Dosage Calculations

Dosage Calculations

After completing this chapter, youshould be able to:

• Solve one-step pharmaceuticaldosage calculations.

• Set up a series of ratios andproportions to solve a singledosage calculation.

• Determine what informationyou will need to solve for, inaddition to any giveninformation, to properlycalculate dosages.

• Convert pediatric weights frompounds to kilograms.

• Accurately determine dosagesbased on mg/kg/day.

• Define common sig (signa)codes used on prescriptions.

INTRODUCTIONProper dosing of medications is important to ensure patientsafety. Calculating dosages, dosage regimens, andcompounding formulas involves the use of simple mathprinciples. You can solve many of these problems by settingup ratios and proportions using the information given in thequestion and keeping like units consistent.

CHAPTER

5

2

L earning Objectives

Joh_Ch05.qxd 8/31/07 2:39 PM Page 2

Chapter Five Dosage Calculations 3

Sig RefresherThe sig portion of the prescription order, meaning signa, is where the instruc-tions for the patient are written. Pharmacy technicians enter the informationfrom the prescription order into the computer. The sig is an important valueto remember in order to properly determine pediatric dosages. The followingare 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 CalculationsDosage calculations include calculating the number of doses, dispensingquantities, and ingredient quantities; these calculations are performed in thepharmacy 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 andprinciples introduced in the previous chapters of this book. You can solvethese calculations by setting up ratios and proportions, keeping like unitsconsistent, and cross-multiplying.

CALCULATING THE NUMBER OF DOSESTo calculate the number of doses, you should first determine which informa-tion presented is actually applicable to the question. Too often mistakes aremade on dosage calculations because we overcomplicate them.

EXAMPLE 5.1 How many 1-tsp doses are in a 4 oz bottle of Prozac® LiquidSolution 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 amountbeing dispensed. The strength of the drug, frequency of dosage and quantityof the stock bottle have no relevance in performing this calculation.

So now we know that we are working with 1 tsp. doses and a total quan-tity of 4 oz, but to solve this calculation using a ratio/proportion we have tohave similar units of measure—in this case mL.

We know that 1 tsp = 5 mL and we should also know that 4 oz. = 120 mL,but if you didn’t that could also be solved by using a ratio/proportion.

Cross-multiply and solve the equation for .

Now that you have both quantities converted to units in mL, we can setup our ratio/proportion and solve.

Cross-multiply

5 * x = 5x and 1 * 120 = 120

1 dose

5 mL=

x doses

120 mL

(1)x = 120

30 * 4 = 120 and 1 * x = (1) x

x

1 oz

30 mL=

4 oz

x mL

..TT

Figure 5-1 Drug label for Prozac.(Courtesy of Eli Lilly and Company.)



Now set up your equation and solve for x.

To solve for x, divide both sides by 5.

So, there are 24 doses (of 5 mL) in a 4 oz (120 mL) bottle.

CALCULATING THE NUMBER OF DOSESEXAMPLE 5.2 How many doses are provided in the prescription below?

Rx—Ibuprofen 400 mg

- po q 6 hr prn pain

Disp. # 120

Let’s look at the information that has been provided:

✓ - po—the dose

✘ q 6 hr prn pain—the frequency

✓ 120—the quantity dispensed

✘ Ibuprofen 400 mg—the drug name and strength

Workplace Wisdom Always use the higher dosage amount when perform-ing dosage calculations on prescriptions that have a range for the dose, as inExample 5.2. This will provide the most conservative solution and ensurethe most accurate potential for days supply.

Using the information provided, set up the ratio/proportion and solve.

Cross-multiply

Now set up your equation and solve for .

To solve for , divide both sides by 2.

So, there is a minimum of 60 doses prescribed.

x = 60 120 , 2 = 60

2x

2=

120

2

x

2x = 120

x

2 * x = 2x and 1 * 120 = 120

1 dose

2 tabs=

x doses

120 tabs

..TT

.T

..TT

.T

x = 24 120 , 5 = 24

2x

2=

120

2

5x = 120



PRACTICE PROBLEMS 5.11. How many dosages are provided in the prescription listed below?

________________

Rx—Cardura® 2 mg

po qd

Disp. # 90

2. How many droppersful (a 2.5 mL dosage) are in a 50 mL bottle ofEryPed® Drops? ________________

..TT

3. How many dosages are provided in the prescription listed below?_____________________

Rx—Vicodin® 5/500

po q8hr

Disp. # 50

4. How many 1 tsp doses are in each bottle of Zithromax® 200 mg/5 mL aslisted below, when mixed? ________________

..TT

5. How many dosages are provided in the prescription listed below?________________

Rx—Regular Insulin U-100 (100 units/mL)

Inject 20 units qAM

Disp. # 1 vial (10mL)

Figure 5-2 Drug label for EryPed Drops.(Reproduced with permission of Abbott Laboratories.)

Figure 5-3 Drug label for Zithromax.(Registered Trademark of Pfizer Inc. Reproduced with permission.)



CALCULATING THE QUANTITY TO DISPENSEEXAMPLE 5.3 How many Biaxin® 250 mg tablets should be dispensed?

Rx—Biaxin® 250 mg

po BID � 10d..TT

Figure 5-4 Drug label for Biaxin.(Reproduced with permission of Abbott Laboratories.)

Again, to solve this dosage calculation it is important to first determinewhich information is necessary; it is also critical to know the common SIGcodes to perform dosage calculations.

Let’s look at what information that has been provided:

✓ po—the dose

✓ BID—the frequency

✓ x 10d—the duration

✘ Biaxin® 250 mg—the drug name and strength

✘ 100 tablets—the quantity of the stock bottle

To calculate the appropriate quantity to dispense, use the following formula:

dose � frequency � duration � quantity to dispense

Using the information provided in the prescription, you can set up thecalculation as such:

1 � 2 � 10 � xdose frequency duration quantity to dispense

1 � 2 � 10 � 2020 � x

So, 20 tablets of Biaxin® 250 mg should be dispensed.

..TT



CALCULATING THE QUANTITY TO DISPENSEEXAMPLE 5.4 How much Promethazine w/Codeine syrup should be dispensed?

Rx—Promethazine w/Codeine Syrup 6.25/10

tsp. po QID � 4d

Let’s look at what information has been provided:

✓ tsp. po—the dose

✓ QID—the frequency

✓ x 4d—the duration

✘ Promethazine w/Codeine Syrup 6.25/10—the drug name and strength

To calculate the appropriate quantity to dispense, use the following formula:

dose � frequency � duration � quantity to dispense

Using the information provided in the prescription, you can set up thecalculation as such:

1tsp � 4 � 4 � xdose frequency duration quantity to dispense

1 � 4 � 4 � 1616 � x

So, 16 teaspoonsful, or 80 mL, of promethazine w/codeine should bedispensed.

PRACTICE PROBLEMS 5.21. What quantity should be dispensed for the prescription listed below?

________________Rx—Zoloft® 50 mg

po qd

Disp. 1 mo. supply

2. What quantity should be dispensed, using the stock medication below,to provide 20 mg of diazepam prior to the procedure and 10 mgfollowing? ________________

..TT

..TT

..TT

Figure 5-5 Drug label forDiazepam.(Used with permission ofRoxane Laboratories, Inc.)



5. What quantity should be dispensed for a 30-day supply of the followingprescription? ________________

Rx—Soma® 350 mg

po BID – TID prn muscle spasms

CALCULATING THE QUANTITY OF INGREDIENTEXAMPLE 5.5 How much codeine is in each dose of Codeine Phosphate Oral

Solution 15 mg/mL?

Rx—Codeine Oral Soln. 15 mg/mL

tbsp po prn pain

Disp. # 4 oz

..TT

..TT

Figure 5-7 Drug label forCodeine Phosphate OralSolution.(Used with permission ofRoxane Laboratories, Inc.)

3. What quantity should be dispensed for a three-month supply of thefollowing prescription? ________________

Rx—furosemide 20 mg

po QOD

4. What quantity should be dispensed if 50 mg of amitriptyline has beenprescribed daily for 3 weeks, if the medication listed below is all that isavailable? ________________

..TT

Figure 5-6 Drug label for Amitriptyline HCL.(Courtesy of Geneva Pharmaceuticals.)



Let’s first look at all of the information provided to determine which willbe used in solving the problem:

✓ tbsp po—the dose✘ prn—the frequency✘ 4 oz—the quantity to dispense✓ Codeine Phosphate Oral Solution 15 mg/mL—the drug name

and strength✘ 500 mL—the quantity of the stock bottle

To solve this problem, we need to set up a ratio/proportion using the doseand strength, but again remember that units of measure must be the same.The dose (1 tbsp) is equivalent to 15 mL—which you should know.

Now we can set up the ratio/proportion.

Cross-multiply and then set up the equation to solve for x.

Now divide both sides by 5 to solve for x.

So, the answer is 45 mg of codeine in each 1 tbsp dose.

PRACTICE PROBLEMS 5.3Perform the following dosage calculations.

1. Promethazine with codeine syrup contains 6.25 mg promethazine and10 mg codeine per 5 mL. How many milligrams of promethazine are in2 tsp? ________________

2. Rx hydroxycobalamine 10,000 mcg/cc 30 cc Sig: 1 cc IM hs

How many milligrams are in each dose?________________

3. Rx acetaminophen with codeine#3 acetaminophen 300 mg/codeine 30 mg 30 tablets

How many grains of codeine are in each tablet? ________________

CALCULATING THE QUANTITY OF INGREDIENTEXAMPLE 5.6 How many mL of stock Dopamine must be added to the IV solution?

Rx—Dopamine 400 mg added to 500 mL of NS

Stock: Dopamine HCl Injection 80 mg/mL

x = 45

5x

5=

225

5

5x = 225

15 * 15 = 225 and 5 * x = 5x

15 mg

5 mL=

15 mg

1 mL

..TT

Joh_Ch05.qxd 8/31/07 2:39 PM Page 10

Let’s first look at all of the information provided to determine which willbe used in solving the problem:

✓ 400 mg—the dose

✘ 500 mL—the quantity to dispense

✓ Dopamine HCl Injection 80 mg/mL—the drug name and strength

To solve this problem, we must determine how many milliliters of the stockDopamine will need to be added to the normal saline IV solution bag.

We must set up a ratio/proportion.

Cross-multiply and then set up the equation to solve for x.

Now divide both sides by 80 to solve for x.

So, the answer is 5 mL of the stock Dopamine HCl Injection must beadded to the IV solution.

PRACTICE PROBLEMS 5.4

1. Z-Pak®s contain 6 tablets of azithromycin 250 mg, which is taken overthe course of five days. How many total mg of active ingredient arecontained in a Z-Pak®? ________________

2. How many mcg of Fentanyl® would be contained in 1.5 mL?________________

x = 5

400

80=

80x

80

400 = 80x

1 * 400 = 400 and 80 * x = 80x

80 mg

1 mL=

400 mg

x mL


Figure 5-8 Drug label forFentanyl.(Courtesy of ESI Lederle, a BusinessUnit of Wyeth Pharmaceuticals,Philadelphia, PA.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 11

3. How many milligrams of acetaminophen are contained in 2 Lortab 2.5 (2.5 mg hydrocodone/500 mg acetaminophen)® tablets? ____________

4. How many milligrams of dexamethasone are contained in the stockbottle (500 mL) below? ________________


5. How many mg of hydrocortisone are found in 1 tbsp of Cortef ®

10 mg/5 mL? ________________

Figure 5-10 Drug label forCortef.(Courtesy of PharmaciaCorporation.)

Figure 5-9 Drug label forDexamethasone Oral Solution.(Used with permission of RoxaneLaboratories, Inc.)

CALCULATING THE CORRECT DAYS SUPPLYEXAMPLE 5.7 How many days should the following prescription last?

Rx—Pamelor® 75 mg

po BID

Disp. # 50

..TT

Joh_Ch05.qxd 8/31/07 2:39 PM Page 12


Figure 5-11 Drug label for Pamelor.(Copyright Novartis Pharmaceuticals Corporation. Reprinted with permission.)

Let’s determine which information provided will be needed to solve theproblem.

✓ po—the dose

✓ BID—the frequency

✓ 50—the quantity to dispense

✘ Pamelor® 75 mg—the drug name and strength

✘ 100 capsules—the quantity of the stock bottle

To calculate the appropriate days supply, use the following formula:

Using the information provided, set up the formula as below.

This becomes . . .

So, this prescription should last for 25 days.

CALCULATING THE CORRECT DAYS SUPPLYEXAMPLE 5.8 How many days should the following prescription last?

Rx—Kaletra® 133.3 mg/33.3mg

po BID food.

Disp. # 360

..TT

x =

50

2 or x = 25

x =

50 (qty. dispensed)

(1 * 2) (Dose * Frequency)

Days Supply =

Qty. Dispensed

(Dose * Frequency)

..TT

Joh_Ch05.qxd 8/31/07 2:39 PM Page 13

Let’s determine which information provided will be needed to solve theproblem.

✓ po—the dose✓ BID—the frequency✓ 360—the quantity to dispense✘ Kaletra® 133.3 mg/33.3mg—the drug name and strength

To calculate the appropriate days supply, use the following formula:

Using the information provided, set up the formula as below.

This becomes. . .

So this prescription should last for 3 months, or 90 days.

PRACTICE PROBLEMS 5.51. How many days will the following prescription last? ________________

Rx—Diabinese® 100 mg

po qAM

Disp. # 45

2. How many days will a 150 mL bottle of Ceclor® last, if thepatient is to take 2 teaspoonsful three times daily? ________________

125 mg>5 mL

..TT

x =

3604

or x = 90

x =

360 (qty. dispensed)

(2 * 2) (Dose * Frequency)

Days Supply =

Qty. Dispensed

(Dose * Frequency)

..TT


Figure 5-12 Drug label for Ceclor.(Courtesy of Eli Lilly and Company.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 14


3. How many days will the following prescription last? ________________

Rx—Valium® 5 mg

po BID

Disp. # 60

4. How many days should 10 tablets of Cialis® 5 mg last, if the prescribed directed to use is a maximum of one tablet q3days?________________

5. How many days will the following prescription last? ________________

Rx—Keflex® 250 mg

po TID

Disp. # 42


1. Rx—Amoxil 250 mg/5 mL

tsp TID � 10d

a. What is the appropriate quantity to dispense? ________________

b. How many total doses are to be dispensed? ________________

c. What is the total amount of amoxicillin, in mg, to be dispensed?________________

d. How many days should this prescription last? ________________

2. Rx—Dexamethasone Oral Soln.

Give 0.25 mg QOD

Disp. 6 mg

0.5 mg>5 mL

..TT

..TT

..TT

Figure 5-13 Drug label forDexamethasone OralSolution.(Used with permission ofRoxane Laboratories, Inc.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 15


a. What is the appropriate quantity to dispense?________________


c. What is the total amount of dexamethasone, in mg, to be dispensed?________________


3. Rx—Proventil® Inhaler 17gm (200 inhalations)

Use puffs BID

Disp. # 1



c. What is the total amount of albuterol, in mcg, per inhalation?________________


4. Rx—Xanax 0.25 mg

- TID prn � 14d


b. What is the maximum number of doses available if 60 tablets aredispensed? ________________

c. What is the maximum amount of alprazolam, in mg, to be takendaily? ________________

d. How many days could this prescription last, if 60 tablets aredispensed? ________________

Pediatric DosingPediatric patients, which include both infants and children, require spe-cial dosing that is adjusted for their body weight. A number of formulashave been used throughout the years to determine the best dose for pedi-atric patients, but the most commonly used method is stated as mg/kg ofbody weight.

Pediatric Formulas Children need lower dosages of medication com-pared to adults. Three formulas are used to help calculate a pediatricdosage based on whatever information is available. In some children’s hos-pitals the pharmacy may have a preferred formula. However, the pharmacytechnician should be able to calculate the correct pediatric dosage usingeach formula.

..TT

.T

..TT

Joh_Ch05.qxd 8/31/07 2:39 PM Page 16

CALCULATING PEDIATRIC DOSAGES USING FRIED’S RULEEXAMPLE 5.9 An infant, 15 months old and weighing 20 pounds, needs

Streptomycin Sulfate, which is usually administered to adults as1 gm (1000 mg), as a daily IM injection. What is the appropriatedosage for the infant?

To calculate the pediatric dosage based on a child’s age in months, simplyuse the formula for Fried’s Rule. Using the information provided, you can setup the calculation as follows:

So, according to Fried’s Rule, the pediatric dosage appropriate for a 15-month-old would be 100 mg.

PRACTICE PROBLEMS 5.71. A child, 24 months old, needs acetaminophen, and the normal adult

dose is 650 mg. What is the appropriate dosage for thechild?________________

2. An 18-month-old needs amikacin sulfate, and the normal adult dose is250 mg. What is the appropriate dosage for the child? ________________

3. A child, 30 months old, needs erythromycin, and the normal adult doseis 250 mg QID. What is the appropriate dosage for the child?________________

Pediatric Dose = 100 mg

Pediatric Dose = 0.1 * 1000

Pediatric Dose =

15

150* 1000

Pediatric Dose =

15 (Age in months)

150* 1000 mg (Adult Dose)


FORMULA Pediatric Dosing

Fried’s Rule

Young’s Rule

Clark’s Rule

Child’s dosage =

Child’s weight in pounds

150* Adult dosage

Child’s dosage =

Age of child in years

Age of child in years + 12* Adult dosage

Child’s dosage =

Age in months

150* Adult dosage

Joh_Ch05.qxd 8/31/07 2:39 PM Page 17

CALCULATING PEDIATRIC DOSAGES USING YOUNG’S RULEEXAMPLE 5.10 Now, let’s reexamine Example 5.9 using Young’s Rule, which uses

the child’s age in years. The age of a 15-month-old could beexpressed as 1.25 years old, since he or she has lived for 12 months(1 year) � 3 months (1/4 or 0.25 of a year).

Using an age of 1.25 years and the information provided in Example 5.5,set up the calculation, using Young’s Rule, as follows:

So, according to Young’s Rule, the pediatric dosage appropriate for a15-month-old would be 94 mg.


1. A 2-year-old child is prescribed amoxicillin, and the normal adult dose is500 mg. What is the appropriate dosage for the child?________________

2. A 7-year-old needs propylthiouracil, and the normal adult daily dose is150 mg. What is the appropriate dosage for the child?________________

3. A child, 10 years old, is prescribed Tavist® syrup, and the normal adultdose is 1.34 mg BID. What is the appropriate dosage for thechild?________________

CALCULATING PEDIATRIC DOSAGES USING CLARK’S RULEEXAMPLE 5.11 Now, let’s reexamine Example 5.9 using Clark’s Rule, which uses

the child’s weight in pounds.

Using a weight of 20 pounds and the information provided in Example5.5, set up the calculation, using Young’s Rule, as follows:



Pediatric Dose =

20

150* 1000

Pediatric Dose =

20 (Weight in pounds)

150* 1000 mg (Adult Dose)



Pediatric Dose =

1.25

13.25* 1000

Pediatric Dose =

1.25 (Age in years)

13.25 (Age of child + 12)* 1000 mg (Adult Dose)


Joh_Ch05.qxd 8/31/07 2:39 PM Page 18

So, according to Clark’s Rule, the pediatric dosage, appropriate for a15-month-old, weighing 20 pounds, would be 133 mg.


1. A child, weighing 85 pounds, is prescribed hydrochlorothiazide, andthe normal adult dose is 50 mg. What is the appropriate dosage for thechild?________________

2. A child, weighing 70 pounds, is prescribed quinine sulfate, and thenormal adult dose is 325 mg TID. What is the appropriate dosage forthe child?________________

3. A child, weighing 112 pounds, is prescribed Kaletra®, a proteaseinhibitor combination therapy. The normal adult dose is 400 mglopinavir/100 mg ritonavir. What is the appropriate dosage for thechild?________________

Converting Pediatric WeightTo solve pediatric dosing calculations using the mg/kg method, you mustfirst determine the patient’s weight in kilograms. To convert weight inpounds to kilograms, use the following formula:


FORMULA Weight Conversion

1 kg = 2.2 lb

CONVERTING WEIGHT FROM POUNDS TO KGEXAMPLE 5.12 If the infant weighs 20 pounds, what is his or her weight in kg?

Using the weight conversion formula, you divide the patient’s weight,which in this case is 20, by 2.2 to convert the weight from pounds to kg.

So, the infant weighs 9.09 kg.

EXAMPLE 5.13 If a person weighs 180 lb., divide by 2.2 to find weight inkilograms.

So 180 lb. equals 81.82 kg.

1802.2 = 81.82 kg

20 , 2.2 = 9.09

Joh_Ch05.qxd 8/31/07 2:39 PM Page 19

PRACTICE PROBLEMS 5.10Convert the following.

1. 115 pounds = ________________ kg

2. 18 kg = ________________ pounds

3. 74 pounds = ________________ kg

4. 50 kg = ________________ pounds

5. 41 kg = ________________ pounds

6. 60 pounds = ________________ kg

7. 24 kg = ________________ pounds

8. 100 pounds = ________________ kg

Mg Kg DayWhen the dose is stated in the manufacturer information as mg/kg/day, thismeans we can calculate the patient’s weight in kilograms, multiply the rec-ommended dose, and take into account the number of times per day the doseis to be given. The goal is to determine how many milligrams can be given ineach dose.

Step 1: Determine weight in kilograms.

Step 2: Multiply by the recommended dose.

Step 3: Divide by the number of doses given daily.

CALCULATING DOSAGES USING MG/KG/DAYEXAMPLE 5.14 Using the infant from Example 5.9, determine the pediatric dosage

if it is recommended to administer 20 mg/kg/day (maximum of1gm) of Streptomycin Sulfate.

The infant’s weight in kg has already been calculated as 9.09, so now wewill multiply the recommended number of milligrams by her weight in kilo-grams to calculate the appropriate daily pediatric dosage.

So, according to mg/kg/day, the patient should be given 181.8 mg ofStreptomycin Sulfate as a daily IM injection.

181.8 = Pediatric Daily Dosage

20 * 9.09 * 1 = Pediatric Daily Dosage

20 mg * 9.09 kg * 1 day = Pediatric Daily Dosage

//


Joh_Ch05.qxd 8/31/07 2:39 PM Page 20

Using the patient from Example 5.13, an order is given for a dose statedas 20 mg/kg tid.

Step 1: The weight has been determined to be 81.82 kg.

Step 2: Multiply 81.82 by 20 mg, which equals 1634 mg.

Step 3: Divide the total number of milligrams for the day by the number ofdoses for the day: .

Based on his weight, the patient should receive 544 mg of drug per dose.The patient used in the preceding example weighs 180 lb. and is probably

an adult. The same principles apply to calculating appropriate dosages for achild based on body weight in kilograms.


1. A dose of 4 mg/kg/day of Plaquenil® can be recommended for certainchildren suffering from lupus. What would be the appropriate dosagefor a patient weighing 47 kg? ________________

2. The daily dose of Omnicef®, in children, is 14 mg/kg, up to a maximumdose of 600 mg/day. What is the appropriate daily dosage for a patientwho weighs 98 pounds? ________________

3. The recommended dosage of fluconazole is 6 mg/kg on day one,followed by 3 mg/kg/day for oropharyngeal candidiasis. What are theappropriate dosages for a child weighing 30 kg? ________________

4. A child, weighing 76 pounds, is prescribed the antibiotic, Cefaclor. It isrecommended for children to receive 20 mg/kg/day in divided dosesevery 8 hours. How many mg should the child take per dose?________________

5. Acute lymphatic leukemia in children can respond well to methotrexategiven 2.5 mg/kg every 14 days by IV. What would be the appropriatedosage of methotrexate to administer biweekly to a child weighing110 pounds? ________________

PRACTICE PROBLEMS 5.12Perform the following pediatric dosage calculations.

1. Rx tetracycline 25 mg/kg in four equal dosesYour patient is 10 years old and weighs 88 lb.

a. What is the patient’s weight in kilograms? ________________

b. What is the total dosage for this prescription?________________

c. How much is each dose? ________________

1634 mg>3 = 544 mg


Joh_Ch05.qxd 8/31/07 2:39 PM Page 21

2. Rx amoxicillin/potassium clavulanate 45 mg/kg/day q12hYour patient is 6 years old and weighs 68 lb.


b. What is the total dosage per day? ________________


3. Rx furosemide daily

Your patient is 3 years old and weighs 22 lb.


b. What is the daily dose? ________________

4. Rx albuterol oral syrup 2 mg/5 mL 0.2 mg/kg/day in three divideddoses





5. Rx amantadine 6.6 mg/kg/day in two doses, not to exceed 150 mgper day





SUMMARYDosage calculations are varied, and more than likely will be the pharmacycalculations you perform most often. Dosage calculations include determin-ing the number of doses, dispensing quantities, and ingredient quantities, forboth adult and pediatric patients.

1 mg>kg


Joh_Ch05.qxd 8/31/07 2:39 PM Page 22


CHAPTER REVIEW QUESTIONS

CHAPTER

5

MULTIPLE CHOICE1. How many 1-tsp doses are in 1 qt. of lactulose

solution, USP 10 g/15 mL?________________

a. 32 doses c. 128 doses

b. 64 doses d. 192 doses

2. How many milligrams of estradiol are deliveredover 72 hours by one 0.075 mg/daypatch?________________

a. 0.225 mg c. 8 mg

b. 1.6 mg d. 0.075 mg

3. You are asked to compound maldroxyl 60 mL,diphenhydramine elixir 60 mL, and viscous li-docaine 2%, qs to 200 mL. How much viscouslidocaine 2% will you need to prepare theorder?________________

a. 60 mL c. 80 mL

b. 4 mL d. 200 mL

4. The recommended pediatric dose of ampicillinis 25 mg/kg/day q8h. Your patient is a 4-week-old infant who weighs 8.7 pounds. Which is thebest dose for this patient? ________________

a. 15 mg c. 33 mg

b. 25 mg d. 45 mg

5. How many days will 4 oz. of clemastine fumer-ate syrup 0.5 mg/5 mL last if the dose is tspdaily?________________

a. 24 days c. 30 days

b. 48 days d. 60 days

6. How many grams of drug are in 480 mL ofdocusate sodium syrup 60 mg/15 mL?________________

a. 28.8 g c. 1920 g

b. 1.92 g d. 2.88 g

1/2

7. How many milligrams are in a 2-mL dose ofprochlorperazine injection 5 mg/mL given IMfor severe nausea and vomiting?________________

a. 10 mg c. 2.5 mg

b. 5 mg d. 15 mg

8. How many milliliters of chloral hydrate syrup500 mg/5 mL are required for a dose of 100 mg?________________

a. 2.5 mL c. 2 mL

b. 5 mL d. 1 mL

9. The recommended pediatric dose for promet-hazine is 0.25 mg/kg qid. What is the bestdose for a 12-year-old male who weighs 95 lb?________________

a. 2.5 mg c. 12.5 mg

b. 10 mg d. 15 mg

10. How many total grams of active ingredient arein five syringes of testosterone 4 g/100 g topicalgel containing 3 g of gel each? What is the percent strength of the final product?________________

a. 15 g, 0.4% c. 2.4 g, 40%

b. 0.6 g, 4% d. 60 g, 0.04%

TRUE OR FALSE11. When solving dosage calculations, it is helpful

to look for the given. ________________

a. true b. false

12. When setting up ratios and proportions to solvedosage calculations, it is best to keep like unitsconsistent. ________________

a. true b. false

Joh_Ch05.qxd 8/31/07 2:39 PM Page 23


13. The unknown, x, will always be located in theupper left corner when setting up dosagecalculations. ________________

a. true b. false

14. When choosing the answer in a multiple-choicequestion, you should find the numerical answerregardless of units. ________________

a. true b. false

15. You can solve most dosage calculations bycross-multiplying. ________________

a. true b. false

SHORT ANSWER

16. Describe why proper dosing of medications isimportant to ensure patient safety.________________

17. Name three types of dosage forms.________________ ___________ ___________

18. Which dose is larger, 4 mg/mL or 1 mL of 4%gel? ________________

19. How many milligrams of drug are in 0.5 mL ofa cream that is 4 mg/mL? ________________

20. How many milliliters will be required to pro-vide the necessary dose of albuterol oral syrup2 mg/5 mL to be given 0.2 mg/kg/day tid for apatient who weighs 88 lb.? ________________

Joh_Ch05.qxd 8/31/07 2:39 PM Page 24

Dosage Calculations

Documents