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[Professor Perez] Hey, I'm Professor Perez from Saddleback College. In this example we
are going to do a dosage calculation. So let's get started...right there. Calculate the amount
of amoxicillin to administer. Here we have ordered amoxicillin...450 milligrams...to
be given orally every eight hours. Our dosage strength is 400 milligrams amoxicillin per
5 milliliters. Note...the dose on hand is the same units as the dose ordered. Therefore
no conversion is required. We are going to perform this calculation using three different
methods. Let's go to our first method...the proportion method. Well, what is a proportion?
Remember...a proportion is an equation of two ratios. Let's begin by using our dosage
strength ratio. Here we have the ratio...dose on hand to the dosage unit. And this ratio
is equal to the desired dose to the amount to administer. Now let's go ahead and represent
our quantities using their capital letter abbreviations. So here we have H over Q...is
equal to...D over A. Now remember...we have to solve for A. To do so we are going to cross-multiply
first. So we go...A times H...is equal to...Q times D. And to solve our equation for A,
we will divide both sides by H...giving us the equation A equals...Q times D...divided
by H. Let's go ahead and remind ourselves what these capital letter abbreviations represent.
Remember Q represents the dosage unit...D represents the desired dose and H represents
the dose on hand. Remember, A represents the amount to administer...and that is what we
are trying to calculate here. So let's go ahead and put in our quantities. Our dosage
unit is 5 milliliters. Our desired dose is 450 milligrams. Our dose on hand is 400 milligrams.
Notice here that the milligrams cancel leaving us with the desired units of milliliters.
Performing our calculation we get 5.625 milliliters. Rounding to the nearest hundredth gives us
5.63 milliliters which is said...five and sixty-three hundredths milliliters. Don't
forget to...circle or box your final answer. Now let's go ahead and perform the same calculation
using dimensional analysis which means we are going to a conversion factor. Remember
we're asked to calculate the amount to administer in milliliters. So let's begin with our desired
dose and let's right that as a ratio. 450 milligrams to 1. Now we need to convert these
milligrams to milliliters using a conversion factor. And the information for the conversion
factor is going to come from our dosage strength. But notice here...we put the dose on hand
in the denominator because we want those milligrams to cancel. In the numerator we place our dosage
unit. And notice...milligrams cancel leaving us with units of milliliters. Once again...performing
our calculation we get 5.625 milliliters which gives us five and sixty-three hundredths of
a milliliter rounded to the nearest hundredth. And again always circle or box your final
answer. Now notice here...the amount to administer is equal to the desired dose times the dosage
unit divided by the dose on hand. Well this gives us a formula to use. And that takes
us to our final method for calculating the amount to administer in this example. It's
called the formula method. So what is our formula? Well, the amount to administer is
equal to the desired dose times the dosage unit divided by the dose on hand. This is
what we saw in the previous example. And so...let's represent our quantities using their capitol
letter abbreviations. Here we have A is equal to D times Q divided by H. Representing the
D as a fraction we simply place it over 1. Multiplying the fractions together gives us
our formula for the amount to administer. A is equal to D times Q divided by H. So let’s
use this formula to perform this calculation. Let's replace D with 450 milligrams...remember
that's out desired dose. Our dosage unit Q is 5 milliliters. And our dose on hand H is
400 milligrams. Notice once again milligrams cancel...leaving us with the desired units
of milliliters. Performing our calculation we get 5.625 milliliters. Rounded to the nearest
hundredth we get 5.63 milliliters which is properly said as five and sixty-three hundredths
of a milliliter. Don't forget to circle or box your final answer and always remember
to do that homework. And don't forget...always...say yes to homework...and no to drugs. We'll see
you all again soon!