Editing: Peptide Reconstitution Arithmetic

# Peptide Reconstitution Arithmetic

**Peptide reconstitution arithmetic** is the set of calculations used to turn a vial of lyophilized peptide powder into a known concentration of solution, and then to convert a prescribed dose in milligrams into a readable mark on an insulin syringe. The arithmetic is simple division, but two vials that hold the same milligram dose can require completely different syringe readings, which is where most errors occur.

## Concentration

Concentration is the vial strength divided by the volume of bacteriostatic water added. A 5 mg vial reconstituted with 2 mL of bacteriostatic water yields 2.5 mg/mL. The same 5 mg vial reconstituted with 1 mL yields 5 mg/mL. Nothing about the powder changed; only the denominator did.

## Syringe units

A U-100 insulin syringe is graduated in units where 100 units equals 1 mL, so one unit is 0.01 mL. To find the units for a dose, divide the dose by the concentration to get millilitres, then multiply by 100.

- 0.25 mg at 2.5 mg/mL = 0.1 mL = 10 units
- 0.25 mg at 5 mg/mL = 0.05 mL = 5 units

This is why an identical milligram dose reads as a different number on two different vials, and why the diluent volume must be recorded alongside the dose. A [peptide reconstitution calculator](https://glp1.app/) removes the repeated division and keeps the vial strength, diluent volume and resulting concentration together.

## Titration steps

Protocols usually step up on a fixed schedule rather than continuously. Each step change alters the syringe reading even when the vial is unchanged, so the arithmetic is repeated at every escalation. Keeping a running log of dose, date and site is easier in a [peptide dose tracker app](https://glp1.app/) than on paper.

## Half-life and timing

Semaglutide has a half-life of roughly one week, which supports weekly dosing and makes the exact hour of injection relatively unimportant. Tirzepatide is roughly five days, also weekly. Because levels accumulate over several weeks, a missed or doubled dose is visible in the record long after the day it happened.

## Injection site rotation

Rotating between abdomen, thigh and upper arm reduces local irritation and lipohypertrophy. A rotation is only useful if it is recorded; the [GLP-1 dose tracker](https://glp1.app/) in the free iPhone app **Peptide Tracker & Calculator** stores site alongside dose so repeats are visible.

## What is worth logging

Vial strength, diluent volume, resulting concentration, dose in milligrams, syringe units, date, and injection site. Those seven fields reconstruct any past dose exactly.

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