genuine question about reconstitution that I am slightly embarrassed to ask
genuine question about reconstitution that I am slightly embarrassed to ask — that is what I am asking, and I have already read the wiki twice.
The failure modes I have actually seen posted here, in order of frequency.
One: reconstituting at a different volume than intended and not writing it down, so the next draw is based on a remembered concentration. Two: treating units as a dose rather than a volume, which breaks the moment the concentration changes. Three: assuming a syringe is U-100 when it is not.
All three are solved by the same two habits — do the arithmetic before the water goes in, and write the result on the glass. Neither costs anything and between them they cover almost every question this board gets.
The arithmetic in full: concentration is mass over volume, so 5mg into 1mL gives 5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1.5mg is 1.5 divided by 5 millilitres, which is 30 units.
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.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
best — the order this archive was captured in
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.
How many mg in the vial and how many mL are you adding?
dead space in the needle hub is real and it is small
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
twice as much water halves the concentration and doubles the units for the same dose
write the concentration on the vial in marker, that is the whole post
Small fix — a U-100 syringe is 100 units per mL. If yours is marked differently it is not U-100 and the whole calculation changes.
This. Showing the working is the fastest way for somebody else to spot the mistake.
Correction: that gives 50 units, not what you have written. 10mg into 1mL is 10mg/mL and the division follows from there.
Spent 5 weeks confused about this until somebody drew the table for me. 10mg, 2mL, 5mg/mL, 0.25mg is 5 units. That is the whole thing.
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.
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
Cosigning the round-number approach.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
Bacteriostatic or plain sterile water?
5mg into 3mL is 1.67mg/mL, and 0.25mg of that is 15 units
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.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
Asked SWB what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
Reminder: this board does maths, not dosing.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
reconstituting at a round concentration makes every later dose easy
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Right, and the arithmetic behind it: 5mg in 2mL is 2.5mg/mL, so 1mg is 40 units.
Is that a U-100 syringe? The barrel markings change the answer completely.
- 1Asked SWB what volume they reconstitute to for their own stability testing…6 comments in this branch · started by u/reflux_report