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c/reconstitution·posted 2 years ago by u/lurker_for_years

three years of bacteriostatic water threads, summarised so you do not have to read them

Explainer Clean Column ×4 Slow Clap ×3

three years of bacteriostatic water threads, summarised so you do not have to read them. Making the case below, and I expect to lose some of it in the comments.

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

Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.

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.

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

3,301 up / 1,169 down74% upvoted29 commentsid f1l89f30 May 2024

29 comments

13 in this archive, depth 5

best — the order this archive was captured in

u/emil_okwuosa222 points·2 years ago

Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions for a person.

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u/units_not_mgMOD131 points·2 years 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/vial_math_verasyringe math133 points·2 years ago

Careful — that arithmetic is wrong. 20mg in 2mL is 10mg/mL, so 1mg draws to 10 units, not what you wrote.

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u/oskar_ibarra43 points·2 years ago·edited

Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.

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u/cesar_ivaturi55 points·2 years ago

swirl, never shake

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u/lurker_for_yearsOP32 points·2 years ago

30mg into 3mL is 10mg/mL, and 1.5mg of that is 15 units

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u/rasmus_kuipers13 points·2 years ago·edited

Is that a U-100 syringe? The barrel markings change the answer completely.

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u/viktor_erdogan4 points·2 years ago·edited

I would not round that figure. At 5mg/mL a rounding error of two units is a real fraction of the intended amount.

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[removed]30 points·2 years ago

[removed by moderator]

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u/sock_puppet_spotter-19 points·2 years ago

label the vial with the date as well as the concentration

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u/units_not_mgsyringe math72 points·2 years ago

The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests. It is a fraction of a percent and it is dwarfed by fill tolerance.

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u/elin_ferrari105 points·2 years 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/ledger_modmod · vetting0 points·2 years ago

The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests.

Right, and the arithmetic behind it: 5mg in 2mL is 2.5mg/mL, so 0.25mg is 10 units.

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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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