Is 10 mg in 1 mL of 0.9% sodium chloride a sensible presentation for a GLP-1 receptor agonist?

Concretely: 10 mg · 1 mL · 0.9% sodium chloride · a GLP-1 receptor agonist.

I want to decide this in advance so that I am not deciding it under pressure later.

Assume I will follow the plan I write down, so I would like it to be a good one.

What should I decide now, and what should I defer?

Mechanically, this is the one decision in the whole preparation sequence that cannot be revised later, which is why it is worth thirty seconds of arithmetic.

For a dose that will change during titration, choose the volume for the largest intended dose rather than the first, so the whole schedule fits on one barrel without a mid-vial recalculation.

Round to a diluent volume you can measure accurately. Measuring 1.00 mL on a 1 mL syringe is reliable; measuring 1.37 mL on anything is not, and the error propagates into every dose.

Do not change the diluent volume between vials of a titration without recalculating; it is the commonest source of a ten-fold error.

Choose the volume that puts your largest intended dose between 10 and 30 units. Everything else follows.

The honest answer is that a wide range of volumes works and that the extremes at either end cause avoidable problems.

Dead-space loss scales with the number of draws, not with the concentration, so a lower concentration spread over more draws loses proportionally less of the total peptide.

Write the concentration and the resulting units-per-dose on the vial label at reconstitution. The arithmetic that is obvious now will not be obvious at six in the morning three weeks from now.

Nothing here is medical advice, and research-use material is not approved for human use.

Check the vial can physically hold the volume before you draw it up.

Total vial volume is a physical constraint: most 2 mL vials will not take 3 mL of anything.

Vial headspace is the hard constraint. A nominal 2 mL vial typically holds a little over 2 mL to the shoulder; adding 3 mL is not an option and attempting it wastes the lot.

Nominal vial volumes in the standard 2R and 3R glass sizes have published brimful capacities well above the nominal fill, but the usable volume is bounded by the stopper displacement.

Measure a volume you can actually measure. Round numbers, real syringes.

edited 28 Dec 2025 by laminar_bench — added a caveat about sampling

Aim for a dose volume somewhere between about 10 and 30 units on a U-100 barrel and the reading problem disappears.

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.

Write the concentration on the label at reconstitution, in units per dose.

edited 10 Feb 2026 by orla_ferriter — clarified the distinction between purity and content