What you need, and how to mix it

1. 1. Let the vial reach room temperature. Take it out of the fridge about 20 minutes before you start. Wash your hands and clear a clean, flat surface. Cold glass and cold powder both take longer to dissolve.
2. 2. Work out the water volume first. Decide the volume before a needle goes near the vial — it sets your concentration, and you cannot change it afterwards. Use the calculator to pick a volume that puts your dose on an easy number of units.
3. 3. Wipe both stoppers. A fresh alcohol pad on the peptide vial's stopper, another on the water's. Let them air dry — a wet stopper drags alcohol into the vial with the needle.
4. 4. Draw the water. Put the 23G needle on the 3 mL syringe and draw your measured volume of bacteriostatic water. Hold it needle-up and flick any large bubbles to the top, then push them out. Positive first, then draw. The water vial is sealed and not under vacuum, so taking 2 mL out leaves 2 mL of empty space pulling back — the plunger fights you and the stream breaks into bubbles. Push the same volume of air in first, and the water follows the needle out on its own.
5. 5. Add it slowly, down the glass. Angle the needle so the water runs down the inside wall of the vial rather than jetting onto the powder. It usually disappears into the cake within seconds. Some vials draw the water in on their own; others need a slow push. Let the pressure tell you what to do. Many freeze-dried vials are sealed under a partial vacuum: break the stopper with the needle and the vial pulls the water in by itself. Let it, rather than forcing the plunger, which sprays the cake and foams it. Plenty of vials are stoppered at ordinary pressure or under inert gas instead and pull nothing at all — that is normal, not a fault; just push slowly. Going the other way, pushing 2 mL into a small vial with no air taken out raises the pressure inside, so hold it upright and give the plunger a moment before you withdraw, or the last drop sprays back at you.
6. 6. Swirl — never shake. Roll or swirl the vial gently between your fingers, or set it down and wait. Most powders dissolve in one to three minutes. It should end up completely clear, with nothing floating in it.
7. 7. Label it right away. Write the concentration and the date you mixed it on the vial. In a week you will not remember which of two identical vials is which. The calculator prints label text you can copy.
8. 8. Store it cold. A mixed vial lives in the fridge, roughly 2–8 °C, on a shelf rather than in the door where the temperature swings every time it opens. Keep it out of the light. Storage and cold chain covers how long the powder and a mixed vial keep.
9. 9. Draw each dose with a clean needle. Wipe the stopper again every single time. Invert the vial, draw your units with the 1 mL syringe, then hold it needle-up, flick the bubbles to the top and push them out until the plunger reads your number again. Balance it again. Every dose you take out lowers the pressure in the vial, which is why a half-empty vial gets harder to draw from and gives you more bubbles. Push the same number of units of air in before you draw and the draw comes out clean.
10. 10. Put sharps in a sharps container. Never re-cap and reuse a needle, and never put one in household rubbish. A rigid sharps bin costs a few dollars, and the vent needle counts too.

If you are filling a pen cartridge instead of drawing each dose

1. Fill the cartridge, and let the air out as you go. Wipe the cartridge septum, then transfer the mixed liquid into it with the 3 mL syringe. Before you push, put a second, very fine needle through the septum and leave it there — that is your vent. An empty insulin (dosing) syringe is exactly the right thing for it: its 32G needle is the tiny one, and you do not need the barrel, just the needle in the rubber. A cartridge is rigid, so the air has to leave. Glass does not flex, and the air already inside has nowhere to go. With one needle in the septum the pressure climbs as you push, the fill stalls, and the moment you pull the needle out it sprays. The vent needle gives that air a way out — you will hear it hiss — and the liquid goes in smoothly at the pressure it started at.
2. Load the pen, fit a fresh needle, prime it. Pull the vent needle first, then the filling syringe, then screw the cartridge into the pen. Fit a new pen needle for every injection — they are single use. Dial a couple of units and press until a bead appears at the tip, so you know the path is full of liquid and not air.
3. Store it cold. A filled cartridge, in the pen or out of it, lives in the fridge, roughly 2–8 °C, on a shelf rather than in the door where the temperature swings every time it opens. Keep it out of the light. Storage and cold chain covers how long the powder and a mixed vial keep.