Cartridge or vial and syringe
A pen and cartridge is more accurate for repeat small doses because you count clicks instead of reading a barrel. A vial and syringe is more flexible and cheaper to start. Most people use both: the syringe fills the cartridge, the pen delivers the dose.
They are not really alternatives
The framing of pen against syringe is slightly wrong, because you need a syringe to fill a cartridge anyway. The real question is whether you dose from the syringe or transfer to a cartridge and dose from a pen.
| Pen and cartridge | Vial and syringe | |
|---|---|---|
| Measuring | Count clicks, 0.01ml each | Read graduations by eye |
| Small doses | Precise and repeatable | Hard below about 5 units |
| Needle | 31G × 6mm pen needle | Usually thicker and longer |
| Speed | Seconds once loaded | Draw up every time |
| Setup cost | Reusable pen plus consumables | Syringes only |
| Per dose | About twelve pence | About twenty pence |
| Punctures the vial | Once per cartridge fill | Once per dose |
The accuracy argument
On a 1ml syringe, five units is five hundredths of a millilitre, which is a couple of millimetres of barrel. You are lining up a rubber plunger against a printed line by eye, in whatever light you happen to have. On a pen you count five clicks and feel each one.
There is a second, quieter advantage. A cartridge fill punctures the vial stopper once and then you are done with it for weeks. Dosing straight from the vial punctures it every single time.
When the syringe is the right answer
For a one-off, or for a volume larger than the pen can dial in one go, or when you want to combine things in a single draw. The syringe wins on flexibility.
Questions
- Do I still need syringes if I buy a pen?
- Yes, for filling the cartridge. The pen replaces the measuring and injecting, not the drawing-up.
- Is the pen actually more accurate?
- For small repeat doses, yes, because a mechanical click stop beats a visual estimate. Both are limited by how carefully you reconstituted in the first place.
3ml Glass Cartridge
One 3ml refill cartridge.