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Chapter 9

Chapter 9. Calculating Doses of Nonparenteral Medications. Nonparenteral Medications. Three methods used ratio and proportion formula method dimensional analysis Two parts dose ordered (DO) dosage available (DA). Calculating Solid Doses.

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Chapter 9

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  1. Chapter 9 Calculating Doses of Nonparenteral Medications

  2. Nonparenteral Medications

  3. Three methods used ratio and proportion formula method dimensional analysis Two parts dose ordered (DO) dosage available (DA) Calculating Solid Doses

  4. Identify available unit to be used for desired dose tablets, capsules, mL, ounces Ensure all units are alike conversions must be done prior to calculation of the dose Verify dose calculation with medication order Calculating Doses

  5. Ratio and Proportion Terminology

  6. First set of comparisons dosage available (DA) located right side Other side of equation dose ordered (DO) located left side Dosage available (DA) : Dosage form = Dose ordered (DO) : Dose to be given Always perform dose calculations in writing Proportional Method

  7. Ordered: Glucophage 850 mg qd po with meal Dosage available: Glucophage 850 mg tablets Are the units in the same measurement? Proportional Method

  8. Proportional Method • Ordered: Glucophage 850 mg qd po with meall • Dosage available: Glucophage 850 mg tablets • Are the units in the same measurement? Yes

  9. Ordered: Glucophage 850 mg qd po with meal Dosage available: Glucophage 850 mg tablets Are the units in the same measurement? Yes 850 mg (DA) : 1 tablet (form) :: 850 mg (DO) : # tablet(s) (dose to be given) Proportional Method

  10. Proportional Method • 850 mg (DA) : 1 tablet (form) :: 850 mg (DO) :# tablet(s) (dose to be given) • x stands for dose to be given • 850 is to x as 850 is to 1 • 850 : 1 :: 850 : x • 850x = 850 • x = 1 • Answer: one 850 mg tablet daily

  11. Proportional Method • Ordered: phenobarbital gr 1/2 po tid • Dosage available (DA): phenobarbital gr 1/4 tablet • Are the units in the same measurement?

  12. Proportional Method • Ordered: phenobarbital gr 1/2 po tid • Dosage available (DA): phenobarbital gr 1/4 tablet • Are the units in the same measurement? Yes

  13. Ordered: phenobarbital gr 1/2 po tid Dosage available (DA): phenobarbital gr 1/4 tablet Are the units in the same measurement? Yes gr 1/4 (DA) : 1 tablet (dosage form) :: gr 1/2 (DO) : x # tablet(s) (dose to be given) Proportional Method

  14. gr 1/4 (DA) : 1 tablet (dosage form) :: gr 1/2 (DO) : x # tablet(s) (dose to be given) 1/4 : 1 :: 1/2 : x 1/4 is to x as 1/2 is to 1 1/4 x = 1/2 Invert fraction before multiplying x = 1/2 x 4/1 x = 2 Desired dose is two gr 1/4 tablets three times daily Proportional Method

  15. Ordered: phenobarbital gr iii po hs Dosage available (DA): phenobarbital 100 mg scored tablet Are the units in the same measurement? Proportional Method

  16. Ordered: phenobarbital gr iii po hs Dosage available (DA): phenobarbital 100 mg scored tablet Are the units in the same measurement? No Proportional Method

  17. Ordered: phenobarbital gr iii po hs Dosage available (DA): phenobarbital 100 mg scored tablet Are the units in the same measurement? No What is the equivalency? Proportional Method

  18. Ordered: phenobarbital gr iii po hs Dosage available (DA): phenobarbital 100 mg scored tablet Are the units in the same measurement? No What is the equivalency? 60 mg = 1 grain (gr i) Proportional Method

  19. Proportional Method Conversion • 60 mg = 1 grain (gr i) • 60 mg : 1 gr :: 100 mg : x • 100 mg = 1½ grains gr iss • 100 mg : gr iss :: x mg : gr iii • 100 is to 1½ as x is to 3 • 1½ x = 300 • Change 1½ to 3/2 • 100 mg : 3/2 = x : 3 • 3/2x = 300 • x = 300 x 2/3 • x = 200 mg

  20. Proportional Method • 100 mg (DA) : 1 tablet (form) :: 200 mg (DO) : x (dose to be given) • 100 : 1 :: 200 : x • 100 is to x as 200 is to 1 • 100x = 200 • x = 2 • Desired dose is two 100 mg tablets every day at bedtime

  21. Proportional Method • Ordered: oxybutynin HCl 10 mg po bid • Available: 5 mg scored tablets • Are the units in the same measurements?

  22. Proportional Method • Ordered: oxybutynin HCl 10 mg po bid • Available: 5 mg scored tablets • Are the units in the same measurements? • Yes

  23. Proportional Method • Ordered: oxybutynin HCl 10 mg po bid • Available: 5 mg scored tablets • Are the units in the same measurements? • Yes • 5 mg (DA) : 1 tablet (form) :: 10 mg (DO) : # tablet(s) (dose to be given)

  24. Proportional Method • 5 mg (DA) : 1 tablet (form) :: 10 mg (DO) : # tablet(s) (dose to be given) • 5 is to 1 as 10 is to x • 5x = 10 • x = 2 • Desired dose is two 5 mg tablets, twice daily

  25. Formula Method • Dosage ordered (DO) / Dosage available (DA) x Quantity or Form (Qty) = Dose to be given • DO / DA x Qty = Dose to be given • Always perform dosage calculations in writing

  26. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements?

  27. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements? • Yes

  28. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements? • Yes • What is the desired dose?

  29. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements? • Yes • What is the desired dose? • 850 mg tablet daily

  30. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements? • Yes • What is the desired dose? • 850 mg tablet daily • DO (850 mg) / DA (850 mg) x Qty (1 tablet) = 1 tablet (dose to be given)

  31. Formula Method • Ordered: Glucophage 850 mg po qd with meal • Available: Glucophage 850 mg tablets • Are the units in the same measurements? • Yes • What is the desired dose? • 850 mg tablet daily • DO (850 mg) / DA (850 mg) x Qty (1 tablet) = 1 tablet (dose to be given) • Answer: One 850 mg tablet

  32. Formula Method • Ordered: phenobarbital gr iii po qd hs • Available: phenobarbital 100 mg scored tablets • Are the units in the same measurement?

  33. Formula Method • Ordered: phenobarbital gr iii po qd hs • Available: phenobarbital 100 mg scored tablets • Are the units in the same measurement? • No

  34. Formula Method • Ordered: phenobarbital gr iii po qd hs • Available: phenobarbital 100 mg scored tablets • Are the units in the same measurement? • No • What is the equivalency for conversion?

  35. Formula Method • Ordered: phenobarbital gr iii po qd hs • Available: phenobarbital 100 mg scored tablets • Are the units in the same measurement? • No • What is the equivalency for conversion? • gr I = 60 mg

  36. Formula Method Conversion • 60 mg = 1 grain (gr i) • 60 mg : 1 gr :: 100 mg : x • 100 mg = 1½ grains (gr iss) • 100 mg : gr iss :: x mg : gr iii • 100 is to 1½ as x is to 3 • 1½ x = 300 • Change 1½ to 3/2 • 100 mg : 3/2 = x : 3 • 3/2x = 300 • x = 300 x 2/3 • x = 200 mg

  37. Formula Method • 200 mg (DO) / 100 mg (DA) x 1 tablet (Qty) = 2 tablets (Dose to be given) • Answer: Two 100 mg tablets

  38. Formula Method • Ordered: oxybutynin HCl 10 mg po bid • Available: oxybutynin HCl 5 mg scored tablets • Are the units in the same measurement?

  39. Formula Method • Ordered: oxybutynin HCl 10 mg po bid • Available: oxybutynin HCl 5 mg scored tablets • Are the units in the same measurement? • Yes

  40. Formula Method • Ordered: oxybutynin HCl 10 mg po bid • Available: oxybutynin HCl 5 mg scored tablets • Are the units in the same measurement? • Yes • 10 mg (DO) / 5 mg (DA) x 1 tablet (Qty)

  41. Formula Method • Ordered: oxybutynin HCl 10 mg po bid • Available: oxybutynin HCl 5 mg scored tablets • Are the units in the same measurement? • Yes • 10 mg (DO) / 5 mg (DA) x 1 tablet (Qty) • Answer: Two 5 mg tablets

  42. Calculating Liquid Doses • Must convert to household system—patients more familiar with household than metric • Two numbers for drug dose calculation • amount of active ingredients (usually mg) • amount of liquid mixed with drug (usually mL) • mg/mL

  43. Reconstitution • Must reconstitute some medications from powder to liquid form prior to administering • Label gives total volume in bottle, medication strength Figure 9-1. Label for Zithromax.Courtesy of Pfizer Labs, New York.

  44. Reconstitution Different dosage strengths created with different amounts of water Always document strength, date, time of reconstitution on medication label, and initial

  45. Two Active Ingredients • Protuss • Each 5 mL (1 teaspoon) contains: • hydrocodone bitartrate 5 mg • potassium guaiacolsulfonate 300 mg • Remember: 5 mL = 1 tsp = 1 fluid dram (f )

  46. Liquid Medications • Ordered: Protuss f iss po prn • Available: Protuss, 5 mg hydrocodone bitartrate, and 300 mg potassium guaiacolsulfonate in each 5 mL. • Are the units in the same measurement?

  47. Liquid Medications • Ordered: Protuss f iss po prn • Available: Protuss, 5 mg hydrocodone bitartrate, and 300 mg potassium guaiacolsulfonate in each 5 mL. • Are the units in the same measurement?No

  48. Liquid Medications Conversion • 1 fluid dram (f ) = 1 teaspoon (tsp) = 5 mL • f (DA) : 5 ml (form) :: f iss (DO) : x mL (dose to be given) • 1 : 5 :: 1½ : x • 1 is to 5 as 1½ is to x • 5 x 3/2 = x • x = 7.5 mL • Desired dose is 7.5 mL = 1½ tsp

  49. Liquid Medications • Ordered: Augmentin 400 mg po q 12 hr • Available: Augmentin 400 mg/5 mL oral suspension • Are the units in the same measurement?

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