To determine how many milliliters to administer for the ordered dose of Vistaril, we can use the following formula:
\[ \text{Desired Dose} = \text{On Hand} \times \text{Volume to administer} \]
First, we need to find out how many units are in 1 mL given that there are 1,200,000 units in 2 mL:
\[ \text{Units per mL} = \frac{1,200,000 \text{ units}}{2 \text{ mL}} = 600,000 \text{ units/mL} \]
Now, we know that there are 600,000 units in 1 mL.
Next, we need to find out how many mL correspond to a dose of 600,000 units:
\[ \text{Volume to administer (mL)} = \frac{\text{Desired Dose}}{\text{Units per mL}} = \frac{600,000 \text{ units}}{600,000 \text{ units/mL}} = 1 \text{ mL} \]
You will administer 1 mL of Vistaril for the order of 600,000 units.