A physician order calls for a theophylline oral suspension...

A physician order calls for a theophylline oral suspension to contain 100 $\mathrm{mg}$ of theophylline in $5 \mathrm{~mL}$ of aqueous vehicle. The pharmacist has on hand a $4.5 \%$ aqueous suspension of theophylline. How many $\mathrm{mL}$ of aqueous vehicle should be added to the preparation on hand in preparing the prescribed suspension?

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Key Concepts

Percent Concentration (w/v)

This concept describes a solution’s concentration by expressing the grams of solute present in 100 mL of solution. It is crucial for understanding how much active ingredient is contained per unit volume in a pharmaceutical preparation, enabling accurate adjustments during compounding.

Dilution Calculations

Dilution calculations involve determining how to reduce the concentration of a solution by adding more solvent. This often employs the C1V1 = C2V2 formula, which relates the initial concentration and volume of the solution to the desired final concentration and volume. Such calculations are fundamental in preparing solutions of the correct strength.

Unit Conversions

Unit conversions are essential in pharmacy for translating between various measurement units, for example, converting a percent concentration to mg/mL or determining the volume necessary to deliver a specific dose in mg. Mastery of these conversions ensures accurate medication dosing and safe compounding practices.

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