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c/reconstitution·posted 6 months ago by u/niels_roos

mg/mL — 16 things I got wrong before I got it right

Correction Sourced ×7

mg/mL — 16 things I got wrong before I got it right. Not a hot take, just something I have not seen said plainly here.

Wrote the date on the vial as well as the concentration after losing track of which one was opened first.

Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.

The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.

That is everything I have. The rest is opinion and I have tried to keep it out.

4,653 up / 4,109 down53% upvoted12 commentsid 9vga0k18 Jan 2026

12 comments

12 in this archive, depth 5

best — the order this archive was captured in

u/quarter_dose_queenlow and slow0 points·6 months ago

Aim the stream down the wall of the vial rather than into the cake. Reconstitution is a solubility problem, not a mixing problem, and mechanical shear does nothing helpful.

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u/priya_guerrero55 points·6 months ago

If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.

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u/oskar_ibarra14 points·6 months ago

Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no preservative.

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u/units_not_mgMOD41 points·6 months ago

Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.

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u/ines_lindqvist20 points·6 months ago

That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.

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u/bruno_dumitru33 points·6 months ago

Correction: that gives 60 units, not what you have written. 10mg into 3mL is 3.33mg/mL and the division follows from there.

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[removed]30 points·6 months ago

[removed by moderator]

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u/spain_receta24 points·6 months ago

I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.

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u/a1c_arcT2D6 points·6 months ago·edited

Asked WWB what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.

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u/marisol_frisk5 points·6 months ago

Adding more water does not change how much peptide is in the vial. It changes the concentration, which changes the volume you draw for the same amount. That is the entire relationship.

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u/vito_beaulieu4 points·6 months ago

Bacteriostatic or plain sterile water?

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u/mateusz_achebe1 point·6 months ago

label the vial with the date as well as the concentration

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About c/reconstitution

The arithmetic and the technique. Bacteriostatic versus sterile water, reconstitution volume as a concentration choice, converting mg/mL into insulin-syringe units, dead space, swirl-not-shake, stopper coring, and how long a reconstituted vial is actually good for. Math errors get corrected fast and politely.

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