Research Dosing Calculations

Accurate concentration calculations are fundamental to reproducible research. Errors in reconstitution math propagate through every downstream measurement — a 2x concentration error means a 2x error in every data point. This guide covers the mathematics of reconstitution, unit conversion, and serial dilution.

Basic formula: Concentration = Mass / Volume. If you reconstitute a 5mg vial with 1mL of BAC water, your working concentration is 5mg/mL (equivalent to 5000mcg/mL or 5000 units per mL when 1 unit = 1mcg).

Unit conversions: 1mg = 1000mcg (micrograms). 1mL = 1cc (cubic centimeter). These are used interchangeably in research contexts. For international units (IU), conversion factors are compound-specific and should reference the manufacturer's COA or published pharmacopeial standards.

Insulin syringe markings: A standard U-100 insulin syringe reads in units from 0-100, where 100 units = 1mL. Therefore, each unit marking equals 0.01mL (10 microliters). When your reconstituted concentration is 5mg/mL, drawing to the 10-unit mark (0.1mL) delivers 500mcg. This relationship — syringe units x concentration / 100 = delivered mass — is the most important calculation to internalize.

Worked example: You have a 10mg vial and want to deliver 200mcg per 0.1mL (10 units on an insulin syringe). Target concentration = 200mcg / 0.1mL = 2000mcg/mL = 2mg/mL. Required BAC water volume = 10mg / 2mg/mL = 5mL. Reconstitute with exactly 5mL, and each 0.1mL draw delivers exactly 200mcg.

Serial dilution: For very low working concentrations (below 100mcg/mL), serial dilution is more accurate than attempting to measure sub-microliter volumes. Prepare a stock solution at a convenient concentration, then dilute using the formula C1 x V1 = C2 x V2. Example: dilute 0.1mL of a 5mg/mL stock into 4.9mL of BAC water to produce 5mL at 100mcg/mL.

Dilution formula: C1 x V1 = C2 x V2 (where C1 is initial concentration, V1 is volume taken from stock, C2 is desired final concentration, V2 is desired final volume). This holds for any consistent unit system. Always verify by back-calculating: C2 should equal (C1 x V1) / V2.

Quality control: Always double-check calculations before proceeding. Write them out. Use a calculator. A single decimal point error can mean a 10x overdose or underdose, rendering an entire experiment's data unusable. When in doubt, reconstitute at a higher concentration and dilute down — it is always easier to dilute than to concentrate.