Ptcb Quiz: Dosage Calculations
20 questions · exam conditions
0:00
Dosage CalculationsQuestion 1 of 20

A pediatric patient weighing 18 kg is prescribed a medication with a dosing schedule of 10 mg/kg/day, to be given in two divided doses. How many milligrams (mg) should be administered in a single dose?

180 mg
90 mg
360 mg
45 mg
← Back to quizzes

Ptcb Quiz

Ptcb Quiz: Dosage Calculations

Practice Dosage Calculations in Ptcb with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Dosage Calculations, giving you a quick way to practice the rules, question types, and explanations that matter most for Ptcb.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A pediatric patient weighing 18 kg is prescribed a medication with a dosing schedule of 10 mg/kg/day, to be given in two divided doses. How many milligrams (mg) should be administered in a single dose?

  1. 180 mg
  2. 90 mg (correct answer)
  3. 360 mg
  4. 45 mg
Explanation: The correct answer is 90 mg. First, calculate the total daily dose: 18 kg×10 mg/kg/day=180 mg/day18\ \text{kg} \times 10\ \text{mg/kg/day} = 180\ \text{mg/day}. Since the total daily dose is divided into two doses, divide by 2: 180 mg÷2=90 mg/dose180\ \text{mg} \div 2 = 90\ \text{mg/dose}.

Question 2

An IV order specifies that 1 liter of 0.9% sodium chloride should be infused over 10 hours. What is the correct flow rate in mL/hr?

  1. 10 mL/hr
  2. 50 mL/hr
  3. 100 mL/hr (correct answer)
  4. 1000 mL/hr
Explanation: The correct answer is 100 mL/hr. First, convert liters to milliliters: 1 L=1000 mL1\ \text{L} = 1000\ \text{mL}. Then, divide the total volume by the total time in hours: 1000 mL÷10 hours=100 mL/hr1000\ \text{mL} \div 10\ \text{hours} = 100\ \text{mL/hr}.

Question 3

A prescription for prednisone 5 mg tablets has the following directions: "Take 4 tabs daily for 2 days, then 3 tabs daily for 2 days, then 2 tabs daily for 2 days, then 1 tab daily for 2 days." What is the total number of tablets to dispense?

  1. 10 tablets
  2. 16 tablets
  3. 20 tablets (correct answer)
  4. 40 tablets
Explanation: The correct answer is 20 tablets. Calculate the number of tablets for each step of the taper and add them together: (4×2)+(3×2)+(2×2)+(1×2)=8+6+4+2=20 tablets(4 \times 2) + (3 \times 2) + (2 \times 2) + (1 \times 2) = 8 + 6 + 4 + 2 = 20\ \text{tablets}.

Question 4

A prescription for an oral liquid has the sig: "i tbsp po tid." What is the total volume in mL that the patient will take each day? (1 tbsp = 15 mL)

  1. 15 mL
  2. 30 mL
  3. 45 mL (correct answer)
  4. 60 mL
Explanation: The correct answer is 45 mL. The sig code "i tbsp" means one tablespoon, which is 15 mL. The sig code "tid" means three times a day. Therefore, the total daily volume is 15 mL/dose×3 doses/day=45 mL/day15\ \text{mL/dose} \times 3\ \text{doses/day} = 45\ \text{mL/day}.

Question 5

A patient is to take 7.5 mL of an oral solution twice a day for 14 days. What is the total volume in mL that should be dispensed?

  1. 105 mL
  2. 150 mL
  3. 210 mL (correct answer)
  4. 52.5 mL
Explanation: The correct answer is 210 mL. First, calculate the total daily volume: 7.5 mL/dose×2 doses/day=15 mL/day7.5\ \text{mL/dose} \times 2\ \text{doses/day} = 15\ \text{mL/day}. Then, multiply the daily volume by the duration of therapy: 15 mL/day×14 days=210 mL15\ \text{mL/day} \times 14\ \text{days} = 210\ \text{mL}.

Question 6

A pediatric patient weighing 18 kg is prescribed a medication with a dosing schedule of 10 mg/kg/day, to be given in two divided doses. How many milligrams (mg) should be administered in a single dose?

  1. 180 mg
  2. 90 mg (correct answer)
  3. 360 mg
  4. 45 mg
Explanation: The correct answer is 90 mg. First, calculate the total daily dose: 18 kg×10 mg/kg/day=180 mg/day18\ \text{kg} \times 10\ \text{mg/kg/day} = 180\ \text{mg/day}. Since the total daily dose is divided into two doses, divide by 2: 180 mg÷2=90 mg/dose180\ \text{mg} \div 2 = 90\ \text{mg/dose}.

Question 7

A prescription for prednisone 5 mg tablets has the following directions: "Take 4 tabs daily for 2 days, then 3 tabs daily for 2 days, then 2 tabs daily for 2 days, then 1 tab daily for 2 days." What is the total number of tablets to dispense?

  1. 10 tablets
  2. 16 tablets
  3. 20 tablets (correct answer)
  4. 40 tablets
Explanation: The correct answer is 20 tablets. Calculate the number of tablets for each step of the taper and add them together: (4×2)+(3×2)+(2×2)+(1×2)=8+6+4+2=20 tablets(4 \times 2) + (3 \times 2) + (2 \times 2) + (1 \times 2) = 8 + 6 + 4 + 2 = 20\ \text{tablets}.

Question 8

A patient receives a Z-Pak, which contains azithromycin 250 mg tablets. The instructions are to take 500 mg on Day 1, then 250 mg once daily on Days 2 through 5. What is the total amount of azithromycin in grams (g) taken during the entire course of therapy?

  1. 1.0 g
  2. 1.25 g
  3. 1.5 g (correct answer)
  4. 2.5 g
Explanation: The correct answer is 1.5 g. Calculate the total mg taken: Day 1 is 500 mg. Days 2-5 is 4 days, so 4×250 mg=1000 mg4 \times 250\ \text{mg} = 1000\ \text{mg}. The total course is 500 mg+1000 mg=1500 mg500\ \text{mg} + 1000\ \text{mg} = 1500\ \text{mg}. Convert mg to g: 1500 mg÷1000 mg/g=1.5 g1500\ \text{mg} \div 1000\ \text{mg/g} = 1.5\ \text{g}.

Question 9

A patient receives a Z-Pak, which contains azithromycin 250 mg tablets. The instructions are to take 500 mg on Day 1, then 250 mg once daily on Days 2 through 5. What is the total amount of azithromycin in grams (g) taken during the entire course of therapy?

  1. 1.0 g
  2. 1.25 g
  3. 1.5 g (correct answer)
  4. 2.5 g
Explanation: The correct answer is 1.5 g. Calculate the total mg taken: Day 1 is 500 mg. Days 2-5 is 4 days, so 4×250 mg=1000 mg4 \times 250\ \text{mg} = 1000\ \text{mg}. The total course is 500 mg+1000 mg=1500 mg500\ \text{mg} + 1000\ \text{mg} = 1500\ \text{mg}. Convert mg to g: 1500 mg÷1000 mg/g=1.5 g1500\ \text{mg} \div 1000\ \text{mg/g} = 1.5\ \text{g}.

Question 10

A prescription for an oral solution with a concentration of 50 mg/5 mL is written with the sig "Take 10 mL twice daily." How many milligrams (mg) of the drug will the patient take each day?

  1. 100 mg
  2. 200 mg (correct answer)
  3. 50 mg
  4. 250 mg
Explanation: The correct answer is 200 mg. First, determine the strength per mL: 50 mg÷5 mL=10 mg/mL50\ \text{mg} \div 5\ \text{mL} = 10\ \text{mg/mL}. Next, calculate the amount per dose: 10 mL/dose×10 mg/mL=100 mg/dose10\ \text{mL/dose} \times 10\ \text{mg/mL} = 100\ \text{mg/dose}. Finally, calculate the total daily dose: 100 mg/dose×2 doses/day=200 mg/day100\ \text{mg/dose} \times 2\ \text{doses/day} = 200\ \text{mg/day}.

Question 11

A physician prescribes amoxicillin 750 mg. The pharmacy has 250 mg tablets in stock. How many tablets should the patient take for one dose?

  1. 2 tablets
  2. 3 tablets (correct answer)
  3. 4 tablets
  4. 1.5 tablets
Explanation: The correct answer is 3 tablets. To find the number of tablets per dose, divide the prescribed dose by the strength of the available tablets. Calculation: 750 mg÷250 mg/tablet=3 tablets750\ \text{mg} \div 250\ \text{mg/tablet} = 3\ \text{tablets}.

Question 12

A patient is to take 7.5 mL of an oral solution twice a day for 14 days. What is the total volume in mL that should be dispensed?

  1. 105 mL
  2. 150 mL
  3. 210 mL (correct answer)
  4. 52.5 mL
Explanation: The correct answer is 210 mL. First, calculate the total daily volume: 7.5 mL/dose×2 doses/day=15 mL/day7.5\ \text{mL/dose} \times 2\ \text{doses/day} = 15\ \text{mL/day}. Then, multiply the daily volume by the duration of therapy: 15 mL/day×14 days=210 mL15\ \text{mL/day} \times 14\ \text{days} = 210\ \text{mL}.

Question 13

An IV order specifies that 1 liter of 0.9% sodium chloride should be infused over 10 hours. What is the correct flow rate in mL/hr?

  1. 10 mL/hr
  2. 50 mL/hr
  3. 100 mL/hr (correct answer)
  4. 1000 mL/hr
Explanation: The correct answer is 100 mL/hr. First, convert liters to milliliters: 1 L=1000 mL1\ \text{L} = 1000\ \text{mL}. Then, divide the total volume by the total time in hours: 1000 mL÷10 hours=100 mL/hr1000\ \text{mL} \div 10\ \text{hours} = 100\ \text{mL/hr}.

Question 14

A pharmacist prepares an IV admixture by adding 4 g of a medication to a 500 mL bag of D5W. What is the final concentration of the medication in mg/mL?

  1. 4 mg/mL
  2. 8 mg/mL (correct answer)
  3. 0.8 mg/mL
  4. 1.25 mg/mL
Explanation: The correct answer is 8 mg/mL. First, convert grams to milligrams: 4 g=4000 mg4\ \text{g} = 4000\ \text{mg}. Then, divide the total milligrams of the drug by the total volume in milliliters: 4000 mg÷500 mL=8 mg/mL4000\ \text{mg} \div 500\ \text{mL} = 8\ \text{mg/mL}.

Question 15

A vial of antibiotic powder must be reconstituted to a final concentration of 250 mg/mL. If a dose of 800 mg is required, how many milliliters (mL) should be drawn into the syringe?

  1. 3.2 mL (correct answer)
  2. 0.31 mL
  3. 2.5 mL
  4. 4.0 mL
Explanation: The correct answer is 3.2 mL. To find the volume needed, divide the desired dose by the concentration of the solution. Calculation: 800 mg÷250 mg/mL=3.2 mL800\ \text{mg} \div 250\ \text{mg/mL} = 3.2\ \text{mL}.

Question 16

A patient is prescribed an inhaler containing 120 metered doses. The instructions are to take 2 puffs in the morning and 2 puffs in the evening. How many days will this inhaler last?

  1. 15 days
  2. 30 days (correct answer)
  3. 45 days
  4. 60 days
Explanation: The correct answer is 30 days. First, calculate the total puffs per day: 2 puffs+2 puffs=4 puffs/day2\ \text{puffs} + 2\ \text{puffs} = 4\ \text{puffs/day}. Then, divide the total doses in the inhaler by the daily usage: 120 doses÷4 doses/day=30 days120\ \text{doses} \div 4\ \text{doses/day} = 30\ \text{days}.

Question 17

A patient uses 35 units of U-100 insulin daily. How many 10 mL vials are needed for a 90-day supply?

  1. 2 vials
  2. 3 vials
  3. 4 vials (correct answer)
  4. 5 vials
Explanation: The correct answer is 4 vials. First, calculate the total units needed: 35 units/day×90 days=3150 units35\ \text{units/day} \times 90\ \text{days} = 3150\ \text{units}. Next, find the number of units per vial (U-100 means 100 units/mL): 100 units/mL×10 mL/vial=1000 units/vial100\ \text{units/mL} \times 10\ \text{mL/vial} = 1000\ \text{units/vial}. Finally, divide the total units needed by the units per vial: 3150÷1000=3.153150 \div 1000 = 3.15. Since the patient cannot be dispensed a fraction of a vial, 4 vials must be dispensed.

Question 18

How many milligrams of active ingredient are in 250 mL of a 1:5000 solution?

  1. 5 mg
  2. 50 mg (correct answer)
  3. 500 mg
  4. 20 mg
Explanation: The correct answer is 50 mg. A 1:5000 solution contains 1 gram of solute in 5000 mL of solution. Set up a proportion: 1 g5000 mL=x g250 mL\frac{1\ \text{g}}{5000\ \text{mL}} = \frac{x\ \text{g}}{250\ \text{mL}}. Solving for x gives x=0.05 gx = 0.05\ \text{g}. Convert grams to milligrams: 0.05 g×1000 mg/g=50 mg0.05\ \text{g} \times 1000\ \text{mg/g} = 50\ \text{mg}.

Question 19

How many grams of sodium chloride are needed to prepare 1 liter of 0.9% normal saline solution?

  1. 0.9 g
  2. 9 g (correct answer)
  3. 90 g
  4. 900 g
Explanation: The correct answer is 9 g. A 0.9% solution means there are 0.9 grams of solute per 100 mL of solution. First, convert 1 liter to 1000 mL. Then, set up a proportion: 0.9 g100 mL=x g1000 mL\frac{0.9\ \text{g}}{100\ \text{mL}} = \frac{x\ \text{g}}{1000\ \text{mL}}. Cross-multiply: 100x=900100x = 900. Solve for x: x=9 gx = 9\ \text{g}.

Question 20

A pharmacy technician needs to prepare 240 g of a 2.5% ointment. The technician will use a 1% ointment and a 5% ointment. How many grams of the 5% ointment are needed?

  1. 60 g
  2. 90 g (correct answer)
  3. 150 g
  4. 180 g
Explanation: The correct answer is 90 g. This problem can be solved using alligation. The difference between the desired strength (2.5%) and the lower strength (1%) is 1.5. This means 1.5 parts of the higher strength are needed. The difference between the higher strength (5%) and the desired strength (2.5%) is 2.5. This means 2.5 parts of the lower strength are needed. The total number of parts is 1.5+2.5=41.5 + 2.5 = 4. The proportion of the 5% ointment needed is 1.54\frac{1.5}{4}. Calculate the amount: 1.54×240 g=90 g\frac{1.5}{4} \times 240\ \text{g} = 90\ \text{g}.