Pharmacology Quiz: Weight Based Dosing

20 questions · exam conditions

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Weight Based DosingQuestion 1 of 20

An 80-kg patient receives an initial IV push dose of an antiarrhythmic drug at 0.5 mg/kg. The order states, "If arrhythmia persists, increase dose by 20% for the next administration." If the patient's arrhythmia persists, what will be the new dose in mg?

8 mg

40 mg

48 mg

56 mg

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Pharmacology Quiz

Pharmacology Quiz: Weight Based Dosing

Practice Weight Based Dosing in Pharmacology 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 Weight Based Dosing, giving you a quick way to practice the rules, question types, and explanations that matter most for Pharmacology.

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

8 mg
40 mg
48 mg (correct answer)
56 mg

Explanation: First, calculate the initial dose administered:

80 \text{ kg} \times 0.5 \text{ mg/kg} = 40 \text{ mg}

. Next, calculate the 20% increase:

40 \text{ mg} \times 0.20 = 8 \text{ mg}

. The new dose is the initial dose plus the increase:

40 \text{ mg} + 8 \text{ mg} = 48 \text{ mg}

. Alternatively, one can calculate the new dose directly:

40 \text{ mg} \times 1.20 = 48 \text{ mg}

Question 2

A 198-lb patient requires a heparin bolus of 80 units/kg followed by a continuous infusion. The pharmacy stocks heparin vials containing 5,000 units/mL. What volume of heparin should be administered for the bolus dose?

1.44 mL (correct answer)
1.58 mL
3.17 mL
3.96 mL

Explanation: First, convert the patient's weight to kg:

198 \text{ lbs} \div 2.2 \text{ lbs/kg} = 90 \text{ kg}

. Second, calculate the total number of units for the bolus dose:

90 \text{ kg} \times 80 \text{ units/kg} = 7200 \text{ units}

. Finally, calculate the volume to be administered using the available concentration:

7200 \text{ units} \div 5000 \text{ units/mL} = 1.44 \text{ mL}

Question 3

An infant weighs 8.8 lbs and requires an antibiotic at a dose of 25 mg/kg/day, divided into two doses. The oral suspension is available at a concentration of 125 mg/5 mL. What volume in mL is needed for a single morning dose?

1.0 mL
2.0 mL (correct answer)
4.0 mL
8.8 mL

Explanation: First, convert the infant's weight to kg:

8.8 \text{ lbs} \div 2.2 \text{ lbs/kg} = 4 \text{ kg}

. Second, calculate the total daily dose:

4 \text{ kg} \times 25 \text{ mg/kg/day} = 100 \text{ mg/day}

. Third, determine the amount for a single dose:

100 \text{ mg/day} \div 2 \text{ doses} = 50 \text{ mg/dose}

. Finally, calculate the volume of the suspension. The concentration is

125 \text{ mg}/5 \text{ mL}

, which simplifies to

25 \text{ mg/mL}

. The volume is

50 \text{ mg} \div 25 \text{ mg/mL} = 2.0 \text{ mL}

Question 4

A 10-year-old male weighing 121 lbs is prescribed intravenous vancomycin. The standard pediatric dose is 60 mg/kg/day, divided every 6 hours. However, the absolute maximum daily dose for this medication is 3 g/day. What is the appropriate single dose in mg to administer?

750 mg (correct answer)
825 mg
1815 mg
3000 mg

Explanation: First, convert the patient's weight to kg:

121 \text{ lbs} \div 2.2 \text{ lbs/kg} = 55 \text{ kg}

. Next, calculate the theoretical total daily dose based on weight:

55 \text{ kg} \times 60 \text{ mg/kg/day} = 3300 \text{ mg/day}

. This dose (3.3 g/day) exceeds the specified absolute maximum daily dose of 3 g/day (3000 mg/day). Therefore, the dose must be capped at 3000 mg/day. Since the medication is administered every 6 hours (4 times a day), the single dose is:

3000 \text{ mg/day} \div 4 \text{ doses} = 750 \text{ mg/dose}

Question 5

A 165-lb patient in the ICU is receiving a norepinephrine infusion prepared as 4 mg in 250 mL of D5W. The current infusion rate is 21 mL/hr. What is the current dose the patient is receiving in mcg/kg/min?

0.07 mcg/kg/min (correct answer)
0.12 mcg/kg/min
0.45 mcg/kg/min
7.0 mcg/kg/min

Explanation: This multi-step problem requires working backward. First, convert weight:

165 \text{ lbs} \div 2.2 = 75 \text{ kg}

. Second, find the drug concentration:

4 \text{ mg} \div 250 \text{ mL} = 0.016 \text{ mg/mL}

. Convert concentration to mcg/mL:

0.016 \text{ mg/mL} \times 1000 = 16 \text{ mcg/mL}

. Third, calculate the dose rate in mcg/hr:

21 \text{ mL/hr} \times 16 \text{ mcg/mL} = 336 \text{ mcg/hr}

. Fourth, convert the rate to mcg/min:

336 \text{ mcg/hr} \div 60 \text{ min/hr} = 5.6 \text{ mcg/min}

. Finally, normalize to patient weight:

5.6 \text{ mcg/min} \div 75 \text{ kg} \approx 0.075 \text{ mcg/kg/min}

, which rounds to 0.07 mcg/kg/min.

Question 6

A patient weighing 80 kg is to receive a loading dose of phenytoin at 15 mg/kg. The medication is to be infused at a rate not exceeding 50 mg/min. What is the minimum duration, in minutes, for this infusion?

16 minutes
48 minutes
30 minutes
24 minutes (correct answer)

Explanation: When you encounter dosing calculations involving infusion rates, you need to determine the total dose required and then apply the maximum safe infusion rate to find the minimum time needed. First, calculate the total loading dose:

80 \text{ kg} \times 15 \text{ mg/kg} = 1200 \text{ mg}

Next, apply the maximum infusion rate constraint. Since phenytoin cannot be infused faster than 50 mg/min, divide the total dose by this rate:

\frac{1200 \text{ mg}}{50 \text{ mg/min}} = 24 \text{ minutes}

This gives you the minimum safe duration for the infusion. Looking at the wrong answers: A) 16 minutes would require an infusion rate of 75 mg/min (1200 ÷ 16), which exceeds the 50 mg/min safety limit and could cause cardiovascular toxicity. B) 48 minutes represents a calculation error where someone might have doubled the correct answer or miscalculated the dose as 2400 mg. C) 30 minutes would only deliver 1500 mg total if infusing at maximum rate, suggesting confusion about the dose calculation. Answer D) 24 minutes correctly respects both the prescribed dose (1200 mg) and the safety constraint (≤50 mg/min). Study tip: For IV medication calculations, always work through three steps: calculate total dose needed, identify the rate limitation, then solve for time using the formula Time = Total Dose ÷ Maximum Rate. This systematic approach prevents errors and ensures patient safety parameters are respected.

Question 7

A 25-kg child is prescribed an antibiotic with a recommended dose of 20-40 mg/kg/day, given in divided doses every 8 hours. The physician orders 150 mg every 8 hours. Which statement accurately assesses the appropriateness of this ordered dose?

The dose is appropriate, as the calculated dose per administration (6 mg/kg) is a common therapeutic dose.
The dose is too high, as the total daily dose exceeds the maximum recommended daily dose.
The dose is too low, as the total daily dose is below the minimum recommended daily dose. (correct answer)
The dose is appropriate, as the total daily dose of 450 mg is sufficient for a 25-kg child.

Explanation: First, calculate the safe therapeutic range for the total daily dose. Minimum daily dose:

25 \text{ kg} \times 20 \text{ mg/kg/day} = 500 \text{ mg/day}

. Maximum daily dose:

25 \text{ kg} \times 40 \text{ mg/kg/day} = 1000 \text{ mg/day}

. Next, calculate the total daily dose the patient is actually receiving:

150 \text{ mg/dose} \times 3 \text{ doses/day} = 450 \text{ mg/day}

. Comparing the ordered daily dose (450 mg) to the recommended range (500-1000 mg), the ordered dose is below the minimum therapeutic threshold.

Question 8

A 154-lb patient requires amikacin at a dose of 15 mg/kg/day, administered in two equally divided doses. The pharmacy supplies amikacin in vials with a concentration of 500 mg/2 mL. How many milliliters should be administered for a single dose?

1.1 mL
2.1 mL (correct answer)
4.2 mL
4.6 mL

Explanation: This is a multi-step calculation. First, convert the patient's weight from pounds (lbs) to kilograms (kg):

154 \text{ lbs} \div 2.2 \text{ lbs/kg} = 70 \text{ kg}

. Second, calculate the total daily dose in mg:

70 \text{ kg} \times 15 \text{ mg/kg/day} = 1050 \text{ mg/day}

. Third, determine the single dose amount, as the total daily dose is divided into two doses:

1050 \text{ mg} \div 2 = 525 \text{ mg}

. Finally, calculate the volume to administer based on the available concentration (500 mg/2 mL, which is 250 mg/mL):

525 \text{ mg} \div 250 \text{ mg/mL} = 2.1 \text{ mL}

Question 9

A 70-kg patient with normal renal function is ordered enoxaparin for DVT prophylaxis at a dose of 1 mg/kg subcutaneously every 12 hours. The pharmacy dispenses pre-filled syringes of 80 mg/0.8 mL. How should the dose be administered?

Administer the full 0.8 mL syringe.
Administer 0.7 mL from the syringe. (correct answer)
Administer 0.6 mL from the syringe.
Request a 70 mg pre-filled syringe from pharmacy.

Explanation: First, calculate the required dose for the patient:

70 \text{ kg} \times 1 \text{ mg/kg} = 70 \text{ mg}

. Next, determine the concentration of the provided syringe:

80 \text{ mg} \div 0.8 \text{ mL} = 100 \text{ mg/mL}

. Now, calculate the volume needed to deliver the 70 mg dose:

70 \text{ mg} \div 100 \text{ mg/mL} = 0.7 \text{ mL}

. Therefore, 0.7 mL should be administered from the 80 mg/0.8 mL syringe. While requesting an exact dose syringe might be an option in some institutions, the question asks how the dose should be administered from the supplied syringe.

Question 10

1.44 mL (correct answer)
1.58 mL
3.17 mL
3.96 mL

Explanation: First, convert the patient's weight to kg:

198 \text{ lbs} \div 2.2 \text{ lbs/kg} = 90 \text{ kg}

. Second, calculate the total number of units for the bolus dose:

90 \text{ kg} \times 80 \text{ units/kg} = 7200 \text{ units}

. Finally, calculate the volume to be administered using the available concentration:

7200 \text{ units} \div 5000 \text{ units/mL} = 1.44 \text{ mL}

Question 11

1.1 mL
2.1 mL (correct answer)
4.2 mL
4.6 mL

Explanation: This is a multi-step calculation. First, convert the patient's weight from pounds (lbs) to kilograms (kg):

154 \text{ lbs} \div 2.2 \text{ lbs/kg} = 70 \text{ kg}

. Second, calculate the total daily dose in mg:

70 \text{ kg} \times 15 \text{ mg/kg/day} = 1050 \text{ mg/day}

. Third, determine the single dose amount, as the total daily dose is divided into two doses:

1050 \text{ mg} \div 2 = 525 \text{ mg}

. Finally, calculate the volume to administer based on the available concentration (500 mg/2 mL, which is 250 mg/mL):

525 \text{ mg} \div 250 \text{ mg/mL} = 2.1 \text{ mL}

Question 12

750 mg (correct answer)
825 mg
1815 mg
3000 mg

Explanation: First, convert the patient's weight to kg:

121 \text{ lbs} \div 2.2 \text{ lbs/kg} = 55 \text{ kg}

. Next, calculate the theoretical total daily dose based on weight:

55 \text{ kg} \times 60 \text{ mg/kg/day} = 3300 \text{ mg/day}

3000 \text{ mg/day} \div 4 \text{ doses} = 750 \text{ mg/dose}

Question 13

A 68-kg patient requires a dobutamine infusion at a rate of 5 mcg/kg/min. The pharmacy prepares an infusion bag containing 250 mg of dobutamine in 250 mL of D5W. At what rate, in mL/hr, should the infusion pump be set?

10.2 mL/hr
20.4 mL/hr (correct answer)
81.6 mL/hr
204 mL/hr

Explanation: First, calculate the patient's dose in mcg/min:

5 \text{ mcg/kg/min} \times 68 \text{ kg} = 340 \text{ mcg/min}

. Next, convert this rate to mg/hr:

340 \frac{\text{mcg}}{\text{min}} \times \frac{1 \text{ mg}}{1000 \text{ mcg}} \times \frac{60 \text{ min}}{1 \text{ hr}} = 20.4 \text{ mg/hr}

. Then, determine the concentration of the solution:

250 \text{ mg} \div 250 \text{ mL} = 1 \text{ mg/mL}

. Finally, calculate the infusion rate in mL/hr:

\frac{20.4 \text{ mg/hr}}{1 \text{ mg/mL}} = 20.4 \text{ mL/hr}

Question 14

A 3-year-old child weighing 15 kg is prescribed ceftriaxone 50 mg/kg IM as a single dose. The medication is available as a 1 g vial of powder. The reconstitution instructions state: "Add 3.6 mL of sterile water to yield a final concentration of 250 mg/mL." What volume of the reconstituted solution should be drawn up for administration?

0.75 mL
2.7 mL
3.0 mL (correct answer)
3.6 mL

Explanation: First, calculate the required dose in mg:

15 \text{ kg} \times 50 \text{ mg/kg} = 750 \text{ mg}

. The problem provides the final concentration of the reconstituted solution, which is 250 mg/mL. The volume of diluent added (3.6 mL) and the total vial size (1 g) are relevant for preparation but not for the final volume calculation once concentration is known. Calculate the volume to administer using the final concentration:

750 \text{ mg} \div 250 \text{ mg/mL} = 3.0 \text{ mL}

Question 15

8 mg
40 mg
48 mg (correct answer)
56 mg

Explanation: First, calculate the initial dose administered:

80 \text{ kg} \times 0.5 \text{ mg/kg} = 40 \text{ mg}

. Next, calculate the 20% increase:

40 \text{ mg} \times 0.20 = 8 \text{ mg}

. The new dose is the initial dose plus the increase:

40 \text{ mg} + 8 \text{ mg} = 48 \text{ mg}

. Alternatively, one can calculate the new dose directly:

40 \text{ mg} \times 1.20 = 48 \text{ mg}

Question 16

0.07 mcg/kg/min (correct answer)
0.12 mcg/kg/min
0.45 mcg/kg/min
7.0 mcg/kg/min

Explanation: This multi-step problem requires working backward. First, convert weight:

165 \text{ lbs} \div 2.2 = 75 \text{ kg}

. Second, find the drug concentration:

4 \text{ mg} \div 250 \text{ mL} = 0.016 \text{ mg/mL}

. Convert concentration to mcg/mL:

0.016 \text{ mg/mL} \times 1000 = 16 \text{ mcg/mL}

. Third, calculate the dose rate in mcg/hr:

21 \text{ mL/hr} \times 16 \text{ mcg/mL} = 336 \text{ mcg/hr}

. Fourth, convert the rate to mcg/min:

336 \text{ mcg/hr} \div 60 \text{ min/hr} = 5.6 \text{ mcg/min}

. Finally, normalize to patient weight:

5.6 \text{ mcg/min} \div 75 \text{ kg} \approx 0.075 \text{ mcg/kg/min}

, which rounds to 0.07 mcg/kg/min.

Question 17

A patient weighing 60 kg is prescribed a chemotherapy agent at a dose of 30 mg/m². The patient's Body Surface Area (BSA) is calculated to be 1.7 m². The order specifies that if the weight-based dose of 50 mg/kg exceeds the BSA-based dose, the lower of the two should be administered. Which dose should the patient receive?

51 mg (correct answer)
1800 mg
3000 mg
The doses cannot be compared without the patient's height.

Explanation: This question requires calculating two different potential doses and then comparing them based on the provided rule. First, calculate the BSA-based dose:

1.7 \text{ m}^2 \times 30 \text{ mg/m}^2 = 51 \text{ mg}

. Second, calculate the weight-based dose:

60 \text{ kg} \times 50 \text{ mg/kg} = 3000 \text{ mg}

. The order specifies administering the lower of the two doses. Comparing the two calculated doses, 51 mg is lower than 3000 mg. Therefore, the patient should receive 51 mg. The BSA is already provided, so height is not needed.

Question 18

1.0 mL
2.0 mL (correct answer)
4.0 mL
8.8 mL

Explanation: First, convert the infant's weight to kg:

8.8 \text{ lbs} \div 2.2 \text{ lbs/kg} = 4 \text{ kg}

. Second, calculate the total daily dose:

4 \text{ kg} \times 25 \text{ mg/kg/day} = 100 \text{ mg/day}

. Third, determine the amount for a single dose:

100 \text{ mg/day} \div 2 \text{ doses} = 50 \text{ mg/dose}

. Finally, calculate the volume of the suspension. The concentration is

125 \text{ mg}/5 \text{ mL}

, which simplifies to

25 \text{ mg/mL}

. The volume is

50 \text{ mg} \div 25 \text{ mg/mL} = 2.0 \text{ mL}

Question 19

A 50-kg patient is prescribed Drug Z at 4 mg/kg/day. The drug's half-life requires it to be given in 4 divided doses. The drug is supplied as 50 mg tablets that can be split in half. How many tablets should be administered per dose?

One-half tablet
Two tablets
One and one-half tablets
One tablet (correct answer)

Explanation: Dosage calculations in pharmacology require you to work systematically through total daily dose, individual dose amounts, and finally tablet quantities. This type of problem tests your ability to convert between different units while accounting for drug formulation. Let's calculate step by step. First, determine the total daily dose: 50 kg × 4 mg/kg/day = 200 mg/day. Since the drug is given in 4 divided doses throughout the day, each individual dose is 200 mg ÷ 4 = 50 mg per dose. Finally, convert to tablets: with 50 mg tablets available, you need 50 mg ÷ 50 mg/tablet = 1 tablet per dose. Now let's examine why the other options are incorrect. Choice A (one-half tablet) would only provide 25 mg per dose, giving a total daily dose of 100 mg—half of what's prescribed. Choice B (two tablets) would deliver 100 mg per dose, resulting in 400 mg daily, which is double the intended dose and potentially toxic. Choice C (one and one-half tablets) would provide 75 mg per dose for a total of 300 mg daily, which is 50% higher than prescribed. Choice D (one tablet) correctly provides exactly 50 mg per dose and 200 mg daily as prescribed. Study tip: Always work through dosage calculations in order: patient weight × dose per kg = total daily dose, then divide by frequency for individual dose, then convert to available tablet strength. Double-check your math by working backward—does your final answer multiplied by frequency equal the intended daily dose?

Question 20

Administer the full 0.8 mL syringe.
Administer 0.7 mL from the syringe. (correct answer)
Administer 0.6 mL from the syringe.
Request a 70 mg pre-filled syringe from pharmacy.

Explanation: First, calculate the required dose for the patient:

70 \text{ kg} \times 1 \text{ mg/kg} = 70 \text{ mg}

. Next, determine the concentration of the provided syringe:

80 \text{ mg} \div 0.8 \text{ mL} = 100 \text{ mg/mL}

. Now, calculate the volume needed to deliver the 70 mg dose:

70 \text{ mg} \div 100 \text{ mg/mL} = 0.7 \text{ mL}