18 Dosage Calculations

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.**

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

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.

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

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

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.

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

Figure 18-3 Prescription for lipitor.

Figure 18-4 Drug label for erythromycin.

Figure 18-5 Prescription for vicodin.

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

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

Figure 18-8 Prescription for biaxin.

Figure 18-11 Drug label for diazepam.

Figure 18-12 Prescription for Lasix.

Figure 18-14

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

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

Figure 18-15 Drug label for codeine phosphate.

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

Figure 18-17 Drug label for fentanyl.

Figure 18-18 Drug label for dexamethasone.

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

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

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.

Figure 18-19 Prescription for pamelor.

Figure 18-22 Drug label for cefaclor.

Figure 18-23 Prescription for depakote.

Figure 18-24 Prescription for keflex.

Figure 18-25 Prescription for ceclor.

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?

Figure 18-26 Prescription for dexamethasome.

Figure 18-27 Prescription for proventil.

Figure 18-28

Figure 18-29 Prescription for xanax.

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

Pediatric Dosage Calculations

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.**

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

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

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

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?

Calculating Pediatric Dosages Fried's rule Pediatric dose

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

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

Calculating Pediatric Dosages Young's Rule (for the same child) Pediatric dose = 0.094 × 1,000 Pediatric dose = 94 mg Young's rule results in 94 mg dose

Calculating Pediatric Dosages Clark's Rule Pediatric dose

Calculating Pediatric Dosages Clark's Rule Pediatric dose = 0.133 × 1,000 Pediatric dose = 133 mg Clark's rule results in 133 mg dose

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

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

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.

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