NAPLEX PRACTICE QUESTIONS2 1 ca l cu l a t i on  ques t i on s t o

p repa re f o r t he boa rd exams  

RxCa l cu l a t i ons

MICHAEL DANQUAH , MS , PHD

C O N T E N T S

0 3

08

1 0

1 5

1 7

2 2

2 5

2 8

3 2

 

CONVERS IONS

TOTA L PARENTERA L NUTR I T I ON

CONCENTRAT ION

PH AND BUF FERS

M I L L I EQU I VA L ENTS

OSMOLAR I T Y    

RECONST I TU T ION

F LOW RATE CA LCU LA T IONS

ANSWERS

N A P L E X P R A C T I C E Q U E S T I O N S

C O N V E R S I O N S

LEARN  YOUR CONVERSION FACTORS AND

PRACTICE HOW TO USE THEM

PAGE  3

QUESTION 1

How many milligrams

are equal to 1/150 gr of

Nitroglycerine?

PAGE 4

R E V I EW HOW T O CONV ER T F ROM

GRA I N T O M I L L I G R AM

QUESTION 2

How many grams of

Heparin are required

to prepare 1 quart of

0.45% solution?

PAGE 5

R E V I EW HOW T O   CONV ER T F ROM

QUAR T T O M I L L I L I T E R S

QUESTION 3

If I want to make a

gallon of cough

preparation that will

contain 1 grain of

active ingredient per

teaspoonful. How

many grams of active

ingredient will I need?

PAGE 6

R E V I EW HOW T O   CONV ER T   F ROM

GRA I N T O GRAMS AND GA L L ON S T O

L I T E R S

QUESTION 4

If a prescription reads

“Augmentin 875 mg po

bid x 10 days,” how

many mL of

Augmentin 250 mg/5

mL are required to fill a

ten-day supply?

PAGE  7

R E V I EW HOW T O SO L V E A DA Y S

S U P P L Y T Y P E P ROB L EM  

T O T A L P A R E N T E R A L

N U T R I T I O N

PRACTICE USING CONVERSION FACTORS

AND  EQUATIONS FOR TPN CALCULATIONS

PAGE 8

QUESTION 5

JM is a patient in the ICU

(6'1" and 256 pounds). He is

currently receiving 3-in-1

PN at 125 mL/h. The PN is

12.1% w/v dextrose and

4.7%w/v protein. The

prescriber wants the

patient's protein intake

from the PN to be 1.4 g/kg

IBW per day. By how many

grams will the current

protein need to be reduced

to achieve this?

PAGE  9

R E V I EW HOW T O SO L V E A   T PN   T Y P E

P ROB L EM  

C O N C E N T R A T I O N

REVIEW THE VARIOUS WAYS OF

EXPRESSICONVERSION FACTORS

AND  EQUATIONS FOR TPN CALCULATIONS

PAGE 10

QUESTION 6

If 60 g of 1%

hydrocortisone are

mixed with 80 g of

2.5% hydrocortisone,

what is the

percent of

hydrocortisone in the

final mixture?

PAGE  11

R E V I EW HOW T O SO L V E F OR F I N A L

CONC EN T RA T I ON O F A P R E PARA T I ON

G I V EN T H E CONC EN T RA T I ON AND

QUAN T I T I E S O F COMPONEN T S T O B E

COMB I N ED

QUESTION 7

How many mL of 75%

alcohol should be

mixed with 10%

alcohol to prepare 30%

of 500 mL alcohol

solution ?

PAGE  12

R E V I EW HOW T O SO L V E F OR F I N A L

CONC EN T RA T I ON O F A P R E PARA T I ON

G I V EN T H E CONC EN T RA T I ON AND

QUAN T I T I E S O F COMPONEN T S T O B E

COMB I N ED

QUESTION 8

An ointment contains

1%w/w calamine. How

much calamine

powder would be

appropriate to add to a

200g of the ointment

to produce a 4% w/w

calamine ointment?

PAGE  13

HOW T O SO L V E A D I L U T I ON S AND

CONC EN T RA T I ON QUE S T I ON U S I N G

T H E A L L I G A T I ON ME THOD

QUESTION 9

How much Lidocaine is

required to prepare 30

mL of a 1:1000

Lidocaine solution?

PAGE  14

HOW T O SO L V E A RA T I O S T R ENG TH

CA L CU L A T I ON S P ROB L EM

P H A N D B U F F E R S

PRACTICE KEY CONCEPTS IN PH AND

BUFFER CALCULATIONS

PAGE 15

QUESTION 10

What is the ratio of

ionized to unionized

species of a weakly

acidic drug at pH = 7 if

the pKa = 5?

PAGE  16

HOW T O SO L V E A PH AND BU F F E R

CA L CU L A T I ON S P ROB L EM U S I N G T H E

HENDER SON - HA S S E L B A L CH EQUA T I ON

M I L L I E Q U I V A L E N T S

PRACTICE USING KEY EQUATIONS

IN  MILLIEQUIVALENTS  CALCULATIONS

PAGE 17

QUESTION 11

How many mEqs of K+

are present in 750 mg

of a KCl capsule? [ K+ =

39, Cl- = 35.5]

PAGE  18

HOW T O SO L V E F OR

M I L L I E QU I V A L EN T S O F AN I O N G I V EN

T H E MAS S AND MOL E CU L AR WE I GH T

QUESTION  12

How many grams of

CaCl2 are required to

prepare a 1 gallon

solution that contains

20 mEq of calcium

ions? [mw CaCl2 =

111g/mol]

PAGE  19

HOW T O SO L V E F OR T H E QUAN T I T Y O F

A S A L T NE ED ED T O S U P P L Y A G I V EN

M I L L I E QU I V A L EN T O F AN I O N

QUESTION 13

If a prescription calls to

dispense 8 fl oz of KCl

in such a way that 1

teaspoonful of solution

contains 0.5 mEqs of

drug, how many grams

of KCl are required to

prepare the above

prescription? [mw of

KCl = 74.5g/mol]

PAGE  20

HOW T O SO L V E F OR T H E QUAN T I T Y O F

A S A L T NE ED ED T O S U P P L Y A G I V EN

M I L L I E QU I V A L EN T O F AN I O N

QUESTION 14

You receive a prescription

for 240 mL of a potassium

citrate solution with a

concentration of 15

mEq/15mL. How much

potassium citrate must

you weigh out to

compound this

prescription? (MW of

C6H5K3O7 = 306)

PAGE  21

HOW T O SO L V E F OR T H E QUAN T I T Y O F

A S A L T NE ED ED T O S U P P L Y A G I V EN

M I L L I E QU I V A L EN T O F AN I O N G I V EN

T H E CONC EN T RA T I ON O F T H E

SO L U T I ON

O S M O L A R I T Y  

PRACTICE USING KEY EQUATIONS

IN  OSMOLARITY CALCULATIONS

PAGE  22

QUESTION  15

How many mOsmols/L

are represented by

1000 mL 0.9% sodium

chloride solution?

PAGE  23

HOW T O CA L CU L A T E OSMO LAR I T Y

G I V EN T H E CONC EN T RA T I ON O F T H E

SO L U T I ON

QUESTION  16

How many mOsmols/L

are represented by a

50 mL 8.4% sodium

bicarbonate solution?

[mw = 84 g/mol]

PAGE  24

HOW T O CA L CU L A T E OSMO LAR I T Y

G I V EN T H E CONC EN T RA T I ON O F T H E

SO L U T I ON

R E C O N S T I T U T I O N

PRACTICE KEY  CONCEPTS IN

RECONSTITUTION  CALCULATIONS

PAGE  25

QUESTION  17

A patient is ordered a 130

mg dose of a drug in 50

mL of D5W. A vial

contains 1 gram of the

powdered drug. The drug

has a powder volume of

0.4 mL. How many

milliliters will be needed

to fill the patient order if

the concentration after

reconstitutions is 250

mg/mL? 

PAGE  26

HOW T O CA L CU L A T E T H E VO LUME O F A

R E CON S T I T U T ED SO L U T I ON NE ED ED T O

F I L L A PA T I E N T S ORDER

QUESTION  18

Your bottle of Amoxil

(amoxicillin) says to

add 39 mL to the bottle

to get a solution of 150

mg/tsp. The total

amount in the bottle is

2 g. What is the

powder volume?

PAGE  27

HOW T O CA L CU L A T E POWDER VO LUME

F L O W R A T E S

PRACTICE KEY  CONCEPTS IN  FLOW

RATE  CALCULATIONS

PAGE  28

QUESTION  19

Four grams of

Levofloxacin (mixed

with 500 mL 0.9%

NaCl) is administered

via slow I.V. infusion

over 24 hours. If the I.V.

set delivers 10

drops/ml, what would

be the rate of flow in

drops/ min?

PAGE  29

HOW T O DE T E RM I N E F L OW RA T E I N

DROP S P E R M INU T E

QUESTION 20

A 60-kg patient is to

receive a constant

infusion of dobutamine

at a rate of 5

mcg/kg/min. The

available solution has a

concentration of 0.5

mg/mL. For what rate

should the infusion

pump be set?

PAGE  30

HOW T O DE T E RM I N E F L OW RA T E O F AN

I N F U S I ON PUMP I N M I L L I L I T E R S P E R

HOUR

QUESTION  21

A patient is receiving an

IV 1000 cc per 8 hour.

When 600 mL have been

run in from the 1-L bag,

the physician ordered the

remainder to be infused

over the next 6 hours. The

IV set is calibrated at 10

gtt/mL. What is the new

flow rate in drops per

minute? 

PAGE  31

HOW T O DE T E RM I N E F L OW RA T E I N

DROP S P E R M INU T E

ANSWERS

1. 0.432 mg

2. 4.26 g

3. 49 g

4. 350 mL

5. 29.14 g

6. 3.5 drops/min

7. 153.85 mL

8. 6.25 g

9. 30 mg

10. 100:1

11. 10 mEq

PAGE  32

12. 1.11 g

13. 1.788 g

14. 24.48 g

15. 307.7 mOsm/L

16. 2000 mOsm/L

17. 0.52 mL

18. 27.67 mL

19. 3.5 drops/min

20. 36 mL/h

21. 11.1 drops/min

 

G E T M O R E N A P L E X

P R A C T I C E Q U E S T I O N S

T O D A Y  

L E A R N M O R E