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# PEBC Calculations With Solutions

87. A solution contains 5% of anhydrous dextrose in water for injection. How many milliosmoles per liter are

represented by this concentration? (MW of dextrose is 180 g). Question could be read: What is the osmolarity of

D5W?

a. 255.50 mOsmol/L.

b. 278.00 mOsmol/L.*

c. 287.00 mOsmol/L.

d. 301.30 mOsmol/L.

e. 310.00 mOsmol/L.

88. A solution contains 156 mg of K+

ions per 100 ml. How many milliosmoles are represented in a liter of the

solution? (MW of K+

= 39 g)

a. 30 mOsmol/L.

b. 35 mOsmol/L.

c. 40 mOsmol/L.*

d. 45 mOsmol/L.

e. 50 mOsmol/L.

89. A solution contains 10 mg% of Ca++ ions. How many milliosmoles are represented in 1 liter of the solution?

(MW of Ca++ = 40 g).

a. 0.5 mOsmol/L.

b. 1.0 mOsmol/L.

c. 1.5 mOsmol/L.

d. 2.0 mOsmol/L.

e. 2.5 mOsmol/L.*

90. How many milliosmoles are represented in a liter of an 0.9% sodium chloride solution? (MW of Nacl = 58.5,

species = 2).

a. 308 mOsmol/L.*

b. 358 mOsmol/L.

c. 399 mOsmol/L.

d. 413 mOsmol/L.

e. 429 mOsmol/L.

91. A ready-to-use enteral nutritional solution has an osmolarity of 470 mOsm/L. How many ml of purified water are

needed to adjust 8 fluid ounces of the enteral solution to an osmolarity (280 mOsm/L)?

a. 120 ml.

b. 160 ml.*

c. 240 ml.

d. 300 ml.

e. 400 ml.

One of the most convenient methods of solving this problem is using the equation:

(Q1) (C1) = (Q2) (C2)

5 g of dextrose are found in 100 ml of water

x g of dextrose are found in 1000 ml (L) of water.

Osmolarity = ( )

( / ) 1000

MolecularWeight g

Weight g L xSpeciesx

= 180

50x1x1000 = 277.8 mOsmol/L

156 mg of K+

are found in 100 ml of water

x g of K+ are found in 1000 ml (L) of water, x = 1560 mg = 1.56 g

Osmolarity = ( )

( / ) 1000

MolecularWeight g

Weight g L xSpeciesx

= 39

1.56x1x1000 = 40 mOsmol/L

10 mg of Ca++ are found in 100 ml of water

x g of Ca++ are found in 1000 ml (L) of water, x = 100 mg = 0.1 g

Osmolarity = ( )

( / ) 1000

MolecularWeight g

Weight g L xSpeciesx

= 40

0.1x1x1000 = 2.5 mOsmol/L

0.9 mg of Nacl is found in 100 ml of water

x g of Nacl are found in 1000 ml (L) of water, x = 9 g

Osmolarity = ( )

( / ) 1000

MolecularWeight g

Weight g L xSpeciesx

= 58.5

9x2x1000 = 307.7 mOsmol/L

Page 23 of 24

d. 3000 days.*

77.

78. Approximately 50% of the drug is excreted unchanged in the urine. If the normal dosage scheduled for

Dicloxacillin is 125mg every 6 hours. A patient with renal function 20% of the normal should receive?

a. 25mg q6h.

b. 31.25mg q6h.

c. 75mg q6h.*

d. 62.5mg q6h.

79.

80. What is the minimum quantity that can be weighed on a balance with a sensitivity requirement of 6 mg if an error

of 5% is permissible?

a. 100 mg.

b. 120 mg.*

c. 140 mg.

d. 160 mg.

Sensitivity Requirement (SR) = Minimum Qty to be weighed x Permissible error %

SR = (x) mg x 5% 6 mg = (x) mg x 5/100 (x) mg = 100 x 6/5 = 120 mg

81.

82. If the pka of Aspirin is 6.4, what fraction of the drug would be ionized at pH 7.4?

a. 60%

b. 75%

c. 80%

d. 90%*

e. 100%

83. If half life elimination of a drug is 2 hours, what fraction of the original dose of the drug will remain in the body

after 4 hours?

a. 80%

b. 50%

c. 25%*

d. 12.5%

e. 7.5%

84. A graph (log Cp versus time) of Cp = CO e-kt will give: (Cp = concentration of drug, Dose = e-kt)

a. A straight line with a positive slope.

b. A straight line with a negative slope.*

c. Does not exist.

d. A circle.

e. Negative slope.

85. A pharmacist adds one gram of calcium chloride (CaCl2. 2H2O) to a 500 ml bottle of water. How many mEq. Of

chloride are present in each ml of solution? (Ca = 40; MW CaCl2 = 111; H2O = 18).

a. 0.014

b. 0.027

c. 0.036

d. 0.041

e. 13.60*

86. Suppose 12 suppositories, each containing 300 mg aspirin, are required. Given the density factor of aspirin is 1.1,

what is the amount of Cocoa butter required for the preparation?

a. 20.40 g.

b. 20.04 g.

c. 20.54 g

d. 20.73 g.*

e. 18.22 g.

% of ionized drug = arg ( ) 1 10

100 ch e PH − pKa +

= 1(7.4 6.4) 1 10

100

− − + = 1(1) 1 10

100− + = 1 1 10

100− + = 1.1

100

1 (0.1)

100 = + =

Charge:

Acid = -1

Base = 1

10-1=0.1

10-2=0.01

10-3-0.001

10-4=0.0001

Total amount of aspirin = 12 x 300 = 3,600 mg = 3.6 g.

Amount of aspirin replacing Cocoa butter = DensityFactorofAspirin

TotalAmountOfAspirin = 1.1

3.6 = 3.27

Total amount of Cocoa Butter = 12 x 2 = 24 g.

Amount of Cocoa Butter Needed = 24 – 3.27 = 20.73 g

Page 22 of 24

66.

67. What is the Creatinine clearance (ClCR) of a 20 year old man weighing 72 kg and has a Serum Creatinine

Concentration (CCR)=1.0 mg/dl?

a. 140 ml/min.

b. 120 ml/min.*

c. 100 ml/min.

d. 80 ml/min.

By applying the method of Cockroft and Gault

ClCR = 72( . . / )

(140 , , )( . . . )

Ccr in mg dl

− age in years body weight in kg

ClCR = 72(1)

(140 − 20)(72)

= 120 ml/min

68.

69. 500,000 unit of penicillin G is equal to: (1 unit = 0.6 mcg)

a. 200 mg.

b. 300 mg.*

c. 400 mg.

d. 600 mg.

70.

71. The press coating of a tablet contains 200 mg of a drug for immediate release. The amount of the drug will

provide an adequate therapeutic level. The drug in the slow release core must sustain therapeutic level for 12

hours. If the elimination rate constant of this drug is 0.15 hr-1, the total amount of drug in each tablet is:

a. 360 mg.

b. 460 mg.

c. 560 mg.*

d. 660 mg.

72.

73. In an adequately powered, randomized controlled trial conducted over 2 years, the desired clinical outcome (i.e.

prevention of a serious cardiovascular event) with a new drug is achieved in 25% of the study sample. In the

patients who receive a placebo, only 15% obtain the same clinical benefit. The relative risk reduction achieved

with the new drug over the study period is:

a. 10%.

b. 15%.

c. 25%.

d. 40%*.

e. 50%.

Divide (15%/25%)x100= 60 then take 60 off 100, 100-60=40%

74. In adequately powered, randomized controlled trial conducted over 3 years, a specific serious side effect (i.e.

reduction in leukocytes) with conventional therapy is seen in 0.5% of the study sample. In patients who receive a

newly discovered drug, only 0.45% experience the same side effect. Based on these results, the minimum number

of patients that would have to receive the new drug for 3 years to statistically demonstrate the prevention of one

episode of this side effect in at least one patient is:

a. 15.

b. 20.

c. 150.

d. 200.

e. 2000*.

Subtract (0.5%-0.45%)x100=0.05, then divide 100/0.0.5=2000.

75.

76. A drug degrades at the rate of 1mg in 60 day from 100mg, what is the t1/2 of the drug?

a. 6000 days.

b. 5000 days.

c. 4000 days.

Page 21 of 24

61. The concentration of sodium fluoride (NaF) in a community’s drinking water is 0.6 ppm. Express this

concentration as a percentage.

a. 0.00006%.

b. 0.0006%.

c. 0.006%.

d. 0.06%

e. 0.6%

Sodium fluoride is a solid chemical. The o.6 ppm concentration indicates 0.6 g of sodium fluoride present in

1,000,000 ml of solution. Therefore, the grams present in 100 ml will be:

ml

x

1,000,000ml 100

0.6 = then g

o x

x 0.00006

1,000,000

.6 100 = =

62. The upper therapeutic drug concentration for valproic acid is considered to be 100 μg / ml . Express this value in

terms of mg/dL.

a. 0.1 mg/dL.

b. 1 mg/dL.

c. 10 mg/dL.

d. 100 mg/dL.

e. 1000 mg/dL.

Because 1000 μg = 1 mg and 100 ml = 1 dL.

100 μg = 0.1 mg/ml = 10 mg/dL

63. The USP contains nomograms for estimating body surface area (BSA) for both children and adults. Which of the

following measurements must be known in order to use this nomogram?

a. Age and height.

b. Age and weight.

c. Height and Creatinine clearance.

d. Height and weight.

e. Weight and sex.

The nomogram in the USP consists of three parallel vertical lines. The left line is calibrated with height

measurements in both centimeters and inches, whereas the right line lists weights in kilograms and pounds. Using

data based on the patient’s measurements, a line is drawn between the two outside parallel lines. The intercept on

the middle line, which is calibrated in square meters of body surface area, allows the estimation of the patient’s

BSA.

64. What is the minimum amount of a potent drug that may be weighted on a prescription balance with a sensitivity

requirement of 6 mg if at least 98% accuracy is required?

a. 6 mg.

b. 120 mg.

c. 180 mg.

d. 200 mg.

e. 300 mg.

Sensitivity Requirement (SR) = (Minimum weighable amount) x (acceptable error)

Minimum weighable amount = (6)/2% = 300 mg.

65. A total parentral nutrition (TPN) order requires 500 ml of D30W. How many ml of D40W should be used if the

D30W is not available?

a. 125 ml.

b. 300 ml.

c. 375 ml.

d. 400 ml.

e. 667 ml.

500 ml of D30W will contain 150 g of dextrose. D40W contains 40 g of dextrose per 100 ml.

ml x

g 150

100

40 = Then ml x

x 375

40

150 100 = =

Page 20 of 24

5860 mg = (x) (74.6)/1 = 78.5 mg

58. Lanoxin pediatric elixir contains 0.05 mg of digoxin per ml. How many micrograms are there in 3 ml of the

elixir?

a. O.15 μg .

b. 0.015 μg .

c. 1.5 μg .

d. 0.0015 μg .

e. None of the above.

1 mg = 1000 μg . Therefore, 0.15 mg of digoxin contained in 3 ml of the elixir would be equivalent to 150 μg of

drug.

59. How many ml of adrenaline chloride solution (0.1%) may be used to prepare the solution.

a. 0.002 ml.

b. 0.04 ml.

c. 1 ml.

d. 2 ml.

e. 5 ml.

Use the equation of: (Q1) (C1) = (Q2) (C2)

(4 ml) (1/2000) = (x ml) (1/1000) then x = 2 ml.

60. Five thousand (5000) nanogram equals 5:

a. Centigrams.

b. Grams.

c. Kilogram.

d. Microgram.

e. Milligram.