1. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 6 Calculation of Oral Medications ─ Solid and Liquids

2. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Dosage Calculations D = Desired dose or order H = On hand or have S = Supply

3. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Three Methods of Dosage Calculation Proportion expressed as two fractions Proportion expressed as two ratios Formula method

4. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Proportion Expressed as Two Fractions SUPPLY = X HAVE DESIRE

5. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Proportion Expressed as Two Ratios SUPPLY : HAVE :: X : DESIRE

6. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Formula Method DESIRE × SUPPLY = X HAVE

7. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Clearing Decimals When the numerator and denominator in Desire/Have are decimals, add zeros to make the number of decimal places the same Then drop the decimal points Operation replaces long division

8. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Important to Remember Before solving problems, check to be certain the order and supply are in the measure If not in same measure, must convert one or the other to its equivalent

9. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question The client is to receive acetaminophen 975 mg po every 6 hours prn for an earache. How many tablets would the nurse administer? A.2 B.3 C.4 D.5

10. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. 3 Desire/Have × Supply = X is the formula method. Supply : Have :: X : Desire is the proportion expressed as two ratio method. Supply/Have = X/Desire is the proportion expressed as two fraction method 975 mg/325 mg × tablet = 3 tablets is the formula method. tablet : 325 mg :: 3 tablets : 975 mg is the proportion expressed as two ratio method. tablet/325 mg = 3 tablets/975 mg is the proportion expressed as two fraction method

11. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question The client is to receive Mycostatin oral suspension 200,000 units po twice a day. The available Mycostatin oral suspension is 100,000 units per mL. How many milliliters of medication would the nurse administer? A.1 B.2 C.3 D.4

12. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. 2 –Desire/Have × Supply = X is the formula method. Supply : Have :: X : Desire is the proportion expressed as two ratio method. Supply/Have = X/Desire is the proportion expressed as two fraction method –200,000 units/100,000 units × milliliter = 2 milliliters is the formula method. milliliter : 100,000 units :: 2 milliliters : 200,000 units is the proportion expressed as two ratio method. milliliter/100,000 units = 2 milliliters/200,000 units is the proportion expressed as two fraction method

13. Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Proficiency With Drug Calculations Practice = Success