DIY reconstitution math — 10mg vial + 2mL bac water, someone double check my numbers
33 posts
Want a sanity check before I inject. First time reconstituting.
10mg sema vial. Adding 2mL bacteriostatic water. Concentration = 10mg / 2mL = 5mg/mL.
For 0.25mg dose: 0.25 / 5 = 0.05mL = 5 units on a U-100 insulin syringe. For 0.5mg dose: 0.5 / 5 = 0.10mL = 10 units. For 1.0mg dose: 1.0 / 5 = 0.20mL = 20 units.
Am I right that the U-100 insulin syringe '10 units' mark = 0.10mL? I keep seeing conflicting stuff online where people conflate 'units' of insulin vs units on the syringe as a volume measure.
Also: how long is the 10mg vial good for reconstituted in the fridge?
8 Replies
45 posts
Math is correct. U-100 insulin syringe: '100 units' = 1mL by volume. So 10 units = 0.10mL. Your numbers are right.
33 posts
@the_stats_guy @protocolwonk thanks both. Doing 2mL because I want the 5mg/mL concentration for easier small-dose draws. If I'd done 1mL I'd have 10mg/mL which makes 0.25mg = 2.5 units, harder to measure accurately.
50 posts
Reconstituted sema is stable ~28 days refrigerated per manufacturer stability data for the branded product. Research chem versions are not stability-tested, so 28 days is the cautious upper bound. Many users report using longer without issues but you're extrapolating.
97 posts
Concentration choice is correct. 2mL bac water is my standard for 10mg vials — gives you readable measurements at every dose step from 0.25 through 2.4. Don't go more dilute than that or you're pushing 0.5mL IM volumes for high doses.
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43 posts
Note: for Sub-Q injection, even 0.5mL is fine, but anything over that starts to sting / leak. Your 5mg/mL choice keeps every dose under 0.5mL comfortably. Good call.
53 posts
General PSA for this kind of thread: always double-check recon math with a second reference. A decimal-point mistake here is a 10x dose error and sema at 10x dose is a hospital trip. Slow down, check twice.
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212 posts
Math checks out. I did the same recon ratio for my 10mg vial like 6 months ago and yeah, 5mg/mL is way easier to work with than the 10mg/mL people swear by. The U-100 syringe thing confused me too at first, people use "units" for insulin dosing so casually that it bleeds into everything. But yeah you nailed it, 10 units on the syringe = 0.10mL as a volume, totally separate from insulin units. Storage-wise I've kept mine for like 6-7 weeks and it was fine but honestly I'd play it safer and stick to the month window, not worth the guessing game on degradation.
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8 posts
Honestly the math is right but I'd be way more paranoid about that 28 day number. That's for pharma grade stuff in controlled conditions, not some vial sitting in your home fridge next to leftover takeout. I've seen peptides go cloudy way before month 1 was up. If it looks even slightly off, toss it and don't be cheap about it, the cost difference between 4 weeks and 6 weeks of use isn't worth gambling on an infected injection site.