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Math for Medications

Math for Medications. Some terms you’ll 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.

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Math for Medications

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  1. Math for Medications Some terms you’ll see: Desired Dose Available Dose Ratio & Proportion Cross Product

  2. 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.

  3. Math for Medications- the Formula Method for Tablets Desired dose X Vehicle = ATA Available dose • dd x v = ATA ad (amount to administer)

  4. 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 you’ve been given.

  5. 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

  6. Problem • Put the numbers into the formula: 75 mg x 1 tab = 3 tabs 25 mg

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

  8. 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 you’ve been given.

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

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

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

  12. Problem • Solve for N by dividing both sides of the equation by 25: • 25 N = 75 25 25 or N = 3

  13. 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.

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

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

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

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

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

  19. Problem • Proportion: 40 mg = 25mg 1 mL N mL • Cross Multiply: 40 x N = 1 x 25

  20. Problem • Solve for N: 40N = 25 40 40 N = 0.625 N = 0.625 Round off: N = 0.6 mL

  21. Substitute for N in the original proportion: • Proportion: 40 mg = 25mg 1 mL 0.6 mL

  22. Math for Medications Another way to calculate

  23. Math for Medications The “Math Chart” • Lets look at another way to calculate

  24. Math for MedicationsThe “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

  25. Math for MedicationsThe “Math Chart” • The first step that we do when we use the Math Chart is to draw the chart which simply looks like this:

  26. Math for MedicationsThe “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. Mg Mg Tablets Tablets

  27. Math for MedicationsThe “Math Chart” • Once we have our chart filled in, all we do is MULTIPLY ON THE DIAGONAL AND DIVIDE BY WHAT’S LEFT Ex: Mg 30 45 Mg Tablets 1 Tablets Lets do our calculations: 45 X 1 ÷ 30 = 1.5 tablets

  28. Math for MedicationsThe “Math Chart” • Lets look at the first example

  29. Math for MedicationsThe “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. • What the label reads – 0.025g for 1 tablet • What the doctor ordered – 75mg

  30. Math for MedicationsThe “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

  31. Math for MedicationsThe “Math Chart” • Step 1 - Make the chart and label it • Step 2 – Fill in the information that we have Mg Mg 25 75 1 Tablets Tablets • Step 3 – Do the calculations MULTIPLY ON THE DIAGONAL AND DIVIDE BY WHAT’S LEFT 75 X 1 ÷ 25 = 3 tablets

  32. Math for MedicationsThe “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?

  33. Math for MedicationsThe “Math Chart” **The first thing we have to do is to look at what information we have. • What the label reads – 40mg for 1 mL • What the doctor ordered 25mg

  34. Math for MedicationsThe “Math Chart” • Step 1 - Make the chart and label it • Step 2 - Fill in the information we have Mg Mg 40 25 1 mLmL • Step 3 – Do our calculations • 25 x 1 ÷ 40 = 0.625 mL

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

  36. 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

  37. References • AOM coursepack

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