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# ch05 - Joh_Ch05.qxd 2:39 PM Page 2 CHAPTER 5 Dosage...

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Dosage Calculations After completing this chapter, you should be able to: • Solve one-step pharmaceutical dosage calculations. • Set up a series of ratios and proportions to solve a single dosage calculation. • Determine what information you will need to solve for, in addition to any given information, to properly calculate dosages. • Convert pediatric weights from pounds to kilograms. • Accurately determine dosages based on mg/kg/day. • Define common sig (signa) codes used on prescriptions. INTRODUCTION Proper dosing of medications is important to ensure patient safety. Calculating dosages, dosage regimens, and compounding formulas involves the use of simple math principles. You can solve many of these problems by setting up ratios and proportions using the information given in the question and keeping like units consistent. CHAPTER 5 2 L earning Objectives

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Chapter Five Dosage Calculations 3 Sig Refresher The sig portion of the prescription order, meaning signa , is where the instruc- tions for the patient are written. Pharmacy technicians enter the information from the prescription order into the computer. The sig is an important value to remember in order to properly determine pediatric dosages. The following are some of the more common sigs you will find on prescriptions: qd every day qod every other day d daily bid twice a day tid three times a day qid four times a day q4h every 4 hr q6h every 6 hr q8h every 8 hr q4–6h every 4–6 hr prn as needed Depending on the workplace, you may also see sigs such as the following: q3d every three days qmwf every Monday, Wednesday, and Friday qw every week Dosage Calculations Dosage calculations include calculating the number of doses, dispensing quantities, and ingredient quantities; these calculations are performed in the pharmacy on a daily basis. The pharmacy technician must have a full work- ing knowledge of how to perform these calculations. To perform dosage calculations, you will utilize the information and principles introduced in the previous chapters of this book. You can solve these calculations by setting up ratios and proportions, keeping like units consistent, and cross-multiplying. CALCULATING THE NUMBER OF DOSES To calculate the number of doses, you should first determine which informa- tion presented is actually applicable to the question. Too often mistakes are made on dosage calculations because we overcomplicate them. EXAMPLE 5.1 How many 1-tsp doses are in a 4 oz bottle of Prozac ® Liquid Solution 20 mg/5 mL? Rx Prozac ® Solution tsp. po qd Disp. # 4 oz .. TT = = = = = = = = = = = = = =
4 Chapter Five Dosage Calculations Let’s look at the information that has been provided: tsp po—the dose qd—the frequency 4 oz—the quantity dispensed Prozac ® Solution 20 mg/5 mL—the drug name and strength 120 mL—the quantity of the stock bottle The question is simply asking how many doses make up the total amount being dispensed. The strength of the drug, frequency of dosage and quantity

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ch05 - Joh_Ch05.qxd 2:39 PM Page 2 CHAPTER 5 Dosage...

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