1. 18
Dosage Calculations

2. State Standard
22) Calculate correct doses required when given a simulated prescription for a pediatric dose, adult dose, and geriatric dose based on weight (if applicable), length of administration, times per day of administration, and presence of other diseases/disorders.**

3. Objectives Students will be able to…
Calculate the number of doses need for a medication
Calculate the dosage needed of a medication
Calculate the days supply for a medication

4. Dosage Calculation
Pharmacy calculations pertaining to the number of doses, dispensing quantities, and/or ingredient quantities.
Solve dosage calculations by setting up ratios and proportions, keeping like units consistent, and cross-multiplying to solve for the unknown.

5. SIG Code Refresher qd = every day qod = every other day
bid = twice a day
tid = three times a day
qid = four times a day
q4h = every 4 hours, or six times a day
q6h = every 6 hours, or four times a day

6. SIG Code Refresher q8h = every 8 hours, or three times a day
q12h = every 12 hours, or twice a day
q4–6h = every 4 to 6 hours, or four to six times a day
prn = as needed

7. Calculating the Number of Doses
The amount of medication prescribed to be taken at one time
Determine which information presented is actually applicable to the question.
Quantity dispensed
Use ratio/proportion and solve for X.

8. Figure 18-1 Drug label for fluoxetine hydrochloride oral solution.

9. Figure 18-3 Prescription for lipitor.

10. Figure 18-4 Drug label for erythromycin.

11. Figure 18-5 Prescription for vicodin.

12. Calculating the Quantity to Disperse
Dispensing quantity
The total amount of medication to be dispensed
Determine which information is necessary.
Dose
Frequency
Duration

13. Calculating the Quantity to Disperse
Formula
Dose × frequency × duration = quantity to dispense

14. Figure 18-8 Prescription for biaxin.

15. Figure 18-11 Drug label for diazepam.

16. Figure 18-12 Prescription for Lasix.

17. Figure 18-14

18. Calculating the Quantity of Ingredient
Often calculated when preparing compounded preparations
Determine which information is necessary.
Dose
Drug name and strength

19. Calculating the Quantity of Ingredient
Use ratio/proportion equation with the dose and strength.
Units of measurement must be the same.

20. Figure 18-15 Drug label for codeine phosphate.

21. Figure 18-15 (continued) Prescription for codeine phosphate.

22. Figure 18-17 Drug label for fentanyl.

23. Figure 18-18 Drug label for dexamethasone.

24. Calculating the Correct Days Supply
Expected duration for a prescription being dispensed; how long the amount of medication dispensed will last if taken as directed

25. Calculating the Correct Days Supply
The information required to solve this equation is:
Dose
Frequency
Quantity to dispense

26. Calculating the Correct Days Supply
The days supply is equal to the total dose, divided by the product of the dose and the dose frequency.

27. Figure 18-19 Prescription for pamelor.

28. Figure 18-22 Drug label for cefaclor.

29. Figure 18-23 Prescription for depakote.

30. Figure 18-24 Prescription for keflex.

31. Figure 18-25 Prescription for ceclor.

32. Solving Multiple Dosage Calculations
What is the appropriate quantity to dispense?
How many total doses are to be dispensed?
What is the total amount of medication to be dispensed?
How many days should this prescription last?

33. Figure 18-26 Prescription for dexamethasome.

34. Figure 18-27 Prescription for proventil.

35. Figure 18-28

36. Figure 18-29 Prescription for xanax.

37. Activity Complete drug cards for the following…
Allopurinol (Zyloprim)
Penicillin (Pen VK)
Sitagliptin (Januvia)
Individually complete the Oral Dosages Worksheet

38. Pediatric Dosage Calculations

39. State Standard
22) Calculate correct doses required when given a simulated prescription for a pediatric dose, adult dose, and geriatric dose based on weight (if applicable), length of administration, times per day of administration, and presence of other diseases/disorders.**

40. Objectives Students will be able to..
Convert weight from pounds to kilograms
Calculate pediatric dosages using size and body weight

41. Calculating Pediatric Dosages
Require special dosing adjusted for age and body weight

42. Calculating Pediatric Dosages
Three primary systems
Fried's Rule
Calculates pediatric dosages based on the child's age in months
Young's Rule
Uses a formula based on the child's age expressed in years
Clark's Rule
Based on the patient's weight, expressed in pounds

43. Calculating Pediatric Dosages
Example
15 months old infant
Weighs 20 pounds
Needs streptomycin sulfate
Usually administered to adults as 1 gm (1,000 mg) in a daily IM injection. What is the appropriate dosage for the infant?
Do the different rules result in the same dosage?

44. Calculating Pediatric Dosages
Fried's rule
Pediatric dose

45. Calculating Pediatric Dosages
Fried's rule
Pediatric dose = 0.1 × 1,000
Pediatric dose = 100 mg
Fried's rule results in 100 mg dose

46. Calculating Pediatric Dosages
Young's Rule (for the same child)
Note that 15 months =1.25 years
Pediatric dose

47. Calculating Pediatric Dosages
Young's Rule (for the same child)
Pediatric dose = × 1,000
Pediatric dose = 94 mg
Young's rule results in 94 mg dose

48. Calculating Pediatric Dosages
Clark's Rule
Pediatric dose

49. Calculating Pediatric Dosages
Clark's Rule
Pediatric dose = × 1,000
Pediatric dose = 133 mg
Clark's rule results in 133 mg dose

50. Converting Weight from Pounds to Kilograms
Divide pounds by 2.2
Example: If the infant weighs 20 pounds, what is her weight in kg?
20 lb ÷ 2.2 = 9.09 kg
Multiply kilograms by 2.2
Example: If the infant weighs 8 kg, what is his weight in pounds?
8 kg × 2.2 = 17.6 lb

51. Calculating Dosages Using mg/kg/day
Formula for solving dosage calculations based on the patient's weight in kilograms
Most precise system of dosage
Based on the number of milligrams suggested per kilogram per day
Preferred method for calculating pediatric dosages

52. Summary
Dosage calculations are the pharmacy calculations most often performed by pharmacy technicians.
Dosage calculations include determining number of doses, dispensing quantities, amount of active ingredients, both adult and pediatric patients.

53. Activity Complete drug cards for the following…
Amitriptyline (Elavil)
Clonidine (Catapres)
Latanoprost (Xalatan)
Individually complete the pediatric dosage calculations activity on the class website.