Understanding Dextrose Dilution: A Key Concept for Pharmacy Technicians in Ontario

Dextrose solutions might sound complex, but they're fundamental in the pharmacy world. When preparing medications, sometimes you need to dilute a stronger solution. That’s where the skill of diluting Dextrose comes in, and if you’re gearing up for the Ontario Registered Pharmacy Technician (RphT) exam, getting a grip on these calculations is crucial.

Let's dive into a common question that you might encounter while studying: Dextrose 25% 1000mL is ordered. On hand is Dextrose 70% solution. How much of the 70% Dextrose solution and sterile water will be used to fill this order?

Choices:

• A. 250mL Dextrose 70% and 750mL sterile water
• B. 357mL Dextrose 70% and 643mL sterile water
• C. 424mL Dextrose 70% and 576mL sterile water
• D. None of the above

So, the correct answer is B: 357mL Dextrose 70% and 643mL of sterile water. But how do we figure that out?

Understanding the Formula

To dilute solutions, we frequently use the formula of concentration and volume, which can be expressed as C1V1 = C2V2. In this equation:

• C1 is the concentration of your starting solution (Dextrose 70%).
• V1 is the volume of that solution.
• C2 is the desired concentration (Dextrose 25%).
• V2 is the final volume of the diluted solution (1000mL for our case).

You’re probably wondering how to plug those numbers in, right? Here’s how it works step-by-step:

1. We know V2 is 1000mL, and our goal is to achieve a concentration of 25%.
2. Rearranging the formula gives us V1 = (C2 * V2) / C1.
3. Plug in the numbers: V1 = (25% * 1000mL) / 70%.

Let's do some quick math—don’t worry, it’s not as tricky as it sounds:

• (25 * 1000) / 70 = 357mL.

This means you’re going to need 357mL of the 70% Dextrose solution. Now, if we’re filling a total of 1000mL, how much sterile water do we need?

Total Volume Minus Dextrose Volume

Simple! Just subtract the volume of the Dextrose solution from the total volume:

• 1000mL (Total) - 357mL (Dextrose 70%) = 643mL of sterile water.

Let’s Break Down the Other Options

• Option A: 250mL Dextrose 70% and 750mL of sterile water—this won’t work! If you only use 250mL of the 70% solution, the concentration wouldn’t reach 25%.

• Option C: 424mL Dextrose 70% with 576mL sterile water—this one’s incorrect too, as it uses more Dextrose than needed for the final concentration.

• Option D: None of the above—it’s basically a backup option, but as we pointed out, we have a valid choice in option B!

Now, Why is This Important?

You might be wondering why all these calculations matter. Well, as a pharmacy technician, you’ll be responsible for accurately preparing medications to maintain patient safety and effectiveness. A miscalculation could lead to serious consequences. This is where being precise in your math becomes not just important but essential in your career!

Wrap Up

As you prepare for your RphT exam, remember that these principles are more than just numbers—they’re the backbone of effective and safe pharmacy practice. The next time you’re faced with a dilution problem, take a moment to apply the formula and check your understanding.

Stay focused, practice your calculations, and you’ll not only pass that exam but thrive in your role as a pharmacy technician!