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________________, dosage, many, dose, What, Dosage, appropriate, quantity, should, information, Calculations, Page, 2:39, 8/31/07, Joh_Ch05.qxd, doses, Five, Chapter, solve, days, Pediatric, weight, will, this, prescription, patient, pediatric, following, total, Disp.

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.

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.

L earning Objectives

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

Chapter Five Dosage Calculations 3

Sig Refresher

The sig portion of the prescription order, meaning signa, is where the instructions 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 working 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.

To calculate the number of doses, you should first determine which information 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

Joh_Ch05.qxd 8/31/07 2:39 PM Page 3

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

of 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 quantity of 4 oz, but to solve this calculation using a ratio/proportion we have to

have 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 set

up 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

Figure 5-1 Drug label for Prozac.

(Courtesy of Eli Lilly and Company.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 4

Chapter Five Dosage Calculations 5

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.

EXAMPLE 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 performing dosage calculations on prescriptions that have a range for the dose, as in

Example 5.2. This will provide the most conservative solution and ensure

the 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

2x

x 2x = 120

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

1 dose

2 tabs

x doses

120 tabs

x = 24

2x

5x = 120

Joh_Ch05.qxd 8/31/07 2:39 PM Page 5

6 Chapter Five Dosage Calculations

1. 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 of

EryPed® Drops? ________________

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 as

listed below, when mixed? ________________

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.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 6

Chapter Five Dosage Calculations 7

EXAMPLE 5.3 How many Biaxin® 250 mg tablets should be dispensed?

Rx—Biaxin® 250 mg

po BID 10d

Figure 5-4 Drug label for Biaxin.

(Reproduced with permission of Abbott Laboratories.)

Again, to solve this dosage calculation it is important to first determine

which information is necessary; it is also critical to know the common SIG

codes 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 the

calculation as such:

dose frequency duration quantity to dispense

20 x

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

Joh_Ch05.qxd 8/31/07 2:39 PM Page 7

8 Chapter Five Dosage Calculations

EXAMPLE 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 the

calculation as such:

1tsp 4 4 x

dose frequency duration quantity to dispense

16 x

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

dispensed.

1. 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 mg

following? ________________

Figure 5-5 Drug label for

Diazepam.

(Used with permission of

Roxane Laboratories, Inc.)

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

Chapter Five Dosage Calculations 9

5. What quantity should be dispensed for a 30-day supply of the following

prescription? ________________

Rx—Soma® 350 mg

po BID – TID prn muscle spasms

EXAMPLE 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

Figure 5-7 Drug label for

Codeine Phosphate Oral

Solution.

(Used with permission of

Roxane Laboratories, Inc.)

3. What quantity should be dispensed for a three-month supply of the

following prescription? ________________

Rx—furosemide 20 mg

po QOD

4. What quantity should be dispensed if 50 mg of amitriptyline has been

prescribed daily for 3 weeks, if the medication listed below is all that is

available? ________________

Figure 5-6 Drug label for Amitriptyline HCL.

(Courtesy of Geneva Pharmaceuticals.)

Joh_Ch05.qxd 8/31/07 2:39 PM Page 9

10 Chapter Five Dosage Calculations

Let’s first look at all of the information provided to determine which will

be 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 dose

and 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.

Perform the following dosage calculations.

1. Promethazine with codeine syrup contains 6.25 mg promethazine and

10 mg codeine per 5 mL. How many milligrams of promethazine are in

2 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? ________________

EXAMPLE 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

5x = 225

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

15 mg

5 mL

15 mg

1 mL

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

Let’s first look at all of the information provided to determine which will

be 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 stock

Dopamine 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 be

added to the IV solution.

1. Z-Pak®s contain 6 tablets of azithromycin 250 mg, which is taken over

the course of five days. How many total mg of active ingredient are

contained in a Z-Pak®? ________________

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

x = 5

80x

400 = 80x

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

80 mg

1 mL

400 mg

x mL

Chapter Five Dosage Calculations 11

Figure 5-8 Drug label for

Fentanyl.

(Courtesy of ESI Lederle, a Business

Unit 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 stock

bottle (500 mL) below? ________________

12 Chapter Five Dosage Calculations

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

10 mg/5 mL? ________________

Figure 5-10 Drug label for

Cortef.

(Courtesy of Pharmacia

Corporation.)

Figure 5-9 Drug label for

Dexamethasone Oral Solution.

(Used with permission of Roxane

Laboratories, Inc.)

EXAMPLE 5.7 How many days should the following prescription last?

Rx—Pamelor® 75 mg

po BID

Disp. # 50

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

Chapter Five Dosage Calculations 13

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 the

problem.

✓ 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.

EXAMPLE 5.8 How many days should the following prescription last?

Rx—Kaletra® 133.3 mg/33.3mg

po BID food.

Disp. # 360

x =

or x = 25

x =

50 (qty. dispensed)

(1 * 2) (Dose * Frequency)

Days Supply =

Qty. Dispensed

(Dose * Frequency)

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

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

problem.

✓ 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.

1. 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 the

patient is to take 2 teaspoonsful three times daily? ________________

125 mg>5 mL

x =

or x = 90

x =

360 (qty. dispensed)

(2 * 2) (Dose * Frequency)

Days Supply =

Qty. Dispensed

(Dose * Frequency)

14 Chapter Five Dosage Calculations

Figure 5-12 Drug label for Ceclor.

(Courtesy of Eli Lilly and Company.)

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

Chapter Five Dosage Calculations 15

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 q3

days?________________

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

Figure 5-13 Drug label for

Dexamethasone Oral

Solution.

(Used with permission of

Roxane Laboratories, Inc.)

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

16 Chapter Five Dosage Calculations

a. What is the appropriate quantity to dispense?________________

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

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

d. How many days should this prescription last? ________________

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

Use puffs BID

Disp. # 1

a. What is the appropriate quantity to dispense? ________________

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

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

d. How many days should this prescription last? ________________

4. Rx—Xanax 0.25 mg

- TID prn 14d

a. What is the appropriate quantity to dispense? ________________

b. What is the maximum number of doses available if 60 tablets are

dispensed? ________________

c. What is the maximum amount of alprazolam, in mg, to be taken

daily? ________________

d. How many days could this prescription last, if 60 tablets are

dispensed? ________________

Pediatric Dosing

Pediatric patients, which include both infants and children, require special dosing that is adjusted for their body weight. A number of formulas

have been used throughout the years to determine the best dose for pediatric patients, but the most commonly used method is stated as mg/kg of

body weight.

Pediatric Formulas Children need lower dosages of medication compared to adults. Three formulas are used to help calculate a pediatric

dosage based on whatever information is available. In some children’s hospitals the pharmacy may have a preferred formula. However, the pharmacy

technician should be able to calculate the correct pediatric dosage using

each formula.

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

EXAMPLE 5.9 An infant, 15 months old and weighing 20 pounds, needs

Streptomycin Sulfate, which is usually administered to adults as

1 gm (1000 mg), as a daily IM injection. What is the appropriate

dosage for the infant?

To calculate the pediatric dosage based on a child’s age in months, simply

use the formula for Fried’s Rule. Using the information provided, you can set

up the calculation as follows:

So, according to Fried’s Rule, the pediatric dosage appropriate for a

15-month-old would be 100 mg.

1. A child, 24 months old, needs acetaminophen, and the normal adult

dose is 650 mg. What is the appropriate dosage for the

child?________________

2. An 18-month-old needs amikacin sulfate, and the normal adult dose is

250 mg. What is the appropriate dosage for the child? ________________

3. A child, 30 months old, needs erythromycin, and the normal adult dose

is 250 mg QID. What is the appropriate dosage for the child?

Pediatric Dose = 100 mg

Pediatric Dose = 0.1 * 1000

Pediatric Dose =

Pediatric Dose =

15 (Age in months)

* 1000 mg (Adult Dose)

Chapter Five Dosage Calculations 17

FORMULA Pediatric Dosing

Fried’s Rule

Young’s Rule

Clark’s Rule

Child’s dosage =

Child’s weight in pounds

* Adult dosage

Child’s dosage =

Age of child in years

Age of child in years + 12

* Adult dosage

Child’s dosage =

Age in months

* Adult dosage

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

EXAMPLE 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 be

expressed 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 a

15-month-old would be 94 mg.

1. A 2-year-old child is prescribed amoxicillin, and the normal adult dose is

500 mg. What is the appropriate dosage for the child?________________

2. A 7-year-old needs propylthiouracil, and the normal adult daily dose is

150 mg. What is the appropriate dosage for the child?________________

3. A child, 10 years old, is prescribed Tavist® syrup, and the normal adult

dose is 1.34 mg BID. What is the appropriate dosage for the

child?________________

EXAMPLE 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 Example

5.5, set up the calculation, using Young’s Rule, as follows:

Pediatric Dose = 133 mg

Pediatric Dose = 0.133 * 1000

Pediatric Dose =

Pediatric Dose =

20 (Weight in pounds)

* 1000 mg (Adult Dose)

Pediatric Dose = 94 mg

Pediatric Dose = 0.094 * 1000

Pediatric Dose =

Pediatric Dose =

1.25 (Age in years)

13.25 (Age of child + 12)

* 1000 mg (Adult Dose)

18 Chapter Five Dosage Calculations

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

So, according to Clark’s Rule, the pediatric dosage, appropriate for a

15-month-old, weighing 20 pounds, would be 133 mg.

1. A child, weighing 85 pounds, is prescribed hydrochlorothiazide, and

the normal adult dose is 50 mg. What is the appropriate dosage for the

child?________________

2. A child, weighing 70 pounds, is prescribed quinine sulfate, and the

normal adult dose is 325 mg TID. What is the appropriate dosage for

the child?________________

3. A child, weighing 112 pounds, is prescribed Kaletra®, a protease

inhibitor combination therapy. The normal adult dose is 400 mg

lopinavir/100 mg ritonavir. What is the appropriate dosage for the

child?________________

Converting Pediatric Weight

To solve pediatric dosing calculations using the mg/kg method, you must

first determine the patient’s weight in kilograms. To convert weight in

pounds to kilograms, use the following formula:

Chapter Five Dosage Calculations 19

FORMULA Weight Conversion

1 kg = 2.2 lb

EXAMPLE 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 in

kilograms.

So 180 lb. equals 81.82 kg.

2.2 = 81.82 kg

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

Convert 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 Day

When the dose is stated in the manufacturer information as mg/kg/day, this

means we can calculate the patient’s weight in kilograms, multiply the recommended dose, and take into account the number of times per day the dose

is to be given. The goal is to determine how many milligrams can be given in

each dose.

Step 1: Determine weight in kilograms.

Step 2: Multiply by the recommended dose.

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

EXAMPLE 5.14 Using the infant from Example 5.9, determine the pediatric dosage

if it is recommended to administer 20 mg/kg/day (maximum of

1gm) of Streptomycin Sulfate.

The infant’s weight in kg has already been calculated as 9.09, so now we

will multiply the recommended number of milligrams by her weight in kilograms to calculate the appropriate daily pediatric dosage.

So, according to mg/kg/day, the patient should be given 181.8 mg of

Streptomycin 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

20 Chapter Five Dosage Calculations

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Using the patient from Example 5.13, an order is given for a dose stated

as 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 of

doses 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 a

child based on body weight in kilograms.

1. A dose of 4 mg/kg/day of Plaquenil® can be recommended for certain

children suffering from lupus. What would be the appropriate dosage

for a patient weighing 47 kg? ________________

2. The daily dose of Omnicef®, in children, is 14 mg/kg, up to a maximum

dose of 600 mg/day. What is the appropriate daily dosage for a patient

who 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 the

appropriate dosages for a child weighing 30 kg? ________________

4. A child, weighing 76 pounds, is prescribed the antibiotic, Cefaclor. It is

recommended for children to receive 20 mg/kg/day in divided doses

every 8 hours. How many mg should the child take per dose?

5. Acute lymphatic leukemia in children can respond well to methotrexate

given 2.5 mg/kg every 14 days by IV. What would be the appropriate

dosage of methotrexate to administer biweekly to a child weighing

110 pounds? ________________

Perform the following pediatric dosage calculations.

1. Rx tetracycline 25 mg/kg in four equal doses

Your 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

Chapter Five Dosage Calculations 21

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

2. Rx amoxicillin/potassium clavulanate 45 mg/kg/day q12h

Your patient is 6 years old and weighs 68 lb.

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

b. What is the total dosage per day? ________________

c. How much is each dose? ________________

3. Rx furosemide daily

Your patient is 3 years old and weighs 22 lb.

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

b. What is the daily dose? ________________

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

doses

Your patient is 5 years old and weighs 62 lb.

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

b. What is the total dosage per day? ________________

c. How much is each dose? ________________

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

per day

Your patient is 6 years old and weighs 54 lb.

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

b. What is the total dosage per day? ________________

c. How much is each dose? ________________

Dosage calculations are varied, and more than likely will be the pharmacy

calculations you perform most often. Dosage calculations include determining the number of doses, dispensing quantities, and ingredient quantities, for

both adult and pediatric patients.

1 mg>kg

22 Chapter Five Dosage Calculations

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

Chapter Five Dosage Calculations 23

1. 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 delivered

over 72 hours by one 0.075 mg/day

patch?________________

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 lidocaine 2%, qs to 200 mL. How much viscous

lidocaine 2% will you need to prepare the

order?________________

a. 60 mL c. 80 mL

b. 4 mL d. 200 mL

4. The recommended pediatric dose of ampicillin

is 25 mg/kg/day q8h. Your patient is a 4-weekold infant who weighs 8.7 pounds. Which is the

best 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 fumerate syrup 0.5 mg/5 mL last if the dose is tsp

daily?________________

a. 24 days c. 30 days

b. 48 days d. 60 days

6. How many grams of drug are in 480 mL of

docusate sodium syrup 60 mg/15 mL?

a. 28.8 g c. 1920 g

b. 1.92 g d. 2.88 g

7. How many milligrams are in a 2-mL dose of

prochlorperazine injection 5 mg/mL given IM

for severe nausea and vomiting?

a. 10 mg c. 2.5 mg

b. 5 mg d. 15 mg

8. How many milliliters of chloral hydrate syrup

500 mg/5 mL are required for a dose of

a. 2.5 mL c. 2 mL

b. 5 mL d. 1 mL

9. The recommended pediatric dose for promethazine is 0.25 mg/kg qid. What is the best

dose for a 12-year-old male who weighs

a. 2.5 mg c. 12.5 mg

b. 10 mg d. 15 mg

10. How many total grams of active ingredient are

in five syringes of testosterone 4 g/100 g topical

gel 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%

11. When solving dosage calculations, it is helpful

to look for the given. ________________

a. true b. false

12. When setting up ratios and proportions to solve

dosage calculations, it is best to keep like units

consistent. ________________

a. true b. false

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

24 Chapter Five Dosage Calculations

13. The unknown, x, will always be located in the

upper left corner when setting up dosage

calculations. ________________

a. true b. false

14. When choosing the answer in a multiple-choice

question, you should find the numerical answer

regardless of units. ________________

a. true b. false

15. You can solve most dosage calculations by

cross-multiplying. ________________

a. true b. false

16. Describe why proper dosing of medications is

important 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 of

a cream that is 4 mg/mL? ________________

20. How many milliliters will be required to provide the necessary dose of albuterol oral syrup

2 mg/5 mL to be given 0.2 mg/kg/day tid for a

patient who weighs 88 lb.? ________________

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

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