Drug Dosage Calculations NCLEX Practice Questions (100+ Items)

Math in nursing!

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Welcome to your NCLEX reviewer for drug calculations! In this nursing test bank, practice dosage calculation problems to measure your competence in nursing math. As a nurse, you must be able to accurately and precisely calculate medication dosages to provide safe and effective nursing care. The goal of this quiz is to help students and registered nurses alike to grasp and master the concepts of medication calculation.


Drug Dosage Calculation Practice Quiz

In this section are the practice problems and questions for drug dosage calculations. This nursing test bank set includes 100+ questions broken down into four parts. Included topics are dosage calculation, metric conversions, unit conversions, parenteral medications, and fluid input and output. As you can tell, this NCLEX practice exam requires tons of calculations, so get your calculators ready!

Remember to answer these questions at your own pace and don’t forget to read the rationales! Don’t be discouraged if you have incorrect answers, you are here to learn! Make sense of the rationales and review the drug dosage calculations study guide below.

Quizzes included in this guide are:

Guidelines

  • Read and understand each question before choosing the best answer. 
  • Since this is a review, answers and rationales are shown after you click on the "Check" button. 
  • There is no time limit, answer the questions at your own pace. 
  • Once all questions are answered, you'll be prompted to click the "Quiz Summary" button where you'll be shown the questions you've answered or placed under "Review". Click on the "Finish Quiz" button to show your rating. 
  • After the quiz, please make sure to read the questions and rationales again by click on the "View Questions" button. 
  • Comment us your thoughts, scores, ratings, and questions about the quiz in the comments section below!
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Part 2: Oral Medications Dosage Calculations Practice Quiz (40 Items)

All practice questions in this section are related to dosage calculations for oral medications. Don’t forget to read the rationales!

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Drug Calculations Reviewer for Nurses

This is your study guide to help you refresh or review what you know about drug dosage calculations including tips on how to answer them.

NCLEX Tips for Dosage Calculation Questions

  • The fill-in-the-blank question format is usually used for medication calculation, IV flow rate calculation, or determining the intake-output of a client. In this question format, you’ll be asked to perform a calculation and type in your answer in the blank space provided. 
  • Always follow the specific directions as noted on the screen. 
  • The unit of measure you need for your final answer is always given. 
  • There will be an on-screen calculator on the computer for you to use. 
  • Do not put any words, units of measurements, commas, or spaces with your answer, type only the number. Only the number goes into the box. Rounding an answer should be done at the end of the calculation or as what the question specified, and if necessary, type in the decimal point.

Nursing Responsibilities for Medication Administration

  • 10 Rights of Medication Administration. Understanding the 10 Rights of Drug Administration can help prevent many medication errors. Nurses, who are primarily involved in the administration of medications, benefit from this simplified memory aid to help guide them to administer medications safely.
    • Right Drug. The first right of drug administration is to check and verify if it’s the right name and form. Beware of look-alike and sound-alike medication names. Misreading medication names that look similar is a common mistake. These look-alike medication names may also sound alike and can lead to errors associated with verbal prescriptions. Check out The Joint Commission’s list of look-alike/sound-alike drugs.
    • Right Patient. Ask the name of the client and check his/her ID band before giving the medication. Even if you know that patient’s name, you still need to ask just to verify. 
    • Right Dose. Check the medication sheet and the doctor’s order before medicating. Be aware of the difference between an adult and a pediatric dose. 
    • Right Route. Check and verify the order (i.e., per orem, IV, SQ, IM)
    • Right Time and Frequency. Check the order for when it would be given and when was the last time it was given. 
    • Right Documentation. Make sure to write the time and any remarks on the chart correctly. 
    • Right History and Assessment. Secure a copy of the client’s history to drug interactions and allergies. 
    • Right Drug Approach and Right to Refuse. Give the client enough autonomy to refuse the medication after thoroughly explaining the effects. 
    • Right Drug-Drug Interaction and Evaluation. Review any medications previously given or the diet of the patient that can yield a bad interaction to the drug to be given. Check also the expiry date of the medication being given. 
    • Right Education and Information. Provide enough knowledge to the patient of what drug he/she would be taking and what are the expected therapeutic and side effects.

Systems of Measurement

  • There are three systems of measurement used in nursing: the metric system, the apothecaries’ system, and household system. 
  • Metric System
    • The most widely used international system of measurement.
    • The basic units of metric measures are the gram (weight), meter (length or distance), and liter (volume).
    • It is a decimal-based system that is logically organized into units of 10. Basic units are multiplied or divided by 10 to form secondary units. 
  • Apothecaries’ System
    • The apothecaries’ system is one of the oldest systems of measurement, older than the metric system and is considered to be out of date. 
    • The basic units used in this system are the grain (gr) for weight, minim for volume, ounce, and pound. All of which are seldomly used in the clinical setting. 
    • Quantities in the apothecaries’ system are often expressed by lowercase Roman numerals when the unit of measure is abbreviated. And the unit of measure precedes the quantity. Quantities less than 1 are expressed as fractions. Examples: “gr ii”, “gr ¼ ”
    • And yes, it can be confusing therefore use the metric system instead to avoid medication errors.
  • Household System
    • Household system measures may be used when more accurate systems of measure are not required. 
    • Included units are drops, teaspoons, tablespoons, cups, pint, and glasses.
  • Other Systems of Measurement
    • Milliequivalent (mEq)
      • The milliequivalent is an expression of the number of grams of a medication contained in 1 milligram of a solution.
      • Examples: the measure of serum sodium, serum potassium, and sodium bicarbonate is given in milliequivalents.
    • Unit (U)
      • Unit measures a medication in terms of its action, not its physical weight. 
      • When documenting, do not write “U” for unit, rather spell it as “unit” as it is often mistaken as “0”. 
      • Examples: Insulin, penicillin, and heparin sodium are measured in units.

Converting Units of Weight and Measure

  • Converting values between metric system
    • For drug dosages, the metric units used are the gram (g), milligram (mg), and microgram (mcg). For volume units milliliters (mL) and liters (L). 
    • It is simple to compute for equivalents using the metric system. It can be done by dividing or multiplying; or by moving the decimal point three places to the left or right. 
    • Do not use a “trailing zero” after the decimal point when the dosage is expressed as a whole number. For example, if the dosage is 2m mg, do not insert a decimal point or the trailing zero as this could be mistaken for “20” if the decimal point is not seen. 
    • On the other hand, do not leave a “naked” decimal point. If a number begins with a decimal, it should be written with a zero and a decimal point before it. For example, if the dosage is 2/10 of a milligram, it should be written as 0.2 mg. It could be mistaken for 2 instead of 0.2. 
UnitEquivalents
Metric systemEquivalents
1 microgram (mcg)0.000001 g
1 milligram (mg)0.0001 g or 1000 mcg
1 gram (g)1000 mg
1 kilogram (kg)1000 g
1 kilogram (kg)2.2 lbs
1 milliliter (mL)0.001 L
Apothecary system (weight)Equivalents
1 grain (gr)60 or 65 mg
5 grain (gr)300 or 325 mg
15 grain (gr)1000 mg or 1g
1/150 grain (gr)0.4 mg
Household system (volume)Equivalents
1 teaspoon (tsp)5 ml or 16 drops
1 tablespoon (T)3 teaspoons or 15 mL
1 fluid ounce (fl oz)2 tablespoons or 30 mL
1 cup (C)8 fluid oz or 240 mL
1 pint (pt) 16 fluid oz or 480 mL
1 quart (qt)2 pints or 946 mL or 32 fl oz
Household system (weight)Equivalents
1 pound (lb)16 ounce
2.2 pounds (lbs)1 kilogram
  • Converting Units Between Systems
    • Household and metric measures are equivalent and not equal measures.
    • Conversions to equivalent measures between systems is necessary when a medication prescription is written in one system but the medication label is stated in another.
    • Medications are not always prescribed and prepared in the same system of measurement; therefore conversion of units from one system to another is necessary.
    • Common conversions in the healthcare setting include pound to kilograms, milligrams to grains, minims to drops. 

Methods for Drug Dosage Calculations

  • Standard Method
    • The commonly used formula for calculating drug dosages. 
    • Where in:
      • D = Desired dose or dose ordered by the primary care provider. 
      • H = dose on hand or dose on the label of bottle, vial, ampule.
      • V = vehicle or the form in which the drug comes (i.e., tablet or liquid). 

STANDARD FORMULA

Formula = \frac{Desired (D) \times Vehicle (V) }{On\ Hand (H)} = amount \ to \ administer

Example:
Order: Acetaminophen 500 mg
On hand: Acetaminophen 250 mg in 5 mL

Desired (D) = 500 mg
On hand (H) = 250 mg
Vehicle (V) = 5 mL

Computation:

\frac{500\ mg}{250\ mg}  \times 5\ mL = 10\ mL

Answer: 10 mL

  • Ratio and Proportion Method
    • Considered as the oldest method used for drug calcluation problems.
    • For the equation, the known quantities are on the left side, while the desired dose and the unknown amount to administer are on the right side.
    • Where in:
      • D = Desired dose or dose ordered by the primary care provider. 
      • H = dose on hand or dose on the label of bottle, vial, ampule.
      • V = vehicle or the form in which the drug comes (i.e., tablet or liquid). 
      • X = amount to administer
    • Once the equation is set up, multiply the extremes (H and x) and the means (V and D). Then solve for x.

RATIO AND PROPORTION METHOD

H : V = D : x

Example:
Order: Erythromycin 750 mg
On hand: Erythromycin 250 mg capsules

Desired (D) = 750 mg
On hand (H) = 250 mg
Vehicle (V) = 1 capsule

Computation:
250 (H) : 1 (V) = 750 (D) : x

Multiply the extremes and the means:

250x = 750
x=3 capsules

Answer: 3 capsules


  • Fractional Equation Method
    • A method similar to ratio and proportion but expressed as fractions.
    • Where in:
      • D = Desired dose or dose ordered by the primary care provider. 
      • H = dose on hand or dose on the label of bottle, vial, ampule.
      • V = vehicle or the form in which the drug comes (i.e., tablet or liquid). 

FRACTIONAL EQUATION METHOD

\frac{H}{V}= \frac{D}{x}

Example:
Order: Digoxin 0.25 mg
On hand: Digoxin 0.125 mg tablets

Desired (D) = 0.25 mg
On hand (H) = 0.125 mg
Vehicle (V) = 1 tablets

Computation:

\frac{0.125\ mg}{1\ tablets}= \frac{0.25\ mg}{x}


Answer: 2 tablets


  • Fluid Intake and Output Calculation
    • Intake and output (I&O) measurement and recording is usually done to monitor a client’s fluid and electrolyte balance during a 24-hour period. 
    • Intake and output is done for patients with increased risk for fluid and electrolyte imbalance (e.g., heart failure, kidney failure). 
    • Unit used in measurement of I&O is milliliter (mL)
    • Measuring fluid intake entails recording each item of fluid consumed or administered, all of the following fluids are recorded: 
      • Oral fluids (e.g., water, juice, milk, soup, water taken with medication). 
      • Liquid foods at room temperature (e.g., ice cream, gelatin, custard). 
      • Tube feedings including the water used for flushes. 
      • Parenteral fluids
      • Blood products
      • IV medications
    • Measurement of fluid output includes: 
      • Urinary output
      • Vomitus
      • Liquid feces
      • Tube drainage
      • Wound and fistula drainage
    • Measurement of fluid input and output are totaled at the end of the shift and documented in the patient’s chart. 
    • Determine if fluid intake and fluid output are proportional. When there is a significant discrepancy between intake and output, report to the primary care provider.

Recommended Links

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Paul Martin is a registered nurse with a bachelor of science in nursing since 2007. Having worked as a medical-surgical nurse for five years, he handled different kinds of patients and learned how to provide individualized care to them. Now, his experiences working in the hospital is carried over to his writings to help aspiring students achieve their goals. He is currently working as a nursing instructor and have a particular interest in nursing management, emergency care, critical care, infection control, and public health. As a writer at Nurseslabs, his goal is to impart his clinical knowledge and skills to students and nurses helping them become the best version of themselves and ultimately make an impact in uplifting the nursing profession.

4 COMMENTS

  1. Wondering why on number 8 it was multiplied by 1, the question says 10 ml, not 1, so my answer was 8.78 ml? Is this one wrong, or am I wrong? My formula has me dividing 4,390 units by 5,000 units, then taking that answer, which was 0.878, and multiplying by the ml quantity, which was 10, so I ended up with 8.78, which could be rounded to 8.8 ml. Have I missed something or is this question/work/answer incorrect? I’m studying for my dosage calculation exam and hoping to hear from you soon. Thank you for your time.

  2. The description of the author is riddled with so many grammatical errors, it makes me cringe. I hope he didn’t write it himself because it makes him look bad! Being a nurse and having a bachelors degree, you’d think basic grammar knowledge would be implied. Unless English isn’t a first language, then I can forgive the numerous mistakes. Uhg. Let me know if you want me to edit it. I will gladly fix the errors.

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