CH 5 DOSAGE CALCULATIONS

Question 1

1. The nurse is calculating a drug dosage and converting from milligrams to grams. What measurement system is the nurse using?

A) Metric system
B) Apothecary system
C) Household system
D) Avoirdupois system

Answer 1

Ans: A
Feedback:
The metric system is the most widely used system of measurement in the world; it is based on the decimal system. The gram is the basic unit of solid measure, and the liter unit of liquid measure. The apothecary system uses the grain as the basic unit of solid measure. The household system uses the pound as the basic unit of measure. The avoirdupois system uses ounces and grains, but it is mostly used by drug manufacturers for bulk medications.

Question 2

2. The nurse teaches a young mother the importance of administering appropriate dosages of acetaminophen (Tylenol) and determines further teaching is needed when the mother makes what statement?

A) “The children’s dosage will change with time as they grow.”
B) “My baby’s dose of Tylenol is about 1 half an adult dose.”
C) “It is important to give the right dose to prevent toxic effects of the medication.”
D) “My children’s dose of Tylenol should be based on their weight or age.”

Answer 2

Ans: B
Feedback:
A child’s dose is never based on an adult’s dose. A child’s dosage is based on weight and age and will change with age as they grow. Larger than directed dosages can result in toxic effects of this medication.

Question 3

3. A nurse calculates the pediatric patient’s medication dosage using Clark’s rule and uses what formula?

A) Infant’s age in months/150 months times the average adult dose
B) Child’s age in years/child’s age in years plus 12 times the average adult dose
C) Weight of child in pounds/150 pounds times the average adult dose
D) Surface area in square meters/1.73 times the average adult dose

Answer 3

Ans: C
Feedback:
Clark’s rule uses the child’s weight to calculate the dose and assumes the adult dose is based on a 150-pound person. Fried’s rule applies to a child younger than 1 year of age and assumes that an adult dose would be appropriate for a child who is 12.5 years (150 months) old. Young’s rule applies to children 1 to 12 years of age. Surface area calculation of a child’s dose is determined with the use of a nomogram including the child’s height and weight.

Question 4

4. The nurse receives a new medication order for a patient to administer 240 mg of medication per day in equally divided doses every 6 hours. How many mg of the drug should the nurse administer for each dose?

Answer 4

Ans: 60 mg
Feedback:
Because there are 24 hours in a day, giving a drug every 6 hours would mean giving the drug 4 times a day. Because the total daily dose is 240 mg, dividing that dose by 4 would mean each dose should be 60 mg.

Question 5

5. A physician orders 500 mL of IV solution be administered over 8 hours. If the IV infusion set delivers 15 drops per mL, how many drops per minute should the nurse administer to the patient?

A) 15 drops/min
B) 20 drops/min
C) 32 drops/min
D) 64 drops/min

Answer 5

Ans: A

Feedback:
If a patient was to receive 500 mL in 8 hours, dividing 500 by 8 would mean that the patient would receive 62.5 mL in 1 hour, or 60 min. Setting up the equation, 15 drops/mL/X equals 62.5 mL/60 min; cross-multiplying, the answer will be 15 drops/min.

Question 6

6. The nurse is teaching a diabetic patient to self-administer Humulin insulin, supplied in a vial labeled 100 units/mL. The provider has ordered 32 units of Humulin insulin to be taken each morning. How many mL of insulin would the patient prepare for one dose?

A) 0.032 mL
B) 0.32 mL
C) 3.2 mL
D) 0.64 mL

Answer 6

Ans: B
Feedback:
There are 100 units in each mL. Divide that amount by 32 units for the answer (0.32 mL).

Question 7

7. The provider orders a maintenance dose of oral aminophylline, 3 mg/kg every 6 hour. The patient weighs 50 kg. How many mg should the nurse administer to the patient in a 24-hour period?

Answer 7

Ans: 600milligram
Feedback:
The patient’s weight times the number of milligram/kilogram will provide daily dosage of medication: 50 kg × 3 mg/kg = 150 mg per dose. The patient is to receive a dose every 6 hours. The number of hours in a day divided by the number of hours separating each dose supplies the number of dosages the patient receives per day: 24 hours ÷ 6 hours between doses = 4 doses per day. If each dose is 150 mg and the patient receives 4 of these doses a day, the total amount of medication received is 150 mg × 4 daily doses = 600 mg.

Question 8

8. The physician writes an order for oxazepam for a 6-year-old child. The nurse verifies that there is no established dosage for children 6 to 12 years of age for oxazepam. The nurse knows that the usual adult dose is 10 mg tid. What would the nurse calculate the appropriate dose to be?

A) 0.03 mg tid
B) 0.3 mg tid
C) 1.8 mg tid
D) 3.3 mg tid

Answer 8

Ans: D
Feedback:
Because the nurse knows only the child’s age, the nurse would need to use Young’s rule to determine the appropriate dosage. The formula for Young’s rule is: Child’s dose = child’s age in years ÷ (child’s age + 12) × average adult dose. Using the information provided in the question: Dose = 6 ÷ (6 + 12) × 10 mg = 6 ÷ 18 × 10 = 0.33 × 10 = 3.3.

Question 9

9. A newly admitted patient has orders to receive 1,000 mL of normal saline IV over 8 hours. If the IV infusion set is a microdrip set that delivers 60 drops per mL, how many drops per minute should the nurse administer to the patient?

A) 60 drops/min
B) 125 drops/min
C) 240 drops/min
D) 480 drops/min

Answer 9

Ans: B
Feedback:
If a patient was to receive 1,000 mL in 8 hours, dividing 1000 by 8 would mean that the patient would receive 125 mL in 1 hour, or 60 minutes. Setting up the equation, 60 drops/mL ÷ X = 125 mL/60 minutes; cross-multiplying, the answer is 125 drops/min.

Question 10

10. The nurse is preparing to administer cefadroxil 1 g PO. The medication is supplied in 500-mg tablets. How many tablets will the nurse administer?

A) 0.5 tablet
B) 1 tablet
C) 2 tablets
D) 3 tablets

Answer 10

Ans: C
Feedback:
Convert 1 g to mg by multiplying 1 g times 1,000 mg. There are 500-mg in each tablet. Dividing the 1000 mg prescribed dosage by 500-mg available dosage, the answer is two tablets.

Question 11

11. The nurse begins administering 500 mL of 5% dextrose and water solution at 01:00 to run over 4 hours. At 02:00, the nurse administers 80 mg gentamicin in 50 cc normal saline to infuse over 30 minutes. How many mL of fluid will the nurse administer to the patient between 02:00 and 03:00?

A) 175 mL
B) 150 mL
C) 125 mL
D) 100 mL

Answer 11

Ans: A
Feedback:
The patient is receiving 500 mL over 4 hours. To determine how much fluid is infusing per hour = 500 mL ÷ 4 = 125. In addition to the 125 mL of IV solution, the patient also receives 50 mL of gentamicin during the 02:00 to 03:00 hour. 125 mL + 50 mL = 175 total mL of fluid received during this hour.

Question 12

12. An adult patient with renal cancer, weighing 95 kg, is to receive vincristine 25 mcg/kg/day IV. What is the dosage of vincristine that the nurse should administer to the patient daily in mg? __________

Answer 12

Ans: 2.375 mg
Feedback:
This order requires 25 mcg of medication for every 1 kg of body weight. The patient weighs 95 kg. To determine total dosage multiply weight times mcg of medication: 25 × 95 = 2,375 mcg. Convert mcg to mg by moving the decimal three places to the left, or you can divide 2,375 by 1,000 because there are 1,000 mcg per mg.

Question 13

13. The nurse is preparing medication for a 30-month-old child with otitis media in the right ear. The child weighs 33 pounds. The physician has ordered Keflex, 50 mg/kg/d in equally divided doses every 8 hours. The medication concentration is 250 mg/5 mL. How many milliliters should the nurse give the toddler for each dose?

Answer 13

Ans: 5 mL
Feedback:
To calculate the correct dosage, the nurse first converts the child’s weight from pounds to kilograms by dividing weight in pounds by 2.2 (2.2 lb = 1 kg). 33 pounds ÷ 2.2 pounds/kg = 15 kg. The child is to receive 50 mg for every kilogram. To determine this child’s dosage multiply weight times daily dose (15 kg × 50 mg/kg = 750 mg). Thus, 750 mg is to be administered in equally divided dosages every 8 hours, or 3 times a day. 750 mg ÷ 3 = 250 mg/dose. There is 250 mg in 5 mL of medication so the patient would be given 5 mL.

Question 14

14. An adolescent is admitted to the intensive care unit with diabetic ketoacidosis. The nurse prepares a continuous insulin infusion of 100 units (U) regular insulin in 500 milligram normal saline. When documenting this medication, how many units of regular insulin will this patient receive per milligram of IV solution?

A) 0.175 U/milligram
B) 0.2 U/milligram
C) 0.25 U/milligram
D) 0.5 U/milligram

Answer 14

Ans: B
Feedback:
The problem tells us there is 100 U/500 milligram. To determine how many units are in each milligram, divide both numbers by 500: 100 U ÷ 500/500 milligram÷ 500 = 0.2 U/1 milligram.

Question 15

15. The patient drinks 18 ounces of fluid at lunchtime. How many milliliters of intake will the nurse document?

A) 1.7 mL
B) 0.6 mL
C) 540 mL
D) 54 mL

Answer 15

Ans: C Feedback:
1 ounce = 30 mL. Using the ratio-and-proportion method: 1 oz/30 mL = 18 oz/X. Cross-multiply to determine the patient drank 540 mL of fluid.

Question 16

16. The pediatric nurse is caring for a child who weighs 44 pounds. The physician has ordered methylprednisolone sodium succinate (Solu-Medrol), 0.03 mg/kg/d IV in normal saline. How many milligrams of medication will the nurse prepare?

A) 6.5
B) 6
C) 0.65
D) 0.6

Answer 16

Ans: D
Feedback:
First convert the child’s weight to kilograms by dividing 44 pounds by 2.2 kg/1 pound = 20 kg. Multiply the dosage times the child’s weight: 20 kg × 0.03 mg/kg/d = 0.6 mg/d

Question 17

17. The nurse is to infuse 100 mL of 5% dextrose and water solution containing an IV antibiotic over 30 minutes. The infusion set delivers 10 gtt/mL. How many drops per minute will the nurse administer?

A) 33 gtt/min
B) 30.3 gtt/min
C) 30 gtt/min
D) 3 gtt/min

Answer 17

Ans: A Feedback:
Use the following ratio to determine how many drops of fluid to administer per minute: Using the information from this problem:
drops/minutes = (100 ×10)/30 = 1,000/30 = 33.3
Because it is not possible to deliver 0.3 drops, round 33.3 to 33 gtt/min.

Question 18

18. An 80-year-old patient with internal bleeding is admitted through the emergency room after a motor vehicle accident. The physician has ordered 2 units of packed red blood cells (1 unit is 250 mL) to infuse over 1 hour each. The drip rate on the blood administration set is10 gtt/mL. The nurse administers how many drops per minute to infuse the blood as ordered?

A) 47
B) 42
C) 37
D) 32

Answer 18

Ans: B
Feedback:
Use the following ratio to determine how many drops of fluid to administer per minute:
Using the information from this problem:
drops/minute = 250 × 10/60 = 2,500/60 = 41.7
Because it is not possible to deliver 0.7 of a drop, round 41.7 to 42 minutes

Question 19

19. The physician prescribes 250 mg of a drug. The information on the drug vial says the concentration is 500 mg/mL. How much of the drug will the nurse prepare?

A) 0.25 mL
B) 0.33 mL
C) 0.5 mL
D) 0.75 mL

Answer 19

Ans: C Feedback:

To determine amount to prepare: 500 mg/1 mL = 250 mg/X. Cross-multiply to determine the nurse will prepare 0.5 mL.

Question 20

20. An 81-year-old patient with congestive heart failure has been sent to a cardiologist who prescribes digoxin (Lanoxin) 0.125 mg PO every morning. The pharmacy dispenses pills that contain 0.25 mg of Lanoxin. How many pills should the nurse teach the patient to take every morning?

A) 2
B) 1.5
C) 1
D) 0.5

Answer 20

Ans: D Feedback:
(amount of drug available)/(1 tablet) =
(amount of drug prescribed)/(# tablets to give)

0.25 mg/1 tablet = 0.125 mg dose/X. Cross-multiply to determine 0.5 or 1/2 of a tablet is to be taken daily. The nurse may request the pharmacy dispense a different concentration to prevent the patient from having to cut the tablet in half.

Question 21

21. A patient with diabetic ketoacidosis is to receive a continuous infusion of regular insulin. The physician orders 1 L of 5% dextrose and water solution to run at 150 mL/h once the patient’s blood glucose has reached 250 mg/dL. The drip factor of the tubing is 15 gtt/mL. How many drops per minute will the nurse deliver?

A) 0.25 gtt/min
B) 62 gtt/min
C) 37 gtt/min
D) 250 gtt/min

Answer 21

Ans: C
Feedback:
Use the following ratio to determine how many drops of fluid to administer per minute:
Using the information from this problem:
150 mL × 150 gtts 2,250
drops/minutes = hour 60 mL = 60 = 37.5 gtts/min.
37.5 can be rounded to 37 or 38 gtt/min.

Question 22

22. A patient has orders to receive 2 L of IV fluid over a 24-hour period with 1⁄2 this amount to be infused in the first 10 hours of treatment. How many milliliters per hour will the nurse administer during the first 10 hours of the infusion?

A) 50 mL/h
B) 100 mL/h
C) 83 mL/h
D) 200 mL/h

Answer 22

Ans: B Feedback:
1⁄2 of the 2 liters is to infuse in the first 10 hours. 1⁄2 of 2 = 1 L; 1 L = 1,000 mL to infuse over 10 hours = 100 mL/L.

Question 23

23. A patient is going to have bowel surgery in the morning. The physician orders 500 mL of GoLytely PO to be administered at 5 PM this evening. How many liters will the nurse administer?

A) 1
B) 3⁄4
C) 1⁄2
D) 1⁄4

Answer 23

Ans: C Feedback:
1L = X 1,000 500 mL
Cross-multiply to learn 500 mL = 1⁄2 or 0.5 L.

Question 24

24. The patient returns from the postanesthesia care unit (PACU) with the following order: morphine 3 mg IV every 2 hours as needed for relief of pain. The vial reads morphine, 4 mg/mL. How many milliliters of morphine will the nurse administer?

A) 1 mL
B) 0.75 mL
C) 0.5 mL
D) 0.25 mL

Answer 24

Ans: B Feedback:

Using the figures from this problem: 4 mg/1 mL = 3 mg/X. Cross-multiply yielding 0.75 mL.

Question 25

25. A patient is admitted with a deep vein thrombosis in his or her left calf. The physician orders Heparin, 7,500 units subcutaneously every 12 hours. The medication vial reads Heparin, 10,000 units/mL. How many milliliters does the nurse administer?

A) 0.5 mL
B) 0.75 mL
C) 1 mL
D) 1.25 mL

Answer 25

Ans: A Feedback:
Using the information supplied by the problem: 10,000 units/1 mL = 7,500/X. Cross-multiplying yields X = 0.75 mL for each dose.

Question 26

26. A patient with an acute myocardial infarction is admitted to the coronary care unit. The physician has ordered heparin 25,000 units in 250 mL normal saline to infuse at a rate of 600 units/h. The nurse sets the infusion pump to deliver how many milliliters in an hour?

A) 8
B) 7
C) 6
D) 5

Answer 26

Ans: C
Feedback:
First determine the number of units per mL = 25,000 units/250 mL = 100 units/1 mL. Next use the ratio and proportion method to determine the number of milliliters needed to supply 600 units/h. 100 units/1 mL = 600 units/X. Cross-multiplying yields 6 mL needed every hour to supply the required dose.

Question 27

27. The physician has ordered 30 mg of Demerol IM for relief of a severe migraine headache. The package insert reads meperidine hydrochloride (Demerol) 50 mg/mL. How many milliliters would the nurse administer?

A) 1.6
B) 1
C) 0.6
D) 0.5

Answer 27

Ans: C Feedback:
Filling in the information from the problem: 50 mg/1 mL = 30 mg/X mL. Cross-multiply yielding 0.6 mL required to administer a 30-mg dosage.

Question 28

28. A patient is experiencing pain, so the physician orders codeine 1⁄2 grain every 4 hours. How many milligrams of codeine would the nurse administer?

A) 15 mg
B) 30 mg
C) 60 mg
D) 120 mg

Answer 28

Ans: B
Feedback:
The simplest way to convert measurements from one system to another is to set up a ratio and proportion equation. The ratio containing two known equivalent amounts is placed on one side of an equation, and the ratio containing the amount you wish to convert and its unknown equivalent is placed on the other side.
60 mg/1 grain = flexion range of motion. Cross-multiplying yields 30 mg.

Question 29

29. A 79-year-old female patient presents at the clinic complaining of constipation for 1 week. The nurse practitioner prescribes Milk of Magnesia 2 teaspoons by mouth as needed for relief of constipation. How many milliliter will the nurse administer?

A) 30 mL
B) 7.5 mL
C) 10 mL
D) 15 mL

Answer 29

Ans: C
Feedback:
Use the ratio and proportion method to convert from household system to metric system. 5 mL/1 tsp = X mL/2 tsp. Cross-multiplying yields 10 mL = 2 tsp.

Question 30

30. A patient has orders to receive 3,000 mL of IV fluid at a rate of 150 mL/h. If the infusion starts at 08:00, when would it be finished?

A) 20:00
B) 23:00
C) 01:00
D) 04:00

Answer 30

Ans: D Feedback:
Amount of fluid to infuse = 3,000 mL; rate of infusion = 150 mL. 3,000 ÷ 150 mL = 20 hours to infuse. There are 24 hours in a day – 20 hours = 4 hours. The infusion will complete in 4 hours before 08:00 (08:00 – 04:00 = 04:00 hour) so the infusion completes at 04:00.

Question 31

31. The nurse recognizes that what system is being used when seeing a medication ordered in minims?

A) Apothecary
B) Metric
C) Household
D) Avoirdupois

Answer 31

Ans: A Feedback:
The apothecary system used minims as the basic measure of liquid and is rarely used today. The metric system uses liters as the basic unit of measurement for fluid, while the household system uses ounces and the avoirdupois system uses ounces with a different conversion amount.

Question 32

32. The nurse is calculating the patient’s intake and output record and converts ounces to milliliters. What systems is this nurse converting from and to?

A) From household to metric
B) From metric to household
C) From household to apothecary
D) From apothecary to Avoirdupois

Answer 32

Ans: A
Feedback:
Ounces can be either household or Avoirdupois, although they are not equal measurements and milliliters is a metric measurement. Since Avoirdupois to metric is not an available choice, the correct answer is household to metric.

Question 33

33. What is the most accurate method for the nurse to use when determining a pediatric dosage?

A) A nomogram using body surface area
B) Young’s rule
C) Fried’s rule
D) Clark’s rule

Answer 33

Ans: A
Feedback:
The most accurate means of determining a pediatric drug dosage is a nomogram using body surface area because the weight and body surface area of two children who are of the same age can be significantly different. Young’s rule, Fried’s rule, and Clark’s rule are based on the child’s age and the usual adult dosage and are rarely used today unless no other method will suffice for a specific drug.

Question 34

34. The nurse determines a child’s body surface area is 0.4 m2 and the average adult dosage of the medication is 500 mg. The medication is supplied in liquid form with 500mg/5 mL. How many milliliter will the nurse administer?

A) 3.46 mL
B) 1.73 mL
C) 0.5 mL
D) 12 mL

Answer 34

Ans: A
Feedback: 2 The formula for calculating the child’s dose using body surface area is surface area in m divided by 1.73 and then multiplied by adult dosage. Using the information supplied in this problem (0.4 ÷ 1.73) × 500 mg = 346 mg. Using the ratio and proportion method, 500 mg/5 mL = 346 mg/X mL; cross-multiplying yields 3.46 mL for the nurse to administer.

Question 35

35. The physician orders acetaminophen (Tylenol) 15 mg/kg q4 hours PRN (as needed) for pain. The drug is supplied with 160 mg/5 mL. The infant weighs 12 pounds. How many milliliter of medication will the nurse administer?

A) 2.5 mL
B) 5.6 mL
C) 12.4 mL
D) 10.7 mL

Answer 35

Ans: A
Feedback:
Begin by converting the infant’s weight to kilograms (12 pounds ÷ 2.2 pounds/kg = 5.45 kg). The order says to give 15 mg/kg. To determine this child’s dosage multiply weight and 15 mg/kg (5.45 kg × 15 mg/kg = 81.75 mg/dose). Finally, use the ratio and proportion method to calculate how to prepare the medication: 160 mg/5 mL = 81.75 mg/X mL; cross-multiplying yields 2.5 mL.