What I have: 20 mg/mL · dulaglutide.
I want to know what the trade-off actually is rather than which option is fashionable.
I would rather have a defensible reason than a marginal improvement.
What does each option buy me, and what does it cost me?
At 20 mg/mL a 0.25 mg draw is 1.3 units on a U-100 barrel and a 2.4 mg draw is 12. Those two numbers decide it, because the concentration is only sensible relative to the smallest and largest volumes you will actually measure with it. 1.3 units is too little of the scale to read honestly — half a graduation is 40 per cent of that dose — so going lower in concentration buys resolution you cannot get back after reconstitution. The other consideration is time: a vial you will finish in a fortnight can be concentrated, and a vial you will draw from for months should be split at reconstitution instead.
The honest answer is that a wide range of volumes works and that the extremes at either end cause avoidable problems.
Worked example. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL. A 0.5 mg dose is 0.5 ÷ 5 = 0.1 mL, which on a U-100 syringe is 10 units. Reconstitute the same vial with 1 mL and the concentration doubles to 10 mg/mL, the same dose becomes 0.05 mL, and you are now reading 5 units instead of 10 — the same dose at half the resolution.
| Appearance | Interpretation | Action |
|---|---|---|
| Intact opaque puck, proud of base | Cycle ran correctly | Proceed |
| Slumped to one side | Shipped before fully dry, or vibration | Usually usable; note it |
| Glassy translucent film | Collapse above glass transition | Test before use |
| Melt-back ring at stopper | Thermal excursion in transit | Test before use |
| No visible cake at all | Very low fill, or nothing there | Weigh it; query the supplier |
Content matters. If the same 10 mg vial assays at 94 per cent content, you have 9.4 mg. In 2 mL that is 4.7 mg/mL, and a nominal 0.5 mg draw of 10 units actually delivers 0.47 mg — a six per cent shortfall that no amount of careful drawing will fix.
U-100 means 100 units per millilitre by definition, so 1 unit is 0.01 mL and volume in millilitres times one hundred gives units. Every conversion here reduces to that.
Measure a volume you can actually measure. Round numbers, real syringes.
edited 24 Jan 2026 by orla_ferriter — removed a claim I could not source
Analytical standards and reagents with traceable certificates. Every quantitative result you read inherits the accuracy of the standard behind it.
Shop standardsAsk PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.