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Chapter 4 Calculation of Oral Medications ─ Solid and Liquids

Chapter 4 Calculation of Oral Medications ─ Solid and Liquids. Dosage Calculations. D = desired dose or order H = on hand or have S = supply. Four Methods of Dosage Calculation. Proportion expressed as two fractions Proportion expressed as two ratios Formula method Dimensional analysis.

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Chapter 4 Calculation of Oral Medications ─ Solid and Liquids

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  1. Chapter 4 Calculation of OralMedications─Solid and Liquids

  2. Dosage Calculations • D = desired dose or order • H = on hand or have • S = supply

  3. Four Methods of Dosage Calculation • Proportion expressed as two fractions • Proportion expressed as two ratios • Formula method • Dimensional analysis

  4. Proportion Expressed as Two Fractions • Supply = x Have Desire

  5. Proportion Expressed as Two Ratios • Supply : Have :: x : Desire

  6. Formula Method • Desire × Supply = x Have

  7. Dimensional Analysis • 1,000 mcg = 1 mg = 1,000 mcg or 1 mg 1 mg 1,000 mcg

  8. 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.

  9. Important to Remember • Before solving problems, check to be certain that the order and supply are in the same weight measure. • If not in the same weight measure, you must convert one or the other to its equivalent.

  10. Question The client is to receive acetaminophen 975 mg po every 6 hours prn for an earache. You have 325mg tablets available. How many tablets would the nurse administer? A. 2 tablets B. 3 tablets C. 4 tablets D. 5 tablets

  11. Answer B. 3 tablets • “Desire/Have × Supply = x” is the formula method. “Supply : Have :: x : Desire” is the proportion expressed as two ratios method. “Supply/Have = x/Desire” is the proportion expressed as two fractions 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 ratios method. “Tablet/325 mg = 3 tablets/975 mg” is the proportion expressed as two fractions method.

  12. Answer (continued) • “ Desired unit is 975mg”. You have 325mg tablets. X tab = 1 tab/325mg x 975mg/1. Using dimensional analysis cancel like units on right side of equation. The remaining unit should be what is desired and match the unit on the left side.

  13. Question The patient/client is to receive Mycostatin oral suspension 200,000 units po twice a day. The available Mycostatin oral suspension is 100,000 units per milliliter. How many milliliters of medication would the nurse administer? A. 1 mL B. 2 mL C. 3 mL D. 4 mL

  14. Answer • B. 2 mL • /;Desire/Have × Supply = x” is the formula method. “Supply : Have :: x : Desire” is the proportion expressed as two ratios method. “Supply/Have = x/Desire” is the proportion expressed as two fractions method. • “200,000 units/100,000 units × Milliliters = 2 mL” is the formula method. “Milliliters : 100,000 units :: 2 mL : 200,000 units” is the proportion expressed as two ratios method. “Milliliters/100,000 units = 2 mL/200,000 units” is the proportion expressed as two fractions method.

  15. Answer (continued) • “ Desired unit is 200,000 units ”. You have 100,000 units per milliliter. X milliliters = 1 mL/100,000 x 200,000/1. Using dimensional analysis cancel like units on right side of equation. The remaining unit should be what is desired and match the unit on the left side.

  16. Proficiency With Drug Calculations • Practice = Success

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