Question

phenytoin comes from the pharmacy as an IV solution of 1000mg/250ml. a loading dose of 700 mg has been ordered. how many millimeters must be given?​

Answer 1

We can write the following proportion between the milligram and milliliters:

$1000\div 250 = 700\div x$

Solving for x, we have

$x=\dfrac{250\cdot 700}{1000}=175$

Intuitively, the original 1000mg/250ml solution tells us that the number of milliliters is one fourth of the number of milligrams.

So, if we want 700mg, we have one fourth of this value for the milliliters:

$\dfrac{700}{4}=175$