DOSAGE CALCULATIONS
Desired
What is the desired
(ordered amount)?
DOSAGE CALCULATIONS
Have
What do you have
(amount on hand)?
DOSAGE CALCULATIONS
Vehicle
How is the dosage measured
(quantity)?
DOSAGE CALCULATIONS
D
H
V
Desired over Have times Vehicle
DOSAGE CALCULATIONS
The order reads
Lasix 20 mg po
You have
Lasix 20 mg tablets
How many tablets will you give?
Desired over Have times Vehicle
DOSAGE CALCULATIONS
20 mg
20 mg
1 tablet
Desired over Have times Vehicle
DOSAGE CALCULATIONS
20 mg
20 mg
1 tablet
The labels of Desired and Have MUST match
DOSAGE CALCULATIONS
20 mg
20 mg
1 tablet
If the labels match, then they cancel each other out
DOSAGE CALCULATIONS
20
20
1 tablet
Reduce the fraction if possible
DOSAGE CALCULATIONS
1
1
1 tablet
Do the multiplication
DOSAGE CALCULATIONS
1 1 tablet = 1 tablet
Calculate the Dosage
DOSAGE CALCULATIONS
Give 1 tablet
Amount to Give
DOSAGE CALCULATIONS
The order reads
Lasix 30 mg po
You have
Lasix 20 mg tablets
How many tablets will you give?
Desired over Have times Vehicle
DOSAGE CALCULATIONS
30 mg
20 mg
1 tablet
Desired over Have times Vehicle
DOSAGE CALCULATIONS
30 mg
20 mg
1 tablet
The labels of Desired and Have MUST match
DOSAGE CALCULATIONS
30 mg
20 mg
1 tablet
If the labels match, then they cancel each other out
DOSAGE CALCULATIONS
30
20
1 tablet
Reduce the fraction if possible
DOSAGE CALCULATIONS
3
2
1 tablet
Do the multiplication
DOSAGE CALCULATIONS
1
1
2
1 tablet
Calculate the Dosage
DOSAGE CALCULATIONS
Give 1
1
2
Tablets
Amount to Give
DOSAGE CALCULATIONS
The order reads
Dilantin Suspension 200 mg po
You have
Dilantin Suspension 125 mg / 5 mL
How many mL will you give?
Desired over Have times Vehicle
DOSAGE CALCULATIONS
200 mg
125 mg
5 mL
Desired over Have times Vehicle
DOSAGE CALCULATIONS
200 mg
125 mg
5 mL
The labels of Desired and Have MUST match
DOSAGE CALCULATIONS
200 mg
125 mg
5 mL
If the labels match, then they cancel each other out
DOSAGE CALCULATIONS
200
125
5 mL
Reduce the fraction if possible
DOSAGE CALCULATIONS
8
5
5 mL
Do the multiplication
DOSAGE CALCULATIONS
8
1
1 mL
Calculate the Dosage
DOSAGE CALCULATIONS
Give 8 mL
Amount to Give
DOSAGE CALCULATIONS
The order reads
Morphine Sulfate gr ¼ sc
You have
Morphine Sulfate 10 mg / 1 mL
How many mL will you give?
Does the dosage need to be converted?
DOSAGE CALCULATIONS
The order reads
Morphine Sulfate gr ¼ sc
You have
Morphine Sulfate 10 mg / 1 mL
How many mL will you give?
Caution: The labels MUST match!
CONVERSIONS
Converting Between the Systems
Weight
60 mg = gr i
The Metric System and the Apothecary System
CONVERSIONS
Setting Up the Proportion
Step 1: What DO you know?
60 mg = 1 gr
This is the first part of your proportion
60 mg : 1 gr :: 45 mg : x gr
CONVERSIONS
Setting Up the Proportion
Step 1: What DO you know?
60 mg = 1 gr
This is the first part of your proportion
60 mg : 1 gr :: 45 mg : x gr
CONVERSIONS
Setting Up the Proportion
Step 2: What do you WANT to know?
x mg = gr ¼
This is the second part of your proportion
60 mg : 1 gr :: x mg : ¼ gr
CONVERSIONS
Checking the Proportion
Step 3: Are the labels in the same order?
60 mg : 1 gr :: x mg : ¼ gr
mg : gr
mg : gr
Caution: Changing the order of the labels
will yield the WRONG ANSWER
CONVERSIONS
Step 4: Solve the proportion
60 mg : 1 gr :: x mg : ¼ gr
x = 60 ¼
x=
60
4
x = 15 mg
Caution: Don’t forget to LABEL your answer
CONVERSIONS
Step 4: Solve the proportion
60 mg : 1 gr :: x mg : ¼ gr
x = 60 ¼
x=
60
4
x = 15 mg
Caution: Do you have the RIGHT label?
DOSAGE CALCULATIONS
The order reads
Morphine Sulfate gr ¼ sc
You now know
gr ¼ = 15 mg
You can convert this order to
Morphine Sulfate 15 mg sc
Look back at the order
DOSAGE CALCULATIONS
The order is
Morphine Sulfate 15 mg sc
You have
Morphine Sulfate 10 mg / 1 mL
How many mL will you give?
Now use Desired over Have times Vehicle
DOSAGE CALCULATIONS
15 mg
10 mg
1 mL
Desired over Have times Vehicle
DOSAGE CALCULATIONS
15 mg
10 mg
1 mL
The labels of Desired and Have MUST match
DOSAGE CALCULATIONS
15 mg
10 mg
1 mL
If the labels match, then they cancel each other out
DOSAGE CALCULATIONS
15
10
1 mL
Reduce the fraction if possible
DOSAGE CALCULATIONS
3
2
= 1.5
Remember: The metric system uses decimals
DOSAGE CALCULATIONS
1.5
1 mL
Do the multiplication and calculate the dosage
DOSAGE CALCULATIONS
Give 1.5 mL
Amount to Give
DOSAGE CALCULATIONS
The order is
Morphine Sulfate 15 mg sc
You have
Morphine Sulfate 10 mg / 1 mL
You will give
1.5 mL Morphine Sulfate
Look back to the original order
DOSAGE CALCULATIONS
The order is
Morphine Sulfate 15 mg sc
You have
Morphine Sulfate 10 mg / 1 mL
How many mL will you give?
You can also use the Proportion Method
DOSAGE CALCULATIONS
Using the Proportion Method
Step 1: What do you Have (Label)?
Morphine Sulfate 10 mg / 1 mL
This is the first part of your proportion
10 mg : 1 mL :: 45 mg : x gr
DOSAGE CALCULATIONS
Using the Proportion Method
Step 2: What do you Desire (Order)?
Morphine Sulfate 15 mg
This is the second part of your proportion
10 mg : 1 mL :: 15 mg : x mL
DOSAGE CALCULATIONS
Using the Proportion Method
Step 3: Are the labels in the same order?
10 mg : 1 mL :: 15 mg : x mL
mg : mL
mg : mL
Caution: Changing the order of the labels
will yield the WRONG ANSWER
DOSAGE CALCULATIONS
Step 4: Solve the proportion
10 mg : 1 mL :: 15 mg : x mL
15 = 10x
15 = x
10
x = 1.5 mL
Caution: Don’t forget to LABEL your answer
DOSAGE CALCULATIONS
Step 4: Solve the proportion
10 mg : 1 mL :: 15 mg : x mL
15 = 10x
15 = x
10
x = 1.5 mL
Caution: Do you have the RIGHT label?
DOSAGE CALCULATIONS
The order is
Morphine Sulfate 15 mg sc
You have
Morphine Sulfate 10 mg / 1 mL
You will give
1.5 mL Morphine Sulfate
Look back to the original order
DOSAGE CALCULATIONS
The order reads
Dilantin Suspension 400 mg po
You have
Dilantin Suspension 125 mg / 5 mL
How many mL will you give?
Calculate this dose using the D/H * V Method
DOSAGE CALCULATIONS
The order reads
Dilantin Suspension 400 mg po
You have
Dilantin Suspension 125 mg / 5 mL
How many mL will you give?
Calculate this dose using the Proportion Method
DOSAGE CALCULATIONS
Desired over Have times Vehicle
– or –
Set up a Proportion
It’s really YOUR Choice