverse mode inverts the same identity to solve for the BAC water volume that lands a target dose at a chosen draw size. Both are dimensional - this calculator does not model peptide pharmacokinetics, stability, or protocol guidance.

• Powder displacement default + hint

  Powder displacement defaults to 0 mL because most suppliers don't publish a value. For vials at or above 10 mg the calculator surfaces a soft hint citing the literature-typical 0.7 µL/mg (Bummer 2002; Carpenter & Manning, Rational Design of Stable Protein Formulations, 2002) so users can override under Advanced if appropriate. The default itself is conservative (sub-1% bias on a typical 1 mL reconstitution).

• U-100 syringe units (definitional)

  U-100 insulin syringes are defined by USP <1601> and ISO 8537:2016 as 100 units = 1 mL (so 1 unit = 0.01 mL). The conversion units = draw_mL * 100 is dimensional, not modelled. Confirm against your specific syringe markings before drawing.

• Doses per vial rounds down (conservative policy)

  Doses per vial floors to whole doses based on the peptide amount and target dose. Days of supply counts full doses only - floor is the tightest bound that does not overstate supply. This is a documented rounding policy, not a model.

Safety checklist

Process and labelling reminders that aren't formulas - the calculator does not enforce them, but skipping them is the most common source of real-world drawing errors.

• Label reconstituted vials immediately

  Write the peptide name, final concentration (mg/mL), reconstitution date, and storage location on every vial as soon as the BAC water is added. Many users also note the BAC water lot number. Labelling protects against mix-ups when multiple peptides are reconstituted at the same time.

• Beyond-use dates are out of scope

  This calculator does not determine beyond-use dates, sterility, or stability. Storage life depends on the peptide, the BAC water preservative, refrigeration, and light exposure. Follow your prescribing professional's guidance and the supplier insert.

  Source: USP <797> Pharmaceutical Compounding - Sterile Preparations.

Formulas used

Each output is derived from one of the formulas below. They run client-side, so what you see in the calculator is what the math actually does.

1. 1. Final volume (mL)

   final_volume_mL = bac_water_mL + displacement_mL

2. 2. Concentration (mg/mL)

   concentration_mg_per_mL = peptide_vial_mg / final_volume_mL

3. 3. Draw per dose (mL)

   draw_mL = target_dose_mg / concentration_mg_per_mL

4. 4. U-100 syringe units (estimate)

   units = draw_mL * 100

5. 5. Reverse mode: BAC water needed

   bac_water_mL = (peptide_vial_mg * desired_draw_mL / target_dose_mg) - displacement_mL

6. 6. Doses per vial

   doses_per_vial = floor(peptide_vial_mg / target_dose_mg)

7. 7. Days of supply

   days_of_supply = doses_per_vial * interval_days

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