Math for the Pharmacy Technician: Concepts and Calculations

1. Math for the Pharmacy Technician: Concepts and Calculations Egler • Booth Chapter 7: Oral Medications and Parenteral Dosages

2. Oral Medications and Parenteral Dosages

3. Learning Objectives • Distinguish between different types of oral medications. • Recognize the types of solid oral medications that may not be altered by crushing or opening them. • Calculate the amount of a parenteral medication to administer. When you have successfully completed Chapter 7, you will have mastered skills to be able to:

4. Learning Objectives (con’t) • Select the appropriate syringe. • Correctly reconstitute powdered medications. • Calculate the amount of reconstituted medications to administer. • Accurately calculate doses of inhalant, rectal, and transdermal medications. • Identify errors that occur in calculating and preparing parenteral doses. • Calculate estimated days supply.

5. Introduction • You will learn to apply the simple calculation methods learned in Chapter 6 to oral dosages, including solids and liquids. • Follow the method of calculation that you have chosen by following the color coded examples. Remember that excellence is a must with dosage calculations.

6. Tablets • Caplets • Capsules Tablets and Capsules Solid oral medications come in several forms:

7. Tablets Most common form of solid oral medications • Combines with inactive ingredients • Forms a solid disk or cylinder • to be swallowed • sublingual • buccal • chewable • dissolve in water

8. Caplets • Oval-shaped • Special coating -- easier to swallow Caplet

9. Capsules • Oval-shaped gelatin shells • Contain medication in powder or granule form • The shell is usually two pieces that fit together • The shell can be separated to remove the medication when the patient cannot swallow a pill

10. Gelcaps • Usually a liquid medication in a gelatin shell • Not designed to be opened

11. Scored Tablets • Scoring allows the tablet to be divided when smaller doses are ordered • Most often, scored tablets divide into halves • Some divide into thirds or quarters • Medication is evenly distributed throughout the tablet

12. Calculating Dosages for Tablets and Capsules • Always question and/or verify when your calculation indicates to give a portion of a tablet when the tablet is not scored. • Question and recheck any calculation that indicates that you should dispense more than three tablets or capsules.

13. Calculating Dosages for Tablets and Capsules(con’t) Follow these steps when determining the amount of medication to be dispensed to a patient: • If necessary, convert the dosage ordered (O) to the desired dose (D) that has the same unit of measurement as the dose on hand (H). • Calculate the amount to dispense by the method of your choice.

14. Calculating Dosages for Tablets and Capsules(con’t) Follow these steps when determining the amount of medication to be dispensed to a patient: 3.Apply critical thinking skills to determine whether the amount you have calculated is reasonable. Recheck your calculation if necessary.

15. Review and Practice The order is to give the patient 15 mg codeine PO now. You have 30 mg tablets available. Calculate the correct amount of medication to give using one of the following methods. • Fraction Proportion • Ratio Proportion • Dimensional Analysis • Formula Method

16. Fraction Proportion Method Calculating the Amount to Dispense by Fraction Proportion: 1. Set up the proportion as follows: dosage unitamount to dispense dose on handdesired dose 2. Cancel units. 3. Cross multiply, then solve for the unknown value.

17. Ratio Proportion Method Calculating the Amount to Dispense by Ratio Proportion: • The proportion will be set up as follows: dosage unit : dose on hand :: amount to dispense : desired dose Or Q : H :: A : D 2. Cancel units. 3. Multiply the means and extremes then solve for the missing value.

18. Dimensional Analysis Method Calculating the Amount to Dispense by Dimensional Analysis: With dimensional analysis you will not need to calculate the desired dose and amount to dispense separately. You will place your unknown (amount to dispense) on one side of the equation then multiply a series of factors on the right side of the equation. Canceling units will help you determine the equation has been set up correctly.

19. Dimensional Analysis Method (con’t) Calculating the Amount to Dispense by Dimensional Analysis (con’t): • Determine the units of measure for the answer and place it as the unknown on one side of the equation. • On the right side of the equation, write a conversion factor with the units of measurement for the desired dose on top and the unit of measurement for the dose on hand.

20. Dimensional Analysis Method (con’t) Calculating the Amount to Dispense by Dimensional Analysis (con’t): • Multiply the conversion factor by a second factor: the dosage unit over the dose on hand. • Multiply by a third factor: dose ordered over the number one. • Cancel units on the right side of the equation. The remaining unit of measure on the right side of the equation should match the unknown unit of measure on the left side of the equation. • Solve the equation.

21. Formula Method Calculating Amount to Dispense Using the Formula Method: 1. Determine the desired dose. Determine the dose on hand (H) and dosage unit (Q) • 2. Fill the formula • D for the desired dose • H for the dose on hand • Q for the dosage unit in the formula • A for the unknown or the amount to dispense

22. Formula Method (con’t) Calculating Amount to Dispense Using the Formula Method (con’t): 3. Cancel the units. 4. Solve for the unknown.

23. Review and Practice The order is to give the patient 15 mg codeine PO now. You have 30 mg tablets available. Calculate the correct amount of medication to give using one of the following methods. • Fraction Proportion • Ratio Proportion • Dimensional Analysis • Formula Method Answer: ½ tablet

24. Crushing Tablets or Opening Capsules Uses: • Patients who have difficulty swallowing pills • Patients who have tube feedings • nasogastric tubes • gastrostomy tubes • jejunostomy tubes May need physician order first • Check the policy

25. Crushing Tablets or Opening Capsules(con’t) Mixing • Crush certain tablets. • Open certain capsules. • Mix with soft foods or liquids. • Check for interactions between medication and the food or fluid. • Example - Tetracycline is inactivated by milk and should not be given with antacids or vitamin and mineral supplements.

26. Crushing Tablets or Opening Capsules (con’t) Tube feedings • Must first dissolve the crushed tablet or opened capsule in a small amount of warm water. • If medication cannot be crushed, see if an alternative form of the medication exists and ask the physician to order it that way.

27. Some Common Food and Drug Interactions

28. Some Common Food and Drug Interactions(con’t)

29. Some Common Food and Drug Interactions(con’t)

30. Some Common Food and Drug Interactions(con’t)

31. Crushing Tablets or Opening Capsules To prevent an incorrect dose of medication, do not crush or otherwise alter any of the following: • Enteric-coated tablets • Sustained-release forms of medication • Any tablet with a hard shell or coating • Tablets for sublingual or buccal use • Capsules with seals that prevent separating the two parts

32. Enteric-coated Tablets • Have a coating that dissolves only in an alkaline environment such as the small intestine • Deliver medication that would be destroyed by the stomach acid or that could injure the stomach lining

33. Enteric-coated Tablets (con’t) • Often look like candies that have a soft center and a hard shell • Must neverbe crushed, broken, or chewed • Must be swallowed with their coating intact

34. Sustained-Release Medications • Allows the drug to be released slowly into the bloodstream over a period of several hours. • If the medication is scored, it may be broken at the scored line. • Do not crush or dissolve. • This would allow too much medication to be absorbed at one time.

35. Spansules • These contain granules of medication with different coatings that delay release of some of the medication. • You may open spansules and gently mix the granules in soft food, but do not crush or dissolve the granules.

36. Medications That Must Not Be Crushed or Dissolved • Names that indicate sustained-release medications: -Bid LA Tempule -Dur CR Chronotab Plateau Cap XL Repetab Span Sequel Tembid SA Spansule SR Extentab

37. Medications That Must NotBe Crushed or Dissolved (con’t) • Names that indicate enteric-coated medications: EC Enseal

38. Reconstituting Liquid Medications Reconstituting Liquid Medications: • Use only the liquid specified on the drug label. • Use the exact amount of liquid specified on the drug label. • Check the label to determine whether the medication should be shaken before dispensing.

39. Reconstituting Liquid Medications(con’t) Reconstituting Liquid Medications: • Check the label to determine whether the reconstituted medication must be refrigerated. • Write on the label • The date and time you reconstituted the medication. • Your initials. • Strength of reconstitution.

40. Reconstituting Liquid Medications(con’t) Reconstituting Liquid Medications: • Check the label to determine how long the reconstituted medication may be stored. • Discard any medication left after this time period has passed.

41. Reconstituting Liquid Medications(con’t) Reconstituting Liquid Medications: • When medication can be reconstituted in different strengths, select the strength that will allow the desired dose in the smallest volume.

42. Reconstituting Liquid Medications(con’t) Reconstituting Liquid Medications: • Read the order carefully when calculating the amount to dispense. • The physician usually orders the dose in units of drug, not volume of liquid. • Calculate the volume needed to dispense the desired dose.

43. To calculate the volume of liquid oral medication to Dispense, use the same methods that you use for solid oral medications: • fraction proportions • ratio proportions • formula • dimensional analysis Calculating the Volume of Liquid Oral Medication

44. Calculating the Volume of Liquid Oral Medication (con’t) Find the amount to Dispense. • Ordered: Ventolin 5 mg PO now • On hand: Ventolin syrup 2 mg per 5 mL Use the calculation method of choice.

45. Fraction Proportion Method Calculating the Amount to Dispense by Fraction Proportion: 1. Set up the proportion as follows: dosage unitamount to Dispense dose on handdesired dose 2. Cancel units. 3. Cross multiply, then solve for the unknown value.

46. Ratio Proportion Method Calculating the Amount to Dispense by Ratio Proportion: • The proportion will be set up as follows: dosage unit : dose on hand :: amount to Dispense : desired dose Or Q : H :: A : D 2. Cancel units. 3. Multiply the means and extremes then solve for the missing value.

47. Dimensional Analysis Method Calculating the Amount to Dispense by Dimensional Analysis: With dimensional analysis you will not need to calculate the desired dose and amount to dispense separately. You will place your unknown (amount to dispense) on one side of the equation then multiply a series of factors on the right side of the equation. Canceling units will help you determine the equation has been set up correctly.

48. Dimensional Analysis Method Calculating the Amount to Dispense by Dimensional Analysis (con’t): • Determine the units of measure for the answer and place it as the unknown on one side of the equation. • On the right side of the equation, write a conversion factor with the units of measurement for the desired dose on top and the unit of measurement for the dose on hand. • Multiply the conversion factor by a second factor: the dosage unit over the dose on hand.

49. Dimensional Analysis Method Calculating the Amount to Dispense by Dimensional Analysis (con’t): 4. Multiply by a third factor: dose ordered over the number one. 5. Cancel units on the right side of the equation. The remaining unit of measure on the right side of the equation should match the unknown unit of measure on the left side of the equation. 6. Solve the equation.

50. Formula Method Calculating Amount to Dispense Using the Formula Method: 1. Determine the desired dose. Determine the dose on hand (H) and dosage unit (Q) • 2. Fill the formula • D for the desired dose • H for the dose on hand • Q for the dosage unit in the formula • A for the unknown or the amount to dispense