Reconstitution: Mixing Powdered Medications, With Example
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Reconstitution: Adding a specified diluent to a powdered drug so it becomes a solution of a known concentration, as the label directs.
Some drugs are supplied as a dry powder because they are unstable in solution. Before giving one, you reconstitute it: add the diluent the label names, in the amount it names, and mix. The label (or package insert) then states the resulting concentration, such as mg per mL.
Calculate the dose from that concentration, not from the diluent volume. The powder itself can add volume, so 10 mL of diluent does not always make 10 mL of solution. Some labels list several diluent amounts, each giving a different concentration: use the one that matches what you added.
The label also says how long the mixed solution stays stable and how to store it; write the date, time, concentration, and your initials on a multi-dose vial.
Order: cefepime 0.5 g IV every 12 hours. Available: cefepime 1 g vial. The label says: for IV use, add 10 mL of diluent to yield 100 mg/mL.
- Solve for
- Volume to give (mL)
- Vial amount
- 1 g
- Diluent added
- 10 mL
- Concentration after mixing
- 100 mg/mL
- Ordered dose
- 0.5 g
Formula mL = ordered dose ÷ concentration after mixing.
- Adding 10 mL to the 1 g vial gives 100 mg/mL (from the label).
- Convert the order to the label's unit: 0.5 g = 500 mg.
- mL = ordered dose ÷ concentration.
- 500 mg ÷ 100 mg/mL = 5 mL.
- 5 mL is exact, so no rounding is needed.
Answer 5 mL
Sources
- DailyMed: drug labeling — U.S. National Library of Medicine
- Clinical Calculations: With Applications to General and Specialty Areas — Elsevier (Kee, Marshall, et al.)
- Calculate with Confidence — Elsevier (Morris)