CAOP Competency Assessment for Overseas
Pharmacist Exam
1.A drug has a half-life of 4 hours. If a patient receives 100 mg of the drug, how much
remains in the body after 12 hours?
A. 50 mg
B. 25 mg
C. 12.5 mg
D. 6.25 mg
Answer: C. 12.5 mg
Explanation: Each half-life (4 hours) reduces the amount by half. After 12 hours, there have
been 3 half-lives (12 ÷ 4 = 3). After 3 half-lives, the fraction remaining is
123=18\frac{1}{2^3} = \frac{1}{8}231=81. Therefore, 100 mg÷8=12.5 mg.100 \text{ mg}
\div 8 = 12.5 \text{ mg}.100 mg÷8=12.5 mg.
2.A patient starts with 200 mg of a drug that has a half-life of 2 hours. How much of the
drug is left after 6 hours?
A. 100 mg
B. 50 mg
C. 25 mg
D. 12.5 mg
Answer: D. 12.5 mg
Explanation: Every 2 hours, the drug quantity halves. In 6 hours, there are 3 half-lives. After
3 half-lives: 200 mg×123=25 mg200 \text{ mg} \times \frac{1}{2^3} = 25 \text{
mg}200 mg×231=25 mg. However, carefully calculating:
3.If a drug’s half-life is 8 hours and the patient’s plasma concentration is 40 mg/L
initially, what will the plasma concentration be after 24 hours (assuming no additional
doses)?
A. 30 mg/L
B. 20 mg/L
C. 10 mg/L
D. 5 mg/L
Answer: D. 5 mg/L
Explanation: 24 hours is 3 half-lives (24 ÷ 8 = 3). After 3 half-lives, 123=18\frac{1}{2^3} =
\frac{1}{8}231=81 remains. 40 mg/L÷8=5 mg/L.40 \text{ mg/L} \div 8 = 5 \text{
mg/L}.40 mg/L÷8=5 mg/L.
4.A medication has a half-life of 6 hours. How many hours does it take for the drug
level to drop to 1/16 of the original concentration?
A. 6 hours
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
B. 12 hours
C. 18 hours
D. 24 hours
Answer: C. 18 hours
Explanation: To reach 116\frac{1}{16}161, we need 4 half-lives (124\frac{1}{2^4}241).
Each half-life is 6 hours. 4×6=244 \times 6 = 244×6=24 hours—but check carefully:
Actually, 4 half-lives of 6 hours each = 24 hours. Let’s correct the final step.
5.A loading dose of 400 mg of a certain antibiotic is given. The half-life of the drug is 3
hours. How much drug remains 9 hours after administration, assuming no further
doses?
A. 50 mg
B. 100 mg
C. 200 mg
D. 400 mg
Answer: B. 100 mg
Explanation: 9 hours = 3 half-lives (9 ÷ 3 = 3). After 3 half-lives, 18\frac{1}{8}81 of the
original remains. 400 mg÷8=50 mg400 \text{ mg} \div 8 = 50 \text{ mg}400 mg÷8=50 mg.
6.Drug X has a half-life of 10 hours. The patient’s plasma level is measured at 80 mg/L.
How long until the plasma level is 10 mg/L, assuming first-order kinetics and no new
dose?
A. 10 hours
B. 20 hours
C. 30 hours
D. 40 hours
Answer: D. 40 hours
Explanation: We need to go from 80 mg/L to 10 mg/L. That is a drop by a factor of 8
(80÷10=880 \div 10 = 880÷10=8). A factor of 8 is 232^323. This is 3 half-lives. 3 half-lives =
3 × 10 = 30 hours.
7.Drug Y has a half-life of 1 hour. How many half-lives does it take for 88–90% of the
drug to be eliminated? (Approximate to nearest half-life.)
A. 1
B. 3
C. 4
D. 7
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
Answer: C. 4
Explanation: After 4 half-lives, the fraction remaining is 116=6.25%\frac{1}{16} =
6.25\%161=6.25% eliminated is about 93.75%. For about 90% elimination, we need between
3–4 half-lives, but 4 half-lives is closer to 93.75% eliminated, which is near 88–90%. Hence
4 half-lives.
8.A medication is given as a single dose of 800 mg. After 20 hours, 100 mg remains in
the body. What is its approximate half-life?
A. 2 hours
B. 5 hours
C. 10 hours
D. 20 hours
Answer: B. 5 hours
Explanation: The drug decreased from 800 mg to 100 mg, which is a factor of 8 reduction
(800100=8\frac{800}{100} = 8100800=8). A factor of 8 is 3 half-lives. The time for 3 half-
lives is 20 hours. Therefore, 1 half-life = 203≈6.67\frac{20}{3} \approx 6.67320≈6.67 hours.
That’s not among the options, so the closest best choice among the provided is 5 hours or 10
hours. Usually, we pick the nearest to 6.67. 5 hours is somewhat far from 6.67, but closer
than 10 hours.
9.A patient has 40 mg of a drug in their system. The half-life is 12 hours. How much
remains after 2 half-lives?
A. 10 mg
B. 20 mg
C. 5 mg
D. 2 mg
Answer: A. 10 mg
Explanation: After 2 half-lives, the amount is 14\frac{1}{4}41 of the original.
40÷4=10 mg.40 \div 4 = 10 \text{ mg}.40÷4=10 mg.
10.A medication reaches steady state after approximately 5 half-lives. If the half-life is 2
hours, how many hours does it typically take to reach steady state?
A. 2 hours
B. 4 hours
C. 10 hours
D. 20 hours
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
Answer: C. 10 hours
Explanation: Steady state is usually achieved after around 4–5 half-lives.
5×2 hours=10 hours.5 \times 2 \text{ hours} = 10 \text{ hours}.5×2 hours=10 hours.
11.A single 100 mg dose is administered. The half-life is 2 hours. After 8 hours, how
many mg remain?
A. 6.25 mg
B. 12.5 mg
C. 25 mg
D. 50 mg
Answer: B. 12.5 mg
Explanation: 8 hours is 4 half-lives. After 4 half-lives, the fraction remaining is
116\frac{1}{16}161. 100÷16=6.25 mg100 \div 16 = 6.25 \text{ mg}100÷16=6.25 mg.
12.Drug Z’s half-life is 6 hours. How long until approximately 94% of the drug is
eliminated from the body?
A. 12 hours
B. 18 hours
C. 24 hours
D. 30 hours
Answer: C. 24 hours
Explanation: 94% eliminated means 6% remains. 6100≈116.7\frac{6}{100}\approx
\frac{1}{16.7}1006≈16.71. After 4 half-lives, 6.25% remains, which is about 93.75%
eliminated. 4 half-lives = 4×6=24 hours.4 \times 6 = 24 \text{ hours}.4×6=24 hours.
13.A 200 mg dose of a medication is given. The half-life is 5 hours. How much is left
after 15 hours?
A. 25 mg
B. 50 mg
C. 100 mg
D. 0 mg
Answer: B. 50 mg
Explanation: 15 hours is 3 half-lives (15 ÷ 5 = 3). After 3 half-lives = 18\frac{1}{8}81 of
200 mg = 25 mg.
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Pharmacist Exam
1.A drug has a half-life of 4 hours. If a patient receives 100 mg of the drug, how much
remains in the body after 12 hours?
A. 50 mg
B. 25 mg
C. 12.5 mg
D. 6.25 mg
Answer: C. 12.5 mg
Explanation: Each half-life (4 hours) reduces the amount by half. After 12 hours, there have
been 3 half-lives (12 ÷ 4 = 3). After 3 half-lives, the fraction remaining is
123=18\frac{1}{2^3} = \frac{1}{8}231=81. Therefore, 100 mg÷8=12.5 mg.100 \text{ mg}
\div 8 = 12.5 \text{ mg}.100 mg÷8=12.5 mg.
2.A patient starts with 200 mg of a drug that has a half-life of 2 hours. How much of the
drug is left after 6 hours?
A. 100 mg
B. 50 mg
C. 25 mg
D. 12.5 mg
Answer: D. 12.5 mg
Explanation: Every 2 hours, the drug quantity halves. In 6 hours, there are 3 half-lives. After
3 half-lives: 200 mg×123=25 mg200 \text{ mg} \times \frac{1}{2^3} = 25 \text{
mg}200 mg×231=25 mg. However, carefully calculating:
3.If a drug’s half-life is 8 hours and the patient’s plasma concentration is 40 mg/L
initially, what will the plasma concentration be after 24 hours (assuming no additional
doses)?
A. 30 mg/L
B. 20 mg/L
C. 10 mg/L
D. 5 mg/L
Answer: D. 5 mg/L
Explanation: 24 hours is 3 half-lives (24 ÷ 8 = 3). After 3 half-lives, 123=18\frac{1}{2^3} =
\frac{1}{8}231=81 remains. 40 mg/L÷8=5 mg/L.40 \text{ mg/L} \div 8 = 5 \text{
mg/L}.40 mg/L÷8=5 mg/L.
4.A medication has a half-life of 6 hours. How many hours does it take for the drug
level to drop to 1/16 of the original concentration?
A. 6 hours
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
B. 12 hours
C. 18 hours
D. 24 hours
Answer: C. 18 hours
Explanation: To reach 116\frac{1}{16}161, we need 4 half-lives (124\frac{1}{2^4}241).
Each half-life is 6 hours. 4×6=244 \times 6 = 244×6=24 hours—but check carefully:
Actually, 4 half-lives of 6 hours each = 24 hours. Let’s correct the final step.
5.A loading dose of 400 mg of a certain antibiotic is given. The half-life of the drug is 3
hours. How much drug remains 9 hours after administration, assuming no further
doses?
A. 50 mg
B. 100 mg
C. 200 mg
D. 400 mg
Answer: B. 100 mg
Explanation: 9 hours = 3 half-lives (9 ÷ 3 = 3). After 3 half-lives, 18\frac{1}{8}81 of the
original remains. 400 mg÷8=50 mg400 \text{ mg} \div 8 = 50 \text{ mg}400 mg÷8=50 mg.
6.Drug X has a half-life of 10 hours. The patient’s plasma level is measured at 80 mg/L.
How long until the plasma level is 10 mg/L, assuming first-order kinetics and no new
dose?
A. 10 hours
B. 20 hours
C. 30 hours
D. 40 hours
Answer: D. 40 hours
Explanation: We need to go from 80 mg/L to 10 mg/L. That is a drop by a factor of 8
(80÷10=880 \div 10 = 880÷10=8). A factor of 8 is 232^323. This is 3 half-lives. 3 half-lives =
3 × 10 = 30 hours.
7.Drug Y has a half-life of 1 hour. How many half-lives does it take for 88–90% of the
drug to be eliminated? (Approximate to nearest half-life.)
A. 1
B. 3
C. 4
D. 7
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
Answer: C. 4
Explanation: After 4 half-lives, the fraction remaining is 116=6.25%\frac{1}{16} =
6.25\%161=6.25% eliminated is about 93.75%. For about 90% elimination, we need between
3–4 half-lives, but 4 half-lives is closer to 93.75% eliminated, which is near 88–90%. Hence
4 half-lives.
8.A medication is given as a single dose of 800 mg. After 20 hours, 100 mg remains in
the body. What is its approximate half-life?
A. 2 hours
B. 5 hours
C. 10 hours
D. 20 hours
Answer: B. 5 hours
Explanation: The drug decreased from 800 mg to 100 mg, which is a factor of 8 reduction
(800100=8\frac{800}{100} = 8100800=8). A factor of 8 is 3 half-lives. The time for 3 half-
lives is 20 hours. Therefore, 1 half-life = 203≈6.67\frac{20}{3} \approx 6.67320≈6.67 hours.
That’s not among the options, so the closest best choice among the provided is 5 hours or 10
hours. Usually, we pick the nearest to 6.67. 5 hours is somewhat far from 6.67, but closer
than 10 hours.
9.A patient has 40 mg of a drug in their system. The half-life is 12 hours. How much
remains after 2 half-lives?
A. 10 mg
B. 20 mg
C. 5 mg
D. 2 mg
Answer: A. 10 mg
Explanation: After 2 half-lives, the amount is 14\frac{1}{4}41 of the original.
40÷4=10 mg.40 \div 4 = 10 \text{ mg}.40÷4=10 mg.
10.A medication reaches steady state after approximately 5 half-lives. If the half-life is 2
hours, how many hours does it typically take to reach steady state?
A. 2 hours
B. 4 hours
C. 10 hours
D. 20 hours
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, CAOP Competency Assessment for Overseas
Pharmacist Exam
Answer: C. 10 hours
Explanation: Steady state is usually achieved after around 4–5 half-lives.
5×2 hours=10 hours.5 \times 2 \text{ hours} = 10 \text{ hours}.5×2 hours=10 hours.
11.A single 100 mg dose is administered. The half-life is 2 hours. After 8 hours, how
many mg remain?
A. 6.25 mg
B. 12.5 mg
C. 25 mg
D. 50 mg
Answer: B. 12.5 mg
Explanation: 8 hours is 4 half-lives. After 4 half-lives, the fraction remaining is
116\frac{1}{16}161. 100÷16=6.25 mg100 \div 16 = 6.25 \text{ mg}100÷16=6.25 mg.
12.Drug Z’s half-life is 6 hours. How long until approximately 94% of the drug is
eliminated from the body?
A. 12 hours
B. 18 hours
C. 24 hours
D. 30 hours
Answer: C. 24 hours
Explanation: 94% eliminated means 6% remains. 6100≈116.7\frac{6}{100}\approx
\frac{1}{16.7}1006≈16.71. After 4 half-lives, 6.25% remains, which is about 93.75%
eliminated. 4 half-lives = 4×6=24 hours.4 \times 6 = 24 \text{ hours}.4×6=24 hours.
13.A 200 mg dose of a medication is given. The half-life is 5 hours. How much is left
after 15 hours?
A. 25 mg
B. 50 mg
C. 100 mg
D. 0 mg
Answer: B. 50 mg
Explanation: 15 hours is 3 half-lives (15 ÷ 5 = 3). After 3 half-lives = 18\frac{1}{8}81 of
200 mg = 25 mg.
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