1 · Your Vial
2 · Your Dose
Your Recipe
| BAC water | Concentration | Units per dose |
|---|
Why does the calculator ask how much water to add? Isn't that the answer?
Both, depending on which mode you're in. There is no single "correct" amount of bacteriostatic water for a vial — the powder dissolves the same in 1 mL or 3 mL. What the water volume changes is how far up the syringe your dose lands. More water spreads the same dose over more units, which is easier to read accurately. Less water means a smaller injection. The milligrams going into you are identical either way.
So the first mode asks what dose you want and how big a draw you'd like, and tells you the water. The second assumes you already mixed the vial and just need the units.
More water doesn't make the dose weaker?
No. Adding more water dilutes the concentration, so you draw a larger volume to get the same milligrams. Dose is milligrams, not units. A 2 mg dose is 2 mg whether that's 10 units or 30 units.
What is bacteriostatic water, and can I use something else?
Bacteriostatic water is sterile water containing a preservative (usually benzyl alcohol) that allows a vial to be entered more than once. Plain sterile water and saline do not contain that preservative. Use whatever diluent the supplying pharmacy specifies — if your label or pharmacy says something different from what you have on hand, follow them, not this page.
Why did my units change when I opened a new vial?
Because concentration depends on the vial's mg and how much water went in. A new vial at a different strength, or mixed with a different amount of water, changes what one unit delivers — even though the syringe looks identical. This is the most common cause of accidental over- and under-dosing. Recalculate for every new vial, and label the vial with its concentration.
What do "units" actually mean?
Units are a volume marking on an insulin syringe, not a dose. On every U-100 insulin syringe, 1 unit = 0.01 mL. How many milligrams sit in one unit depends entirely on your concentration, which is why two people with identical vials can have completely different unit numbers for the same dose. Always record your dose in mg or mcg — units alone are meaningless without the concentration.
Can I change the ratio in a blend by adding more or less water?
No. In a blend the ratio between the compounds is fixed when it's manufactured. Water changes the total concentration and therefore how many units you draw, but every draw delivers the same proportions. If you need to dose two compounds independently of each other, that requires separate vials.