Pharmacy Technician Certification Board Practice Exam

How much of a 5 g/20 mL stock solution is needed to prepare 500 mg in a 500 mL IV solution?

1. 0.2 mL

2. 1 mL

3. 2 mL

4. 5 mL

The correct answer is: 2 mL

To determine how much of a 5 g/20 mL stock solution is needed to prepare a 500 mg dose in a 500 mL IV solution, it is essential to understand the concentration of the stock solution and how to relate it to the desired dosage. First, convert the concentration of the stock solution into a more manageable unit. A concentration of 5 g/20 mL can be rewritten as 0.25 g/mL (5 g divided by 20 mL). To work in the same units as the desired amount (500 mg), convert grams to milligrams. Hence, 0.25 g/mL is equivalent to 250 mg/mL. Next, you need to determine how many milliliters of this stock solution is required to achieve the 500 mg dose. Using the formula: Amount needed (mg) = Concentration (mg/mL) × Volume (mL) We rearrange it to find Volume: Volume (mL) = Amount needed (mg) / Concentration (mg/mL) Inserting the values gives: Volume (mL) = 500 mg / 250 mg/mL = 2 mL. Thus, to prepare a 500 mg dose in