Pharmaceutical calculations

50 Gulf Prometric Pharmacist (DHA, DOH, MOH, SCFHS, QCHP) practice questions on Pharmaceutical calculations, part of Pharmaceutics, Pharmacokinetics and Calculations. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Calcium gluconate (MW 430) 1 g is given for hypocalcaemia. Approximately how many mEq of calcium does it provide?
1. A4.7 mEq
2. B9.3 mEq
3. C1.0 mEq
4. D2.3 mEq
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Answer: A · 4.7 mEq
1,000 mg / 430 = 2.33 mmol. Calcium is divalent, so mEq = 2.33 x 2 = 4.65, or about 4.7 mEq.
- B: 9.3 doubles the valence twice.
- C: 1.0 does not follow from the calculation.
- D: 2.3 is the mmol value without the valence.
Remember this
mEq = (mg / MW) x valence; calcium gluconate 1 g is about 4.7 mEq calcium.
Question 2 · Medium
A patient is 170 cm tall and weighs 70 kg. What is the body surface area by the Mosteller formula, sqrt(height in cm x weight in kg / 3,600)?
1. A2.10 m2
2. B1.91 m2
3. C1.65 m2
4. D1.82 m2
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Answer: D · 1.82 m2
BSA = sqrt(170 x 70 / 3,600) = sqrt(3.306) = 1.82 m2. The result of the square root must be taken before reporting.
- A: 2.10 m2 is too high for this height and weight.
- B: 1.91 m2 does not match the calculation.
- C: 1.65 m2 is too low for this height and weight.
Remember this
Mosteller BSA = square root of (height in cm x weight in kg / 3,600).
Question 3 · Hard
An obese man (48 years old, 130 kg, height 180 cm, ideal weight 75 kg) has serum creatinine 0.9 mg/dL. The pharmacist applies adjusted body weight, defined as ideal weight plus 0.4 times the excess, in the Cockcroft-Gault equation. Which clearance results?
1. A106 mL/min
2. B125 mL/min
3. C138 mL/min
4. D185 mL/min
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Answer: C · 138 mL/min
Adjusted weight = 75 + 0.4 x (130 - 75) = 97 kg. CrCl = (140 - 48) x 97 / (72 x 0.9) = 8,924 / 64.8 = 138 mL/min. Actual weight would give 185 mL/min and IBW 106 mL/min, so the choice of weight changes dosing decisions.
- A: 106 mL/min uses ideal weight and underestimates clearance.
- B: 125 mL/min does not follow from any standard weight.
- D: 185 mL/min uses actual body weight and overestimates clearance in obesity.
Remember this
In obesity use adjusted weight (IBW + 0.4 x excess) in Cockcroft-Gault, not actual weight.
Question 4 · Medium
A solution of 1:5,000 w/v expressed as a percentage is:
1. A0.02%
2. B0.002%
3. C0.2%
4. D0.5%
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Answer: A · 0.02%
1:5,000 means 1 g in 5,000 mL. In 100 mL that is 0.02 g, so the strength is 0.02% w/v.
- B: 0.002% would be 1:50,000.
- C: 0.2% would be 1:500.
- D: 0.5% would be 1:200.
Remember this
1:5,000 means 1 g in 5,000 mL, which is 0.02% w/v.
Question 5 · Medium
A pharmacist dilutes 10 mL of 50% w/v dextrose with water to a final volume of 500 mL. What is the final concentration?
1. A5% w/v
2. B0.1% w/v
3. C1% w/v
4. D10% w/v
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Answer: C · 1% w/v
The amount of dextrose is 10 mL x 50 g/100 mL = 5 g. The final strength is 5 g / 500 mL = 1 g/100 mL, or 1% w/v. The same result follows from C1V1 = C2V2.
- A: 5% would need a final volume of 100 mL.
- B: 0.1% would need a final volume of 5,000 mL.
- D: 10% would need a final volume of 50 mL.
Remember this
Use C1V1 = C2V2: here 10 mL of 50% in 500 mL gives 1%.
Question 6 · Medium
Pilocarpine nitrate 0.5% w/v eye drops are to be made isotonic in 100 mL with sodium chloride. The sodium chloride equivalent (E) of pilocarpine nitrate is 0.23. How much sodium chloride is needed?
1. A0.675 g
2. B0.785 g
3. C0.9 g
4. D0.115 g
Answer and explanation in LearnFree account
Question 7 · Medium
Ibuprofen 10 mg/kg per dose is ordered for a child weighing 12 kg. The suspension contains 100 mg/5 mL. How many millilitres are needed per dose?
1. A1.2 mL
2. B12 mL
3. C6 mL
4. D3 mL
Answer and explanation in LearnFree account
Question 8 · Medium
A patient is prescribed amoxicillin suspension 250 mg/5 mL, 500 mg three times daily for 7 days. How many 100 mL bottles must be dispensed at minimum?
1. A7 bottles
2. B3 bottles
3. C4 bottles
4. D2 bottles
Answer and explanation in LearnFree account
Question 9 · Easy
An antibiotic suspension contains 250 mg/5 mL. How many millilitres give a dose of 125 mg?
1. A10 mL
2. B5 mL
3. C2.5 mL
4. D1.25 mL
Answer and explanation in LearnFree account
Question 10 · Hard
A pharmacist prepares 60 mL of an isotonic eye drop containing ephedrine sulfate 1% w/v (sodium chloride equivalent 0.23). How much sodium chloride must be added?
1. A0.40 g
2. B0.68 g
3. C0.14 g
4. D0.54 g
Answer and explanation in LearnFree account
Question 11 · Medium
A pharmacist needs a 10% w/w ointment and has 20% and 5% ointments. In what ratio of parts (20% : 5%) should they be mixed?
1. A2 : 1
2. B1 : 2
3. C3 : 2
4. D1 : 3
Answer and explanation in LearnFree account
Question 12 · Easy
How many milligrams of adrenaline are in a 10 mL prefilled syringe labelled 1:10,000?
1. A100 mg
2. B0.1 mg
3. C1 mg
4. D10 mg
Answer and explanation in LearnFree account
Question 13 · Medium
An insulin infusion of 50 units in 50 mL is ordered at 0.05 units/kg/h for a patient weighing 90 kg. What pump rate is required?
1. A45 mL/h
2. B0.45 mL/h
3. C5 mL/h
4. D4.5 mL/h
Answer and explanation in LearnFree account
Question 14 · Easy
How many milliequivalents (mEq) of magnesium are in 1 mmol of magnesium sulphate?
1. A0.5 mEq
2. B1 mEq
3. C2 mEq
4. D4 mEq
Answer and explanation in LearnFree account
Question 15 · Easy
How many milligrams of lidocaine are in 1 mL of a 2% w/v injection?
1. A2 mg
2. B0.2 mg
3. C200 mg
4. D20 mg
Answer and explanation in LearnFree account
Question 16 · Hard
A stock solution is labelled 1:400 w/v. How many millilitres of it are needed to prepare 500 mL of a 1:2,000 w/v solution?
1. A100 mL
2. B125 mL
3. C400 mL
4. D80 mL
Answer and explanation in LearnFree account
Question 17 · Easy
A drug is prescribed at 10 mg/kg as a single dose. How much should a 20 kg child receive?
1. A200 mg
2. B2,000 mg
3. C20 mg
4. D100 mg
Answer and explanation in LearnFree account
Question 18 · Hard
A 1,000 mL infusion ordered over 8 hours started at 08:00. At 12:00 only 300 mL has infused. The prescriber still wants the bag finished by 16:00. What new rate is needed?
1. A175 mL/h
2. B125 mL/h
3. C150 mL/h
4. D233 mL/h
Answer and explanation in LearnFree account
Question 19 · Hard
A magnesium sulphate loading dose of 4 g (8 mL of 50% w/v solution) is added to saline to make 100 mL and is to be given over 20 minutes. What pump rate is needed?
1. A200 mL/h
2. B300 mL/h
3. C24 mL/h
4. D100 mL/h
Answer and explanation in LearnFree account
Question 20 · Medium
What is the approximate osmolarity of 1 litre of 3% w/v sodium chloride (MW 58.5)?
1. A513 mOsm/L
2. B770 mOsm/L
3. C855 mOsm/L
4. D1,026 mOsm/L
Answer and explanation in LearnFree account
Question 21 · Medium
A paediatric protocol scales an adult dose of 300 mg (for 1.73 m2) by body surface area. For a child of 0.55 m2 the dose is closest to:
1. A130 mg
2. B165 mg
3. C95 mg
4. D55 mg
Answer and explanation in LearnFree account
Question 22 · Medium
A man is 175 cm tall. Using the Devine formula for men (50 kg + 2.3 kg per inch over 5 feet), his ideal body weight is closest to (1 inch = 2.54 cm):
1. A70.5 kg
2. B75 kg
3. C64 kg
4. D80 kg
Answer and explanation in LearnFree account
Question 23 · Easy
Which value is the approximate osmolarity of 0.9% sodium chloride injection?
1. A308 mOsm/L
2. B154 mOsm/L
3. C616 mOsm/L
4. D280 mOsm/L
Answer and explanation in LearnFree account
Question 24 · Medium
A woman aged 58 years weighs 64 kg and has a serum creatinine of 0.9 mg/dL. Her creatinine clearance by Cockcroft-Gault is closest to:
1. A58 mL/min
2. B69 mL/min
3. C81 mL/min
4. D92 mL/min
Answer and explanation in LearnFree account
Question 25 · Easy
A 600 mL bag of fluid must run in over 8 hours. What pump rate should be set?
1. A48 mL/h
2. B7.5 mL/h
3. C75 mL/h
4. D150 mL/h
Answer and explanation in LearnFree account

25 more Pharmaceutical calculations questions

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Pharmaceutical calculations

Calcium gluconate (MW 430) 1 g is given for hypocalcaemia. Approximately how many mEq of calcium does it provide?

A patient is 170 cm tall and weighs 70 kg. What is the body surface area by the Mosteller formula, sqrt(height in cm x weight in kg / 3,600)?

An obese man (48 years old, 130 kg, height 180 cm, ideal weight 75 kg) has serum creatinine 0.9 mg/dL. The pharmacist applies adjusted body weight, defined as ideal weight plus 0.4 times the excess, in the Cockcroft-Gault equation. Which clearance results?

A solution of 1:5,000 w/v expressed as a percentage is:

A pharmacist dilutes 10 mL of 50% w/v dextrose with water to a final volume of 500 mL. What is the final concentration?

Pilocarpine nitrate 0.5% w/v eye drops are to be made isotonic in 100 mL with sodium chloride. The sodium chloride equivalent (E) of pilocarpine nitrate is 0.23. How much sodium chloride is needed?

Ibuprofen 10 mg/kg per dose is ordered for a child weighing 12 kg. The suspension contains 100 mg/5 mL. How many millilitres are needed per dose?

A patient is prescribed amoxicillin suspension 250 mg/5 mL, 500 mg three times daily for 7 days. How many 100 mL bottles must be dispensed at minimum?

An antibiotic suspension contains 250 mg/5 mL. How many millilitres give a dose of 125 mg?

A pharmacist prepares 60 mL of an isotonic eye drop containing ephedrine sulfate 1% w/v (sodium chloride equivalent 0.23). How much sodium chloride must be added?

A pharmacist needs a 10% w/w ointment and has 20% and 5% ointments. In what ratio of parts (20% : 5%) should they be mixed?

How many milligrams of adrenaline are in a 10 mL prefilled syringe labelled 1:10,000?

An insulin infusion of 50 units in 50 mL is ordered at 0.05 units/kg/h for a patient weighing 90 kg. What pump rate is required?

How many milliequivalents (mEq) of magnesium are in 1 mmol of magnesium sulphate?

How many milligrams of lidocaine are in 1 mL of a 2% w/v injection?

A stock solution is labelled 1:400 w/v. How many millilitres of it are needed to prepare 500 mL of a 1:2,000 w/v solution?

A drug is prescribed at 10 mg/kg as a single dose. How much should a 20 kg child receive?

A 1,000 mL infusion ordered over 8 hours started at 08:00. At 12:00 only 300 mL has infused. The prescriber still wants the bag finished by 16:00. What new rate is needed?

A magnesium sulphate loading dose of 4 g (8 mL of 50% w/v solution) is added to saline to make 100 mL and is to be given over 20 minutes. What pump rate is needed?

What is the approximate osmolarity of 1 litre of 3% w/v sodium chloride (MW 58.5)?

A paediatric protocol scales an adult dose of 300 mg (for 1.73 m2) by body surface area. For a child of 0.55 m2 the dose is closest to:

A man is 175 cm tall. Using the Devine formula for men (50 kg + 2.3 kg per inch over 5 feet), his ideal body weight is closest to (1 inch = 2.54 cm):

Which value is the approximate osmolarity of 0.9% sodium chloride injection?

A woman aged 58 years weighs 64 kg and has a serum creatinine of 0.9 mg/dL. Her creatinine clearance by Cockcroft-Gault is closest to:

A 600 mL bag of fluid must run in over 8 hours. What pump rate should be set?