What is a peptide pen? How a reusable pen works

• The pen body holds the mechanism. On the V2 pens ShotLog sells, it is metal.
• The dose knob sets the amount in units, and the window shows the number.
• The piston rod is the black rod inside the body. Each press moves it forward a fixed distance.
• The cartridge holder takes one standard 3 mL glass cartridge. On the V2 Original Style it screws on and sits under the cap. On the V2 New Style it pushes on and twists to lock.
• The cartridge is a glass barrel with a rubber stopper at the bottom and a rubber septum under a crimped aluminum cap at the top.
• The pen needle, or pen tip, is single use. It screws onto the holder, and its short inner end goes through the septum.
• The V2 pens have a cap with an integrated, spring-loaded needle shield at the top. The shield surrounds a standard pen needle and slides back on contact, so you can use the pen with the cap on. Its rim presses against the skin around the site and spreads the pressure over a wider area. That pressure acts as counter-stimulation, which reduces the feel of the needle going in. The needle stays out of sight before and after use.

Turning the dose knob sets how far the piston rod will travel. Pressing the button moves the rod that far. The rod pushes the cartridge stopper, and the liquid in front of it leaves through the needle.

Each click of the knob is one unit. The V2 pens dial 1 to 60 units per press. The 510(k) 80 unit pen, made by Nest Scientific, dials 0 to 80 units in 0.01 mL steps.

Liquid only moves once the rod is touching the stopper. That is why a freshly loaded pen seems to deliver nothing on the first press, and why you prime it first.

1. Fill a cartridge. A 3 mL luer lock syringe moves the liquid in, and a vent needle lets the air out. The fill guide has the steps.
2. Load it. Take the holder off, push the piston rod back into the pen, drop the cartridge in, and put the holder back. See how to load a cartridge and reset the piston.
3. Prime the pen: turn the dose knob to 50 or 60 and press the button until the piston rod meets the cartridge stopper. You may need to repeat this a few times. Do NOT force it: stop pressing once the piston sits gently against the stopper.
4. Clear the air. Screw on a new pen tip, dial 1 and press slowly until a bead of liquid appears. The priming guide covers air bubbles.
5. Dial and press. Set the amount and press the button all the way to 0. On the V2 pens you can do this with the cap on or off, and with the cap on the needle shield covers the pen needle. On the V2 pens, keep holding it for 10 seconds, take the pen tip out, then let go.
6. Finish. Take the needle off, put it in a sharps container, and put the cap back on.

When the stopper reaches the top of the cartridge, it is empty. Start again at step 1 with a new cartridge. If the pen does not behave, troubleshoot your pen.

A reusable pen stays with you. Each use takes one pen needle, and each fill takes one cartridge and one transfer syringe. You read each amount as a number in the window. A U-100 syringe is the whole device and is used once, and you read the amount off lines on the barrel. The pen comparison sets the two side by side.

ShotLog sells four reusable pens. All four take the same standard 3 mL cartridge with a long stopper and the same universal pen needles, so anything you buy for one fits the others. They differ in body, in how far the knob goes per press, and in whether a spring does the pushing. The pen comparison has every spec, and cartridge compatibility covers what fits.

Starting from scratch? The two V2 kits, the Ultimate Research Kit and the Ultimate Research Kit, V2 New Style, put a pen together with five cartridges and a box of 100 needles.