Understanding Aliquots

A pharmacy technician receives a

prescription.

It is for 15mg of Augmentin in 30ml cherry syrup.

In order to weigh something that small we have to use the aliquot method.

First we have to know the steps for Aliquot measuring

Steps for Weight Aliquot Measuring 1. Calculate least weighable quantity based on

balance sensitivity and permissible margin of error.2. Determine the amount of the ordered drug that

you will actually weigh out.3. Determine the amount of diluent.4. Combine the drug and diluent measured in steps

2 & 3 and mix them well.5. Determine the amount of mixture needed to

provide the originally ordered amount.

Step 1

A class A balance has a sensitivity of 6mg with a 5% margin of error. To figure out the least weighable quantity (LWQ) the equation is:100 x sensitivity = LWQ% margin of error

Least Weighable Quantity

100 x 6 mg = ? mg5

What is the least amount of drug we can weigh?

240 120

Not Quite…Try Again!

Congratulations!Good Job! So the least amount of Augmentin

we can weigh is 120 mg.

How are we going to weigh 15mg?

Lets go to Step 2

Step 2Determine the amount of the ordered drug that you will actually weigh out. This amount must be equal to or greater than the LWQ.

To calculate the amount of drug to weigh out, multiply the amount of drug ordered by a whole number until you have an amount equal to or greater than the LWQ. This number is called a factor and it can be any number you want. Just remember we want to keep it as close to the LWQ as possible.

Multiply the amount by a number to get it close to 120 mg.

What factor can you multiply 15 mg to give you a number close to or equal to 120 mg?

15 mg x ? = ?

10 8

Not Quite…Try Again!

Congratulations!

So when we multiply our 15 mg by a factor of 8 we get 120 mg. Which is exactly our LWQ. This is important because it will cut down on waste later on. Now lets figure out how much diluent we need.

Step 3To determine the amount of diluent we multiply the LWQ by our factor.

LWQ = 120 mg

Factor = 8

120 mg x 8 = ?

720 960

Not Quite…Try Again!

Congratulations!

120 mg x 8 = 960 mgSo we are going to weigh 960 mg of diluent and 120 mg of Augmentin.

Lets go to the next step!

Step 4Combine the drug and diluent measured in steps 2 & 3 and mix them well.

Step 5Determine the amount of mixture needed to provide the originally ordered amount.

We will use the following equation to figure out what part of the mixture will contain our 15 mg of Augmentin.

x mg mixture=amount of drug ordered x total mixture amount of drug weighed

X = 15mg (amt of drug ordered) x 960mg (total mixture) 120mg (amt of drug weighed)

X = ?

240 120

Not Quite…Try Again!

Congratulations!From the 960 mg pile of mixture we will weigh out 120 mg.In that 120 mg will be the originally ordered 15mg of Augmentin. We can then mix it with the cherry syrup and the compound will be finished. The 840 mg of mixture left over may be discarded.

Now all that’s left is to label

it and dispense it to the waiting patient.