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Math for Medications Some terms youll see: Desired Dose Available Dose Ratio & Proportion Cross Product

Math for Medications The purpose of this class is for the learner to be able to calculate drug dosages of tablets and liquids. You will calculate the drug dosages using the formula or ratio & proportion method.

Math for Medications- the Formula Method for Tablets Desired doseX Vehicle = ATA Available dose ddxv = ATA ad(amount to administer)

Problem The doctor ordered Benadryl 75 mg. The drug label reads Benadryl 0.025 grams. How many tablets are needed? Read the problem and identify what youve been given.

Problem dd = 75 mg ad= 0.025 grams v = 1 tab Have both dd & ad in the same unit of measure 0.025 g = 25 mg. ad = 25 mg

Problem Put the numbers into the formula: 75 mgx1 tab =3 tabs 25 mg

Math for Medications- The Ratio & Proportion Method for Tablets We will use the same problem but will cross multiply.

Problem The doctor ordered Benadryl 75 mg. The drug label reads Benadryl 0.025 grams. How many tablets are needed? Read the problem and identify what youve been given.

Problem The known ratio: 25 mg 1 tablet The unknown ratio: 75 mg N tablets

Problem Write the proportion : 25 mg x 75 mg 1 tablet N tablets

Problem Cross Multiply: 25 mg x 75 mg 1 tablet N tablets 25mg X N tab = 1 X 75 mg

Problem Solve for N by dividing both sides of the equation by 25: 25 N=7525 or N = 3

Problem Substitute 3 for N in the original proportion and your answer is : You would administer 3 tablets to give a dosage of 75 mg.

Math for Medications for Liquids Calculate drug dosages using the formula method or ratio & proportion method for liquids.

Problem The doctor has ordered Gentamycin Sulphate 25 mg. The label reads Gentamycin Sulphate 40 mg/mL. How much Gentamycin will you administer?

Problem - Using the Formula Method Identify: dd = 25 mg ad = 40 mg v = 1 mL Put the numbers in the formula: 25x 1 mL= 0.625 mL 40

Problem Round off to the nearest decimal place: 25x 1 mL= 0.625 mL or 0.6 mL 40

Problem- Using the Ratio & Proportion method Cross product ( Cross Multiply) : The know ratio:40 mg 1 mL The unknown ratio:25 mg N mL

Problem Proportion:40 mg =25mg 1 mLN mL Cross Multiply: 40 x N = 1 x 25

Problem Solve for N: 40N=25 4040 N =0.625 Round off: N = 0.6 mL

Substitute for N in the original proportion: Proportion:40 mg =25mg 1 mL0.6 mL

Math for Medications Another way to calculate

Math for Medications The Math Chart Lets look at another way to calculate

Math for Medications The Math Chart When we are calculating drug dosages of tablets and liquids we always have 2 pieces of information. 1) What the label reads 2) What has the doctor ordered

Math for Medications The Math Chart The first step that we do when we use the Math Chart is to draw the chart which simply looks like this:

Math for Medications The Math Chart The second step in using the Math Chart is to label the chart. An important thing to remember when labelling the chart is to make sure that the top sections are the same and the bottom sections are the same.MgTablets

Math for Medications The Math Chart Once we have our chart filled in, all we do is MULTIPLY ON THE DIAGONAL AND DIVIDE BY WHATS LEFT Ex: Mg 30 45Mg Tablets 1Tablets Lets do our calculations: 45 X 1 ÷ 30 = 1.5 tablets

Math for Medications The Math Chart Lets look at the first example

Math for Medications The Math Chart The doctor ordered Benadryl 75 mg. The drug label reads Benadryl 0.025 grams. How many tablets are needed? **The first thing we have to do is to look at what information we have. 1)What the label reads – 0.025g for 1 tablet 2)What the doctor ordered – 75mg

Math for Medications The Math Chart ***Before me make our chart we have to make sure both units are the same. In this question, we have 0.025 g & 75 mg Lets change 0.025g to mg by multiplying by 1000 Now both units are the same 25mg and 75mg and we can make our chart

Math for Medications The Math Chart Step 1 - Make the chart and label it Step 2 – Fill in the information that we haveMg 25 75 1 Tablets Step 3 – Do the calculations MULTIPLY ON THE DIAGONAL AND DIVIDE BY WHATS LEFT 75 X 1 ÷ 25 = 3 tablets

Math for Medications The Math Chart Lets try the next example: The doctor has ordered Gentamycin Sulphate 25 mg. The label reads Gentamycin Sulphate 40 mg/mL. How much Gentamycin will you administer?

Math for Medications The Math Chart **The first thing we have to do is to look at what information we have. 1)What the label reads – 40mg for 1 mL 2)What the doctor ordered 25mg

Math for Medications The Math Chart Step 1 - Make the chart and label it Step 2 - Fill in the information we have Mg 4025 1 mL Step 3 – Do our calculations 25 x 1 ÷ 40 = 0.625 mL

Rules to Remember Example: 0.66mg = 0.7 mg 1.Put 0 to the left of the decimal if there is no whole number. 2.Adults: round of drug doses to the nearest 1/10 or 0.1. 3.Pediatrics: Round off drug doses to the nearest 1/100 or 0.01

Rules to Remember Do not round off until your final answer: For example:100 mg x 15 mL 80 mg 10=1.25 x 15 mL = 18.75 mL 8 Not 1.3 x 15 mL which would =19.5mL

References AOM coursepack

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