Accepted answer
Yes, and 25G is the number that makes the case: the gauge scale runs backwards, so 25G is deliberately coarse and the drawing and administering jobs want opposite ends of it. Drawing wants bore — a wide needle empties a vial quickly and does not cavitate as the plunger pulls. Administering wants the opposite, because the hole it leaves is the hole the solution can leak back out of. The cost of doing both with a 25G drawing needle is paid on the stopper: every puncture with a 25G point cuts an annulus of rubber, and the coring risk is worst on the wide end. The cost of swapping is one extra connection and whatever dead space that connection holds — which is a real loss, so measure it rather than assume it is nothing.
Start with the fact that gauge numbers run backwards — a higher number is a thinner needle — which is the source of half the confusion in this tag.
A 30G or 31G needle through a butyl stopper leaves a track that reseals, which is why fine-gauge repeated entry is tolerable and coarse-gauge repeated entry is not.
Concentration and unit conversion at a glance
| Vial | Diluent | Concentration | 0.25 mg | 0.5 mg | 1 mg | 2.5 mg |
|---|
| 5 mg | 1 mL | 5 mg/mL | 5 u | 10 u | 20 u | 50 u |
| 5 mg | 2 mL | 2.5 mg/mL | 10 u | 20 u | 40 u | 100 u |
| 10 mg | 1 mL | 10 mg/mL | 2.5 u | 5 u | 10 u | 25 u |
| 10 mg | 2 mL | 5 mg/mL | 5 u | 10 u | 20 u | 50 u |
| 10 mg | 3 mL | 3.33 mg/mL | 7.5 u | 15 u | 30 u | 75 u |
Units are U-100 insulin units, where 1 unit = 0.01 mL. Divide dose by concentration for millilitres, then multiply by 100.
Mechanically, for injecting, 29G to 31G is the usual range and the difference in perceived discomfort between them is small. Needle length matters more than gauge for comfort at these volumes.
Needle gauge to outer diameter correspondence is standardised and published; the inverse relationship between gauge number and diameter is the reason for the counter-intuitive labelling.
If a solution will not draw through a 25G needle, the problem is the solution rather than the needle.
Length affects comfort more than gauge does at these volumes.
Would this be different for a peptide that foams? Mine does and I have never known why. – meniscus_film 7 months ago 8Same experience here, different supplier. – RP_C18 6 months ago add a comment