Diluent: Definition and Use in Reconstitution
Shows the work. Every example is computed with the formula and numbered steps. For study and exam practice, not for patient care.
Diluent: The liquid added to a powdered drug to reconstitute it, or to a solution to dilute it, of the type and amount the label specifies.
A diluent is the liquid you add during reconstitution. Common ones are sterile water for injection, 0.9% sodium chloride, and bacteriostatic water. Some IM products are mixed with lidocaine to reduce injection pain, but only when the label allows it.
The drug’s label names which diluent to use, how much to add for each route, and the concentration that results. A different diluent or amount gives a different concentration, or may not be compatible at all, so use exactly what the label says.
Order: ceftriaxone 250 mg IM once. Available: ceftriaxone 500 mg vial. The label says: for IM use, add 1 mL of diluent to yield 350 mg/mL.
- Solve for
- Volume to give (mL)
- Vial amount
- 500 mg
- Diluent added
- 1 mL
- Concentration after mixing
- 350 mg/mL
- Ordered dose
- 250 mg
Formula mL = ordered dose ÷ concentration after mixing.
- Adding 1 mL to the 500 mg vial gives 350 mg/mL (from the label).
- mL = ordered dose ÷ concentration.
- 250 mg ÷ 350 mg/mL = 0.7143 mL.
- 0.714286 mL is less than 1 mL, so round to the nearest hundredth: 0.71 mL.
Answer 0.71 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.)