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Enter the ordered dose and the concentration on the vial label after mixing. See the reconstitution lesson for the full method.
The volume to draw comes from the labelled concentration, which already accounts for powder displacement - the diluent volume does not change the result.
Volume to draw up
After the directed diluent is added, the vial label states a concentration in mg/mL. The volume to draw up is the ordered dose divided by that concentration:
Volume (mL) = ordered dose (mg) ÷ concentration (mg/mL)
The diluent volume is shown for context only; the arithmetic always uses the label concentration, not the diluent volume.
The prescriber orders 1000 mg of ceftriaxone IV. The vial directs: add 10 mL of diluent to yield 100 mg/mL. How many milliliters should the nurse draw up?
Adding a diluent, such as sterile water or normal saline, to a powdered medication to produce a liquid with the concentration printed on the label.
Always use the concentration the label states results after adding the directed diluent (mg/mL). The final volume is often slightly larger than the diluent added because the powder itself adds volume.
Volume (mL) = ordered dose (mg) divided by concentration (mg/mL). For example, a 1000 mg order at 100 mg/mL means drawing up 10 mL.