Question

which of the following is the quantity of diluent a pharmacy technician should combine with a 5-ml vial containing 500 mg of azithromycin to achieve a final concentration of 2 mg/ml?
○ 245 ml
○ 120 ml
○ 495 ml
○ 995 ml

Explanation:

Step1: Find total volume for desired concentration

The formula for concentration is $C = \frac{m}{V}$, where $C$ is concentration, $m$ is mass, and $V$ is volume. We know $m = 500\space mg$ and $C = 2\space mg/mL$. Rearranging for $V$, we get $V=\frac{m}{C}$.
$$V=\frac{500\space mg}{2\space mg/mL}=250\space mL$$

Step2: Calculate diluent volume

The initial volume of the vial is $5\space mL$. The diluent volume ($V_d$) is total volume minus initial volume.
$$V_d = 250\space mL - 5\space mL = 245\space mL$$

Answer:

245 mL