Conversions and Calculations Used by Pharmacy Technicians

Copyright © 2007, 2004 by Saunders, an imprint of Elsevier Inc. All rights reserved. 1

Chapter 4Chapter 4

Conversions and Calculations Conversions and Calculations Used by Pharmacy Used by Pharmacy

TechniciansTechnicians


IntroductionIntroduction

The ability to manipulate conversions is a The ability to manipulate conversions is a required competency of pharmacy required competency of pharmacy technicianstechnicians

It is a foundation for filling orders and It is a foundation for filling orders and calculating dosages in the pharmacycalculating dosages in the pharmacy

All transcribing calculations need to be All transcribing calculations need to be checked by a pharmacistchecked by a pharmacist


Introduction Introduction (Continued)(Continued)

Pharmacy measurements come from Pharmacy measurements come from different regions of the worlddifferent regions of the world

The four most common types of The four most common types of calculation systems are:calculation systems are: Metric systemMetric system Household measurementsHousehold measurements Apothecary systemApothecary system Avoirdupois systemAvoirdupois system


Introduction Introduction (Continued)(Continued)

A good way to become familiar with A good way to become familiar with common pharmacy measurements is common pharmacy measurements is to start with what you know and then to start with what you know and then slowly build on that knowledgeslowly build on that knowledge

The pharmacy technician must translate The pharmacy technician must translate the doctor’s orders into lay termsthe doctor’s orders into lay terms

You must make the instructions easy You must make the instructions easy enough for a child to understandenough for a child to understand


ObjectivesObjectives

DDescribe the differences among the escribe the differences among the following measurement systems:following measurement systems: Apothecary systemApothecary system Avoirdupois systemAvoirdupois system Metric systemMetric system Common household measurementsCommon household measurements


Objectives Objectives (Continued)(Continued)

Convert Arabic numbers into Roman Convert Arabic numbers into Roman numerals.numerals.

DDemonstrate the ability to convert among emonstrate the ability to convert among the following measurement systems the following measurement systems commonly used on prescriptions:commonly used on prescriptions: Metric systemMetric system Apothecary systemApothecary system Household systemHousehold system



Use mathematical calculations to Use mathematical calculations to determine dosagedetermine dosage:: Ratios/proportionsRatios/proportions FractionsFractions PercentagesPercentages



Demonstrate the ability to set up Demonstrate the ability to set up equations and solve problems for the equations and solve problems for the following:following: Determining day’s supplyDetermining day’s supply Pediatric dosagesPediatric dosages Drip ratesDrip rates AlligationAlligation Percent dosagesPercent dosages


Metric SystemMetric System

Used throughout pharmacy because of its Used throughout pharmacy because of its accuracyaccuracy

Metric units include:Metric units include: Milliliters, cubic centimeters, and liters for Milliliters, cubic centimeters, and liters for

volumevolume Kilograms, grams, milligrams, and Kilograms, grams, milligrams, and

micrograms for weightmicrograms for weight Millimeters and meters for distanceMillimeters and meters for distance


Metric System Metric System (Continued)(Continued)

There is a 1000-unit difference between There is a 1000-unit difference between each measurementeach measurement

Most Common Metric MeasurementsMost Common Metric Measurements

kgkg____________gg________________mgmg________________mcgmcg

1000x1000x 1000x1000x 1000x1000x


Metric System Metric System (Continued)(Continued)

The use of millimeters is reserved for drug The use of millimeters is reserved for drug calculations based on body surface areascalculations based on body surface areas

Knowing the basics for volume and weight Knowing the basics for volume and weight conversions is adequateconversions is adequate


Household MeasurementsHousehold Measurements

The most common measurement system still The most common measurement system still used in the United States is the household used in the United States is the household systemsystem

Measurements come in a variety of unitsMeasurements come in a variety of units

Volume refers to liquidsVolume refers to liquids Weight refers to dry ingredientsWeight refers to dry ingredients Length refers to distanceLength refers to distance Most common measurement is the teaspoonMost common measurement is the teaspoon


Common Household MeasurementsCommon Household Measurements

HouseholdHousehold MeasurementsMeasurements MetricMetric (Volume)(Volume) (Volume)(Volume) HouseholdHousehold1 teaspoon1 teaspoon 5 ml or cc*5 ml or cc* 1 teaspoon1 teaspoon1 tablespoon1 tablespoon 15 ml or cc15 ml or cc 3 teaspoons3 teaspoons1 cup1 cup 240 ml or cc240 ml or cc 8 ounces8 ounces1 pint1 pint 480 ml or cc480 ml or cc 2 cups2 cups1 quart1 quart 960 ml or cc960 ml or cc 4 cups4 cups1 gallon1 gallon 3840 ml or cc3840 ml or cc 16 cups16 cups

or 3.84 Lor 3.84 L*Remember that 1 ml and 1 cc contain the same amount of liquid.*Remember that 1 ml and 1 cc contain the same amount of liquid.


Apothecary SystemApothecary System

Originated in EuropeOriginated in Europe Units used in this system are grains and Units used in this system are grains and

scruples for dry weightscruples for dry weight Drams and minims for liquidsDrams and minims for liquids More common measurements include More common measurements include

ounces and poundsounces and pounds


Apothecary WeightsApothecary Weights

Dry WeightDry Weight Fluid WeightFluid Weight1 grain 1 grain = = 60 mg60 mg 1 dram1 dram = 60= 60

15 grains15 grains = = 1 gram1 gram 8 drams8 drams = 480= 48020 grains20 grains = = Э Э 11 3 scruples*3 scruples* = 1= 11 dram 1 dram = = ЭЭ 3 31 ounce 1 ounce = = 8 or8 or

= = ЭЭ 24 24= = gr 480gr 480= = 31.1 grams31.1 grams

1 pound1 pound = = 16 ounces16 ounces= = 9696== ЭЭ 288 288= = gr 5760gr 5760= = 454 grams454 grams

*Scruples and minims are not commonly used units*Scruples and minims are not commonly used units


Conversion Table: Conversion Table: Apothecary/Metric/HouseholdApothecary/Metric/Household

Apothecary Apothecary Apothecary Apothecary MetricMetric MetricMetric Common Common VolumeVolume WeightWeight VolumeVolume WeightWeight HouseholdHousehold

11 11 30 ml30 ml 30 g30 g 2 tbsp2 tbsp

44 44 15 ml15 ml 15 g15 g 1 tbsp1 tbsp

22 22 7.5 ml 7.5 ml 7.5 g 7.5 g ½ tbsp½ tbsp

11 gr 60 gr 60 4 ml 4 ml 4 g 4 g 1 tsp1 tsp

½½ gr 30 gr 30 2 ml 2 ml 2 g 2 g ½ tsp½ tsp


Avoirdupois SystemAvoirdupois System

Originated in EnglandOriginated in England Similar to the apothecary system because Similar to the apothecary system because

it also uses grains, ounces, and pounds for it also uses grains, ounces, and pounds for weightweight

For avoirdupois and metric equivalents, For avoirdupois and metric equivalents, refer to Table 4-3refer to Table 4-3


Important Differences Among SystemsImportant Differences Among Systems

The metric system is used for compounding The metric system is used for compounding drugsdrugs

There are differences among manufacturer’s There are differences among manufacturer’s products and their weightsproducts and their weights

Conversions with these variances are Conversions with these variances are approximateapproximate

A pint can be 473 ml, 480 ml, or 500 mlA pint can be 473 ml, 480 ml, or 500 ml 1 pound = 454 g in metric, but only 373 g in the 1 pound = 454 g in metric, but only 373 g in the

apothecary systemapothecary system


Writing Units Using Each SystemWriting Units Using Each System

All four systems will be used in writing All four systems will be used in writing prescriptions, but pharmacies primarily prescriptions, but pharmacies primarily use the metric systemuse the metric system

Regardless of what system is used in a Regardless of what system is used in a prescription, it must be converted to the prescription, it must be converted to the household systemhousehold system


Writing Units Using Each SystemWriting Units Using Each System (Continued)(Continued)

Metric measurementsMetric measurements cc and ml can be used interchangeablycc and ml can be used interchangeably Dry weights use mcg, mg, g, and kgDry weights use mcg, mg, g, and kg Liquid volumes use ml and LLiquid volumes use ml and L



Apothecary measurementsApothecary measurements Dry weights use pounds, ounces, drams, Dry weights use pounds, ounces, drams,

scruples, and grainsscruples, and grains Liquid volume weights use gallons, pints, Liquid volume weights use gallons, pints,

fluid ounces, fluid drams, and minimsfluid ounces, fluid drams, and minims



Avoirdupois measurementsAvoirdupois measurements Dry weights using pounds, ounces, and Dry weights using pounds, ounces, and

grainsgrains


ConversionsConversions

Metric system slideMetric system slide When converting metric measurements When converting metric measurements

from one unit to another you need to move from one unit to another you need to move the decimal either to the right or to the leftthe decimal either to the right or to the left

All changes of the metric system involve All changes of the metric system involve either dividing or multiplying by tenseither dividing or multiplying by tens

Each unit is a multiple of 1000Each unit is a multiple of 1000


Conversions Conversions (Continued)(Continued)

By moving the decimal three spaces (to By moving the decimal three spaces (to the right or left), you can change between the right or left), you can change between these unitsthese units

Remember the difference between 1 kg, 1 Remember the difference between 1 kg, 1 g, 1 mg, and 1 mcg is 1000g, 1 mg, and 1 mcg is 1000



Method A for determining metric Method A for determining metric conversionsconversions

LeftLeft RightRightLargestLargest SmallestSmallest11________________11______________11__________________11______________

1000 kg1000 kg 1000 g 1000 mg mcg 1000 g 1000 mg mcg 1 kg1 kg 1000 g 1,000,000 mg 1000 g 1,000,000 mg 1,000,000,000 1,000,000,000

mcgmcg



Decimals are not placed at the end of a Decimals are not placed at the end of a number unless there is a fraction, such as number unless there is a fraction, such as 1.1 kg1.1 kg

Decimals and periods have been the main Decimals and periods have been the main source of mistakes in pharmaciessource of mistakes in pharmacies



Method B: Large number to small numberMethod B: Large number to small number Don’t divide—multiplyDon’t divide—multiply When converting from large to small, you When converting from large to small, you

multiplymultiply When converting from small to large, you When converting from small to large, you

dividedivide



FractionsFractions There is a two-step process for converting There is a two-step process for converting

fractions into percentagesfractions into percentages Percentage is always a portion of 100Percentage is always a portion of 100 To convert a decimal into a percentage To convert a decimal into a percentage

you simply multiply by 100you simply multiply by 100



PercentagesPercentages Represent a portion of a whole (100)Represent a portion of a whole (100) Used in compoundingUsed in compounding Used to calculate markup on prices, Used to calculate markup on prices,

payment discounts, net profits, gross payment discounts, net profits, gross profitsprofits



Ratio/proportion or formula methodRatio/proportion or formula method Ratios can be considered as parts or Ratios can be considered as parts or

fractionsfractions A concentration of 1:1000 means there is A concentration of 1:1000 means there is

1 part to 1000 parts or 1 g of drug in 1000 1 part to 1000 parts or 1 g of drug in 1000 ml of solutionml of solution



90% of the orders you will encounter in the 90% of the orders you will encounter in the pharmacy will be ratio/proportion equationspharmacy will be ratio/proportion equations

This is three-step process:This is three-step process: Filter out the unnecessary informationFilter out the unnecessary information

Find what strength you have in stock and Find what strength you have in stock and what strength you needwhat strength you need

Set up an equation and double-check the Set up an equation and double-check the calculationscalculations



Two methods:Two methods: Method A: Method A:

(have = need or ratio/proportion)(have = need or ratio/proportion)

Method B: Method B: D / H x Q = Medication to giveD / H x Q = Medication to give

D = desired doseD = desired dose

H = have in stockH = have in stock

Q = quantity neededQ = quantity needed

See Examples 4-2 to 4-6See Examples 4-2 to 4-6


Pediatric DosingPediatric Dosing

When the strength of the medication When the strength of the medication needed cannot be measured with a needed cannot be measured with a teaspoon or is an odd amount, droppers teaspoon or is an odd amount, droppers must be usedmust be used

The pharmacist, not the technician, The pharmacist, not the technician, should show the parent of the patient how should show the parent of the patient how to measure the correct amount to measure the correct amount


Common Liquid Measuring DevicesCommon Liquid Measuring Devices


Determining WeightDetermining Weight

Because all manufacturers provide proper Because all manufacturers provide proper dosing regimens based on kilograms, it is dosing regimens based on kilograms, it is necessary to convert pounds into kilogramsnecessary to convert pounds into kilograms

There are 2.2 pounds per kilogramThere are 2.2 pounds per kilogram16 ounces = 1 lb16 ounces = 1 lb 2.2 pounds = 1 kg2.2 pounds = 1 kgTo determine how many kg in 1 lb, divideTo determine how many kg in 1 lb, divideTo determine how many lbs in 1 kg, multiplyTo determine how many lbs in 1 kg, multiply


Drip RatesDrip Rates

Hospital pharmacy technicians deliverHospital pharmacy technicians delivera 24-hour supply of IV solutions to a 24-hour supply of IV solutions to nursing units dailynursing units daily

Most IV piggybacks are smaller IV Most IV piggybacks are smaller IV solutions that are given over solutions that are given over 30 to 60 minutes30 to 60 minutes

Large volume medications need to be Large volume medications need to be given at a slow rate because the veins given at a slow rate because the veins can only handle a small volumecan only handle a small volume


Drip Rates Drip Rates (Continued)(Continued)

For large volume drips, pharmacy For large volume drips, pharmacy technicians must be able to calculate technicians must be able to calculate the volume needed to last over a certain the volume needed to last over a certain amount of time, or they might need to amount of time, or they might need to calculate how much longer a currently calculate how much longer a currently hanging IV solution will lasthanging IV solution will last


SlideSlideclampclamp

100 ml100 ml

Volume-Volume-controlcontrolchamberchamber

MicrodripMicrodripchamberchamber

RollerRollerclampclamp

Intravenous Intravenous (IV) Drip (IV) Drip SystemSystem



Calculations involve the following:Calculations involve the following: The right amount of drug that is to be The right amount of drug that is to be

given over timegiven over time The amount of time left until an IV runs outThe amount of time left until an IV runs out The amount of drug needed to last a The amount of drug needed to last a

certain amount of timecertain amount of time



Basic conversions are as follows:Basic conversions are as follows: Time:Time: 1 hour = 60 minutes, 1 hour = 60 minutes,

24 hours = 1 day24 hours = 1 day Volume: 5 mL = 60 gttVolume: 5 mL = 60 gtt



Steps involved in determining drops per Steps involved in determining drops per minute:minute: What is the drop factor?What is the drop factor? What will be the milliliters per hour?What will be the milliliters per hour? What will be the milliliters per minute?What will be the milliliters per minute? What will be the drops per minute?What will be the drops per minute?

See Examples 4-12 to 4-14See Examples 4-12 to 4-14


AlligationAlligation

Alligation is used when you need to Alligation is used when you need to prepare (compound) percent strength that prepare (compound) percent strength that you do not have in stockyou do not have in stock


Roman NumeralsRoman Numerals

The number system commonly used in the The number system commonly used in the United States is the Arabic system, United States is the Arabic system, consisting of numbers 1, 2, 3, and so forthconsisting of numbers 1, 2, 3, and so forth

Many physicians use Roman numerals to Many physicians use Roman numerals to indicate the quantity of tablets or capsules indicate the quantity of tablets or capsules to be filled or to order the strength of to be filled or to order the strength of medicationmedication


Roman Numerals Roman Numerals (Continued)(Continued)

When working with Roman numerals, When working with Roman numerals, remember that if a larger number is remember that if a larger number is placed in front of a smaller one, you must placed in front of a smaller one, you must add both to determine the valueadd both to determine the value

However, if a smaller number is placed However, if a smaller number is placed before a larger number, then you must before a larger number, then you must subtractsubtract


International TimeInternational Time

In hospital settings, international time, In hospital settings, international time, also known as military time, is used also known as military time, is used exclusivelyexclusively

Orders are written 24 hours a day and all Orders are written 24 hours a day and all medical-related caretakers must medical-related caretakers must understand exactly when the order was understand exactly when the order was written and when the medication or written and when the medication or treatment is to take placetreatment is to take place


International Time International Time (Continued)(Continued)

The system is based on 100The system is based on 100 Starting with the first hour of the day, the Starting with the first hour of the day, the

clock begins at 0100 (1 clock begins at 0100 (1 AMAM) through 2400 ) through 2400 or 12 midnightor 12 midnight

By using this system there is never any By using this system there is never any question as to when an order was written question as to when an order was written or which order supersedes anotheror which order supersedes another


Military Time ClockMilitary Time Clock

Conversions and Calculations Used by Pharmacy Technicians

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