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Medication Calculations

Medication Calculations. Randall Stennett RN, MSN. Medication Calculations. Learning objectives You should be able to: calculate weight in Kilograms calculate Therapeutic dose calculate Concentration/Dilution calculate Rate of administration

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Medication Calculations

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  1. Medication Calculations Randall Stennett RN, MSN

  2. Medication Calculations • Learning objectives • You should be able to: • calculate weight in Kilograms • calculate Therapeutic dose • calculate Concentration/Dilution • calculate Rate of administration • Take the appropriate action based on your calculations

  3. To complete this presentation you will need: • Pencil • Paper • Calculator • Drug references

  4. References • Lefever-Kee, J, and Marshall, S.M., (2009), Clinical Calculations with Applications to General and Specialty Areas. (6th ed.) St.Louis: Elsevier. • Morris, D.G., (2006). Calculate with Confidence, (4th ed.) St. Louis: Mosby • Gahart, B. and Nazareno, A. (2009). Intravenous Medications (23rd ed.) St. Louis: Mosby • Lexi-Comp Online http://online.com/crlonline

  5. 1st order of business • This presentation is divided into 3 ‘sections’. • Each section will address 2-3 topics. • The content will be reviewed during the first three weeks of class.

  6. Week 1 Weight in kilograms/Therapeutic dose • Week 2 Concentration/Rate of Administration • Week 3 Taking appropriate action/ Putting it all together (Multifaceted problems)

  7. Medication errors account for at least 7,000 deaths in the United States each year. • Medication errors occur in nearly 1 of every 5 doses given to patients in the typical hospital.* *Barker KN, Flynn EA, Pepper GA, PhD, Bates DW, Mikeal RL. Medication errors observed in 36 health care facilities. Arch Intern Med 2002;162:1897-1903.

  8. Calculation Quizzes ►There will be 4 quizzes throughout the semester (each is comprehensive) ► 25 questions on each quiz ► 1 hour for each quiz ► Each question = 1 point ► Point total for all quizzes will become your 9th theory exam and will be factored into your final theory grade

  9. ►I am available for any help you may need. ►I will be happy to work with you one-on-one, or in small groups. ►In the past, small groups, at the end of lecture periods, has worked well. ►Randall Stennett • Office 122 • Phone 797-0955 ext 246 • Email through Scholar 360 • I will attempt to return email within 1-2 days

  10. Review • There are 3 ways to work your calculations • Basic Formula • Ratio and Proportion and • Fractional Equation • You, most likely have your preferred method , use what works for you! • Here is a quick review of the methods.

  11. Review • Basic Formula (BF) Dx V = X (amount to give) H D: desired dose or drug dose ordered H: on-hand (drug dose on label) V: vehicle- form and amount in which the drug comes

  12. Review • Ratio and Proportion (RP) Known Desired H : V :: D : X means extremes • H & V – known quantities (dose on hand and vehicle) • D & X – the desired dose and the unknown amount to give • Multiply the means and the extremes. • Solve for X

  13. Review • Fractional Equation (FE) H = D V X H:dose on hand V: form in which the drug comes D: desired dosage X: the unknown amount Cross multiply and solve for X

  14. BF: D X V H Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  15. BF: D X V H Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  16. RP: H : V :: D : X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  17. RP: H : V :: D : X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  18. FE: H D V X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  19. FE: H D V X Review • Order: 500 mg ampicillin (Principen), po, bid. • Available: Principen capsules 250 mg

  20. Find the method that works for you and stick with it!

  21. Medication Calculations Step wise approach • Weight inKilograms • Therapeutic dose/range • Concentration/dilution • Rate of Administration • Take the appropriate action based on your calculations KiTCAT

  22. A 42 pound, 6 year old patient, is to receive vancomycin (Vancocin) 382 mg IV every 12 hours. Pharmacy sends a syringe labeled: Vancomycin 380 mg in 100 ml of NS. Drug reference states: Therapeutic dose is 40 mg/kg/24 hours. Concentrations greater than 5 mg/ml are not recommended. A single pediatric dose is given over 60 minutes. The appropriate nursing action would be to • administer the medication at 50 ml/hr. • administer the medication at 100 ml/hr. • notify the physician. • notify pharmacy.

  23. Calculate: KiTCAT • Weight inKilograms • Therapeutic dose/range • Concentration/dilution • Rate of Administration • Take the appropriate action

  24. Conversion Factors • 1 kg = 2.2 lbs. (pounds to kg ÷ ) (kg to pounds X ) • 1 kg = 1000 mg. • 1 lb = 16 oz. • 1 tsp = 5 ml.

  25. Weight inKilograms • Our example: (pounds to kilograms) 42 pounds÷ _____ = _______ kg.

  26. Weight inKilograms • Our example: (pounds to kilograms) 42 pounds÷ _____ = _______ kg.

  27. Weight inKilograms • In the nursery, babies are weighed in grams. • Suppose our patient weighed 3000 grams, what’s the pt weight in kg? • Remember, 1 kg = 1000 grams

  28. Weight inKilograms • Suppose our patient weighed 3000 grams, what’s the pt weight in kg?

  29. Weight inKilograms • Another weight conversion that will be helpful to you is converting lb and ounces to kilograms 16 oz = 1 lb • Convert 14 lb 6 oz to kg

  30. Weight in Kilograms • Convert 14 lb 6 oz to kg

  31. Weight inKilograms • You just weighed a baby at 7.4 kg and the Mom asks you how much her child ‘really’ weighs?

  32. Weight inKilograms • 7.4 kg is how many pounds and ounces?

  33. Practice 15 pounds = _______ kg 53 pounds = _______ kg 4244 grams = ______ kg 598 grams = _______ kg 10 lb 7 oz = _______ kg 14 lb 2 oz = _______ kg 12.8 kg = ______pounds _____ ounces Round to the nearest tenth.

  34. KiTCAT Calculate: • Weight inKilograms • Therapeutic dose/range • Concentration/dilution • Rate of Administration • Take the appropriate action

  35. Therapeutic dose/range • In adults, therapeutic dose = ‘usual dose’ • In most adult cases, the range is already calculated

  36. Therapeutic dose/range • What about pediatrics? • Age

  37. AGE • Infants have: • immature liver and kidney function • (delays metabolism & elimination). • decreased gastric emptying (<3 y.o.) • (alters drug absorption) • lower concentration of plasma proteins • (can cause toxic effects in drugs that bind to proteins) • less total body fat & more total body water • ( lipid-soluble drugs may require lower doses and • water-soluble drugs may require larger doses)

  38. Therapeutic dose/range • Body Mass

  39. BODY MASS • to maintain a desired drug concentration in individuals of various sizes, the drug dose MUST BE adjusted for body mass. • As children grow, changes in fat, muscle, body water, and organ maturity can alter pharmacokinetic effects of drugs. • This is why pediatric doses are measured in mg/kg • Let’s look at vancomycin

  40. What is the PEDIATRIC dose/range? • What is the THERAPEUTIC dose/range for our patient?

  41. What is the PEDIATRIC dose/range? • _____ mg/kg/_____ • What is the THERAPEUTIC dose/range for our 19.1 kg patient? ______mg/24hr

  42. Therapeutic dose/range • What is the THERAPEUTIC RANGE? • _____ to ______ mg/kg/ ________

  43. Therapeutic dose/range • What is the THERAPEUTIC RANGE? • _____ to ______ mg/kg/ ________

  44. Let’s calculate a therapeutic dose/range for our 42 pound patient • Patient weighs ______ kg, so… • ____ kg X ____ mg (min. dose) = ____ mg/day • ____ kg X ____mg (max. dose) = ____ mg/day • Therapeutic dose/range is _____ to _____ mg/DAY

  45. Let’s calculate a therapeutic dose/range for our 42 pound patient • Patient weighs ______ kg, so… • ____ kg X ____ mg (min. dose) = ____ mg/day • ____ kg X ____mg (max. dose) = ____ mg/day • Therapeutic dose/range is _____ to _____ mg/DAY

  46. Triangle method Child’s wt 19.1 kg X X 50 mg (min.) 75 mg (max) (from drug reference) = = 955 mg 1432.5 mg The therapeutic range is: 955 mg to 1432.5 mg/DAY

  47. KiTCAT • Methylprednisolone (Solu-Medrol) 100 mg IV as loading dose, for status asthmaticus. • Patient is 110 lbs • Is this a therapeutic dose?

  48. KiTCAT K: T: • Methylprednisolone (Solu-Medrol) 100 mg IV as loading dose, for status asthmaticus. • 110 lb • Is this a therapeutic dose?

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