Math for Medication Administration

15 Calculating Medication Doses Based on Weight

Lesson

Learning Outcomes

By the end of this chapter, learners will be able to:

  • calculate medication doses when the quantity is based on client weight,
  • calculate minimum and maximum medication doses when the quantity is based on client weight and a dose range is given, and
  • verify safe doses for weight based medication recommendations.

Calculating Weight Based Doses

Some medications require the dose to be determined based on the weight of the client. Orders are written indicating how much medication should be given for each kilogram (kg) the client weighs. You will need to calculate this amount to ensure you are administering the correct amount to the client. You may see weight based orders written in different ways, for example:

morphine 0.2 mg/kg po q4h

morphine 0.1 – 0.5 mg/kg po q4h

Note in the first example only one dose will be calculated, whereas in the second example there is a range of doses which are possible. If the client’s weight has been recorded in pounds or ounces, you must convert the client’s weight into kilograms or grams, as weight based drug dosages are always given in an amount per kilogram or gram (for some neonatal dosages). When a range is given in the order, you will calculate the smallest and largest amounts which can be given, based on the client’s weight.

Sample Exercise 15.1

An order is written for a child to receive 0.2 mg/kg of morphine PO q4h prn. The child weighs 14 kg. Calculate the prn dose for this child.

Answer:

[latex]x\text{ mg}=\dfrac{\text{0.2 mg}}{1\cancel{\text{kg}}}\times14\cancel{\text{kg}}[/latex]

[latex]x\text{ mg}=\dfrac{\text{2.8 mg}}{1}[/latex]

[latex]\text{ mg}=\text{2.8}[/latex]

Sample Exercise 15.2

An order is written for a child to receive morphine 0.1 – 0.5 mg/kg PO q4h prn. The child weighs 24 kg. Calculate the range of prn doses for this child.

Answer:

The range is 2.4-12 mg of morphine per dose. These represent the smallest and largest doses the child should receive.

[latex]x\text{ mg}=\dfrac{\text{0.1 mg}}{1\cancel{\text{kg}}}\times24\cancel{\text{kg}}[/latex]

[latex]x\text{ mg}=\dfrac{\text{2.4 mg}}{1}[/latex]

[latex]\text{ mg}=\text{2.4}[/latex]

[latex]x\text{ mg}=\dfrac{\text{0.5 mg}}{1\cancel{\text{kg}}}\times24\cancel{\text{kg}}[/latex]

[latex]x\text{ mg}=\dfrac{\text{12 mg}}{1}[/latex]

[latex]\text{ mg}=12[/latex]

You might have noticed there is a step we can take out of the calculation above. Whenever we are calculating a dose where the amount per dose and the weight of the client have the same unit for weight, the following formula can be used:

[latex]\text{ mg}=\text{amount per dose}\times\text{weight of client}[/latex]

Sample Exercise 15.3

An order is written for a child to receive 25 mg/kg of cephazolin IV q12h. The child weighs 37 kg. Calculate the dose for this child.

Answer:

[latex]\text{ mg}=\text{amount per dose}\times\text{weight of client}[/latex]

[latex]\text{ mg}=\text{25}\times\text{37}[/latex]

[latex]\text{ mg}=\text{925}[/latex]

Verifying Dosage Safety

Recommended Dosage

To verify if a medication dose is safe for a client, the ordered dose must be compared with the recommended dosage information published by the manufacturer or within a reference manual (drug guide, pharmacy documents, etc).
You will need to read carefully to ensure you are following the recommendations for categories relevant to your client, as there may be recommended dosages for multiple circumstances. For instance, the type of client (often based on age and/or weight) or the reason the medication is being prescribed for.

Sample Recommended Dose

The World Health Organization recommends the following dosage options for children ages 2 months to 12 years:

Meropenem 60 mg/kg/day IV divided in 3 doses

or

Meropenem 120 mg/kg/day IV divided in 3 doses (in severe infection)

In this example, the difference in the two doses is related to the reason the medication being administered for.

Antibiotic Dosing for Children: Draft expert Recommendations for the 2017 Essential Medicines List for Children (EMLc) [PDF]

Critical Thinking Questions

  1. What is the risk to the client if the dose is higher than the recommended range?
  2. What is the risk to the client if the dose is lower than the recommended range?
Answers:
  1. There is risk of the client receiving a toxic dose if a dose of the medication is given above the recommended range. Adverse reactions may also worsen or occur, with the severity depending on the amount of extra medication.
  2. There is risk of the medication not having any, or reduced effect. The client’s condition could worsen.

Safe Dosage for Weight Based Medications

In order to determine if the ordered dose is appropriate for the client, you need to compare the medication order to the information in the reference guide. Often, the recommended dose is given as a total daily amount with a range of possible frequencies, rather than the amount for a single dose. If this is the case, you will need to calculate the recommended doses for the low and high end of the range. It is important you ensure you are using the right information from the drug reference manual when determining which numbers to use in your calculations. You will determine which information is important by referring back to the information about the client. Relevant information may include:

  • client age
  • client weight
  • route
  • frequency
  • reason
  • presence of kidney or liver disease
  • pregnancy status
  • other diagnostic results

Determine if the following medication order is safe:

vancomycin 500 mg IV q12h

Drug guide information: vancomycin
Children: 
IV: 10-15 mg/kg q6-12h
PO: 40 mg/kg
Adults:
IV: 500-2,000mg q12-24h
PO: 125-500 mg q6-8h

Client information:
11 year old with severe staphylococcal infection, weight 38kg

To solve the problem: 
Step 1: Determine which information in the drug guide is relevant to the client.
In this case, the relevant information is IV: 10-15 mg/kg q6-12h
This is the dose for the age of the client and matches the route in the medication order.
Step 2: Calculate the minimum and maximum recommended doses.

[latex]\text{min dose}=\dfrac{\text{10 mg}}{1\cancel{\text{kg}}}\times38\cancel{\text{kg}}=380 \text{ mg}[/latex]
[latex]\text{max dose}=\dfrac{\text{15 mg}}{1\cancel{\text{kg}}}\times38\cancel{\text{kg}}=570 \text{ mg}[/latex]

Step 3: Compare the dose in the order to the minimum and maximum recommended doses. Does the dose fall between these numbers? Yes, 500 mg falls between 380 and 570mg.

Sample Exercise 15.4

Order: amoxicillin 250 mg PO TID

Reference manual states: Safe dosage is 20 to 40 mg/kg/day

Client weighs: 20 kg

Problem: Based on the client’s weight, is this a safe dose?

Answer:

Yes, this is a safe dose. 250 mg is in the safe range of 133-267 mg per dose.
Since the reference manual gives you a total daily amount, you must calculate the total daily range first, then divide by the order frequency to see if the dose is safe.

[latex]\text{min daily amount}=\dfrac{\text{20 mg}}{\text{1 kg}}\times\text{20 kg}=\text{400 mg}\\[/latex][latex]\text{max daily amount}=\dfrac{\text{40 mg}}{\text{1 kg}}\times\text{20 kg}=\text{800 mg}\\[/latex][latex]\text{min dose}=\dfrac{\text{400 mg}}{\text{1 day}}\times\dfrac{\text{1 day}}{\text{3 doses}}=\text{133 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{800 mg}}{\text{1 day}}\times\dfrac{\text{1 day}}{\text{3 doses}}=\text{267 mg/dose}[/latex]

Administering Doses from a Range

When a weight based medication order includes a range of dose options, you will need to use critical thinking to determine what dose of medication to give after completing a thorough assessment with the client.

Critical Thinking Questions

What factors might impact the dose you choose to give?

Answer:

You may need to consider factors such as:

  • has the client has received this medication before?
  • if given previously, was the medication effective when it was last given?
  • does the client experience adverse effects with this medication?
  • are there other diagnostic tests you need to review when selecting the dose (creatinine, INR, ptt, etc.)?
  • what is the patient’s preference?

As a novice student, you will make decisions about what particular dose to give in partnership with the client’s primary nurse and/or your nursing instructor.

Practice Set 15.1: Calculating weight based doses

Practice Set 15.1: Calculating weight based doses

Calculate the dose for each of the following medication orders:

  1. vancomycin 15 mg/kg IV TID, child weighs 32 kg
  2. nitrofurantoin 1mg/kg PO q6h, child weighs 44 lb
  3. acetaminophen 10-15 mg/kg PO q4h prn, child weighs 16 kg
  4. piperacillin-tazobactam 90mg/kg IV q8h, child weighs 27 kg
  5. ibuprofen 4-10 mg/kg PO q4-6h prn, child weighs 19 kg
  6. clindamycin 2-5 mg/kg PO q6h, child weighs 17 kg
  7. meropenem 20 mg/kg IV q8h, child weighs 38.5 lb
  8. clarithromycin 7.5mg/kg PO BID, child weighs 12 kg
  9. cefotaxime 50 mg/kg IV q8h, child weighs 36 kg
  10. ketorlac 0.5 mg/kg IV q6-8h prn, child weighs 70 kg
Answers:
  1. 480 mg/dose          [latex]\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{32 kg}[/latex]
  2. 20 mg/dose            [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{44 lbs}=\text{20 kg}[/latex],  [latex]\text{dose}=\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{20 kg}[/latex]
  3. 160-240 mg/dose  [latex]\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{16 kg}[/latex], [latex]\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{16 kg}[/latex]
  4. 2430 mg/dose       [latex]\dfrac{\text{90 mg}}{\text{1 kg}}\times\text{27 kg}[/latex]
  5. 76-190 mg/dose    [latex]\dfrac{\text{4 mg}}{\text{1 kg}}\times\text{19 kg}[/latex], [latex]\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{19 kg}[/latex]
  6. 34-85 mg/dose     [latex]\dfrac{\text{2 mg}}{\text{1 kg}}\times\text{17 kg}[/latex], [latex]\dfrac{\text{5 mg}}{\text{1 kg}}\times\text{17 kg}[/latex]
  7. 350 mg/dose        [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{38.5 lbs}=\text{17.5 kg}[/latex], [latex]\text{dose }=\dfrac{\text{20 mg}}{\text{1 kg}}\times\text{17.5 kg}[/latex]
  8. 90 mg/dose          [latex]\dfrac{\text{7.5 mg}}{\text{1 kg}}\times\text{12 kg}[/latex]
  9. 1800 mg/dose     [latex]\dfrac{\text{50 mg}}{\text{1 kg}}\times\text{36 kg}[/latex]
  10. 35 mg/dose          [latex]\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{70 kg}[/latex]

Practice Set 15.2: Calculating weight based doses

Practice Set 15.2: Calculating weight based doses

Calculate the dose for each of the following medication orders:

  1. amoxicillin 50 mg/kg PO BID, child weighs 43 kg
  2. diphenhydramine 1-2 mg/kg IM q4-8h prn, child weighs 15 kg
  3. cephalexin 12.5 mg/kg PO q6h, child weighs 23 kg
  4. ketorlac 0.5 mg/kg IV q6-8h prn, child weighs 47 lb
  5. ciprofloxacin 15 mg/kg PO q12h, child weighs 31 kg
  6. acetaminophen 10-15 mg/kg PO q4h prn, child weighs 35 kg
  7. ceftriaxone 80 mg/kg IV once daily, child weighs 92 lb
  8. gentamycin 7 mg/kg IV once daily, child weighs 29 kg
  9. dimenhydrinate 12.5-25 mg/kg PO q6-8h prn, child weighs 73 lb
  10. codeine 0.5-1 mg/kg q4-6h PO prn, child weighs 19 kg
Answers:
  1. 2150 mg/dose              [latex]\dfrac{\text{50 mg}}{\text{1 kg}}\times\text{43 kg}[/latex]
  2. 15 – 30 mg/dose          [latex]\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{15 kg}[/latex], [latex]\dfrac{\text{2 mg}}{\text{1 kg}}\times\text{15 kg}[/latex]
  3. 287.5 mg/dose          [latex]\dfrac{\text{12.5 mg}}{\text{1 kg}}\times\text{23 kg}[/latex]
  4. 10.7 mg/dose            [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{47 lbs}=\text{21.4 kg}[/latex],  [latex]\text{dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{21.4 kg}[/latex]
  5. 465 mg/dose              [latex]\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{31 kg}[/latex]
  6. 350 – 525 mg/dose      [latex]\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{35 kg}[/latex], [latex]\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{35 kg}[/latex]
  7. 3344 mg/dose             [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{92 lbs}=\text{41.8 kg}[/latex],  [latex]\text{dose}=\dfrac{\text{80 mg}}{\text{1 kg}}\times\text{41.8 kg}[/latex]
  8. 203 mg/dose            [latex]\dfrac{\text{7 mg}}{\text{1 kg}}\times\text{29 kg}[/latex]
  9. 415 – 830 mg/dose       [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{73 lbs}=\text{33.2 kg}[/latex],  [latex]\text{dose}=\dfrac{\text{12.5 mg}}{\text{1 kg}}\times\text{33.2 kg}[/latex], [latex]\text{dose}=\dfrac{\text{25 mg}}{\text{1 kg}}\times\text{33.2 kg}[/latex]
  10. 9.5 – 19 mg/dose      [latex]\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{19 kg}[/latex], [latex]\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{19 kg}[/latex]

Practice Set 15.3: Calculating weight based doses

Practice Set 15.3: Calculating weight based doses

Calculate the dose for each of the following medication orders:

  1. atropine 0.02 mg/kg/dose IV Q5 min x 2 doses prn, child weighs 15 kg
  2. morphine 0.08 mg/kg/dose PO Q3-4H PRN, child weighs 22 lbs
  3. naproxen 7 mg/kg/dose PO Q8-12H, child weighs 82 lbs
  4. digoxin 10 mcg/kg/24 hr PO once daily, child weighs 31 lbs
  5. octreotide 2 mcg/kg/dose IV bolus over 2-5 min, child weighs 25 kgs
  6. adenosine initial dose 0.1 mg/kg rapid IV within 1-2 sec, child weighs 16 lbs
  7. meropenem 20 mg/kg/dose IV Q8H, child weighs 13 kgs
  8. prednisone 0.25 mg/kg/dose PO BID, child weighs 48 lbs
  9. piperacillin-tazobactam 75 mg/kg/dose IV Q6H, child weighs 24 kg
  10. norepinephrine 0.1 mcg/kg/min, child weighs 14 kgs
Answers:
  1. 0.3 mg/dose
    [latex]\dfrac{\text{0.02 mg}}{\text{1 kg}}\times\text{15 kg} = \text{0.3 mg/dose}[/latex]
  2. 0.79 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{22 lbs} = \text{9.97 kg}[/latex][latex]\dfrac{\text{0.08 mg}}{\text{1 kg}}\times\text{9.97 kg} = \text{0.79 mg/dose}[/latex]
  3. 260 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{82 lbs} = \text{37.19 kg}[/latex][latex]\dfrac{\text{7 mg}}{\text{1 kg}}\times\text{37.19 kg} = \text{260 mg/dose}[/latex]
  4. 140.1 mcg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{31 lbs} = \text{14.01 kg}[/latex][latex]\dfrac{\text{10 mcg}}{\text{1 kg}}\times\text{14.01 kg} = \text{140.1 mcg/dose}[/latex]
  5. 50 mcg/dose
    [latex]\dfrac{\text{2 mcg}}{\text{1 kg}}\times\text{25 kg} = \text{50 mcg/dose}[/latex]
  6. 0.73 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 kgs}}\times\text{16 lbs} = \text{7.25 kg}[/latex][latex]\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{7.25 kg} = \text{0.73 mg/dose}[/latex]
  7. 260 mg/dose
    [latex]\dfrac{\text{20 mg}}{\text{1 kg}}\times\text{13 kg} = \text{260 mg/dose}[/latex]
  8. 5.45 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{48 lbs} = \text{21.8 kg}[/latex][latex]\dfrac{\text{0.25 mg}}{\text{1 kg}}\times\text{21.8 kg} = \text{5.45 mg/dose}[/latex]
  9. 1800 mg/dose
    [latex]\dfrac{\text{75 mg}}{\text{1 kg}}\times\text{24 kg} = \text{1800 mg/dose}[/latex]
  10. 1.4 mcg/min
    [latex]\dfrac{\text{0.1 mcg}}{\text{1 kg}}\times\text{14 kg} = \text{1.4 mcg/min}[/latex]

Practice Set 15.4: Calculating weight based doses with ranges

Practice Set 15.4: Calculating weight based doses with ranges

Calculate the dose for each of the following medication orders:

  1. amoxicillin/clavulanic acid 10-15 mg/kg/dose PO TID, child weighs 39 kg
  2. cefazolin 35–50 mg/kg/dose IV Q8H, child weighs 48 kg
  3. clopidogrel 0.2-1 mg/kg/dose PO once daily, child weighs 27 lbs
  4. haloperidol 0.01-0.02 mg/kg/dose PO BID, child weighs 84 lbs
  5. diazepam 0.04-0.2 mg/kg/dose PO Q6-8H, child weighs 37 kg
  6. ibuprofen 5-10 mg/kg/dose PO Q6-8H, child weighs 72 lbs
  7. ketorolac 0.2-0.5 mg/kg/dose IV/IM Q6-8H PRN, child weighs 49 kg
  8. metoprolol 0.5-1 mg/kg/dose PO BID, child weighs 49 lbs
  9. mannitol 0.25-1 g/kg IV over 20-30 min repeat Q4-8H PRN, child weighs 33 lbs
  10. spironolactone 1-1.5 mg/kg/dose BID, child weighs 83 lbs
Answers:
  1. 390-585 mg/dose
    [latex]\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{39 kg} = \text{390 mg/dose}\\[/latex][latex]\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{39 kg} = \text{585 mg/dose}[/latex]
  2. 1680-2400 mg/dose
    [latex]\dfrac{\text{35 mg}}{\text{1 kg}}\times\text{48 kg} = \text{1680 mg/dose}\\[/latex][latex]\dfrac{\text{50 mg}}{\text{1 kg}}\times\text{48 kg} = \text {2400 mg/dose}[/latex]
  3. 2.45-12.25 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{27 lbs} = \text{12.25 kg}\\[/latex][latex]\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{12.25 kg} = \text{2.45 mg/dose}\\[/latex][latex]\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{12.25} = \text{12.25 mg/dose}[/latex]
  4. 0.38-0.76 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{84 lbs} = \text{38.1 kg}\\[/latex][latex]\dfrac{\text{0.01 mg}}{\text{1 kg}}\times\text{38.1 kg} = \text{0.38 mg/dose}\\[/latex][latex]\dfrac{\text{0.02 mg}}{\text{1 kg}}\times\text{38.1 kg} = \text{0.76 mg/dose}[/latex]
  5. 1.48-7.4 mg/dose
    [latex]\dfrac{\text{0.04 mg}}{\text{1 kg}}\times\text{37 kg} = \text{1.48 mg/dose}\\[/latex][latex]\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{37 kg} = \text{7.4 mg/dose}[/latex]
  6. 163.3-326.6 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{72 lbs} = \text{32.66 kg}\\[/latex][latex]\dfrac{\text{5 mg}}{\text{1 kg}}\times\text{32.66 kg} = \text{163.3 mg/dose}\\[/latex][latex]\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{32.66 kg} = \text{326.6 mg/dose}[/latex]
  7. 9.8-24.5 mg/dose
    [latex]\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{49 kg} = \text{9.8 mg/dose}\\[/latex][latex]\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{49 kg} = \text{24.5 mg/dose}[/latex]
  8. 11.15-22.3 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{49 lbs} = \text{22.3 kg}\\[/latex][latex]\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{22.3 kg} = \text{11.15 mg/dose}\\[/latex][latex]\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{22.3 kg} = \text{22.3 mg/dose}[/latex]
  9. 3.75-15 g/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{33 lbs} = \text{15 kg}\\[/latex][latex]\dfrac{\text{0.25 g}}{\text{1 kg}}\times\text{15 kg} = \text{3.75 g/dose}\\[/latex][latex]\dfrac{\text{1 g}}{\text{1 kg}}\times\text{15 kg} = \text{15 g/dose}[/latex]
  10. 37.7-56.55 mg/dose
    [latex]\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{83 lbs} = \text{37.7 kg}\\[/latex][latex]\dfrac{\text{1 mg}}{\text{1 kg}}\times\text{37.7 kg} = \text{37.7 mg/dose}\\[/latex][latex]\dfrac{\text{1.5 mg}}{\text{1 kg}}\times\text{37.7 kg} = \text{56.55 mg/dose}[/latex]

Practice Set 15.5: Verifying Dosage Safety

Practice Set 15.5: Verifying Dosage Safety – acetaminophen

All of the questions in this practice set use the following dosage information for acetaminophen. For each question, determine if the ordered dose is safe.

Drug guide dosage information:

1-3 months:
10 mg/kg/dose PO Q4H PRN (max 60 mg/kg/day)
20 mg/kg/dose PR Q6H PRN (max 80 mg/kg/day)

3 months of age to adolescents:
10 to 15 mg/kg/dose PO Q4H PRN (max 75 mg/kg/day)
20 mg/kg/dose PR Q6H PRN (max 80 mg/kg/day)

Usual adult dose:
325 to 650 mg/dose PO Q4 to 6H PRN (max 4 g/24 hr)

Questions:

  1. Client information:  12 year old weighing 41 kg
    Ordered dose: 
    500 mg PO Q4H prn
  2. Client information:  2 year old weighing 12 kg
    Ordered dose:
    250 mg PO Q4H prn
  3. Client information:  1 month old weighing 4 kg
    Ordered dose:
    80 mg PR Q6H prn
  4. Client information:  7 year old weighing 23 kg
    Ordered dose:
    300 mg PO Q4H prn
  5. Client information:  4 year old weighing 16 kg
    Ordered dose:
    125 mg PO Q4H prn
Answers:
  1. Yes, this is a safe dose. 500 mg is in the safe range of 410-615 mg.
    [latex]\text{min dose}=\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{41 kg}=\text{410 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{41 kg}=\text{615 mg}[/latex]
  2. No, this is not a safe dose. 250 mg is above the safe range of 120-180 mg.
    [latex]\text{min dose}=\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{12 kg}=\text{120 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{12 kg}=\text{180 mg}[/latex]
  3. Yes, this is a safe dose. 80 mg is the correct dose when given rectally (PR).
    [latex]\text{dose}=\dfrac{\text{20 mg}}{\text{1 kg}}\times\text{4 kg}=\text{80 mg}[/latex]
  4. Yes, this is a safe single dose. 300 mg is in the safe range of 230-345 mg.
    [latex]\text{min dose}=\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{23 kg}=\text{230 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{23 kg}=\text{345 mg}[/latex]
  5. No, this is not a safe dose. 125 mg is below the safe range of 160-240 mg.
    [latex]\text{min dose}=\dfrac{\text{10 mg}}{\text{1 kg}}\times\text{16 kg}=\text{160 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{15 mg}}{\text{1 kg}}\times\text{16 kg}=\text{240 mg}[/latex]

Practice Set 15.6: Verifying Dosage Safety

Practice Set 15.6: Verifying Dosage Safety – phenoxymethyl penicillin

All of the questions in this practice set use the following dosage information for phenoxymethyl penicillin (Penicillin V). For each question, determine if the ordered dose is safe.

Drug guide dosage information:

Children:
8-17 mg/kg/dose PO Q8H OR 6-13 mg/kg/dose PO Q6H (max: 3 g/day).

Adults:
300-600 mg/dose PO Q6-8H.

Prophylaxis for Asplenia:
>3 months to 5 years old: 150 mg PO BID.
>5 years old: 300 mg PO BID.

Questions:

  1. Client information:  6 year old weighing 22 kg
    Ordered dose: 
    300 mg PO Q8H
  2. Client information:  16 year old weighing 63 kg
    Ordered dose:  600 mg PO Q6H
  3. Client information:  8 year old weighing 25 kg
    Ordered dose:  600 mg PO Q8H
  4. Client information:  1 year old weighing 9 kg with asplenia
    Ordered dose:  300 mg PO BID
  5. Client information:  4 year old weighing 13 kg
    Ordered dose:  150 mg PO Q6H
Answers:
  1. Yes, this is a safe dose. 300 mg is in the safe range of 176-374 mg.
    [latex]\text{min dose}=\dfrac{\text{8 mg}}{\text{1 kg}}\times\text{22 kg}=\text{176 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{17 mg}}{\text{1 kg}}\times\text{22 kg}=\text{374 mg}[/latex]
  2. Yes, this is a safe dose. 600 mg is in the safe range of 378-819 mg.
    [latex]\text{min dose}=\dfrac{\text{6 mg}}{\text{1 kg}}\times\text{63 kg}=\text{378 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{13 mg}}{\text{1 kg}}\times\text{63 kg}=\text{819 mg}[/latex]
  3. No, this is not a safe dose. 600 mg is above the safe range of 200-425 mg.
    [latex]\text{min dose}=\dfrac{\text{8 mg}}{\text{1 kg}}\times\text{25 kg}=\text{200 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{17 mg}}{\text{1 kg}}\times\text{25 kg}=\text{425 mg}[/latex]
  4. No, this is not a safe dose. The dose for a 1 year old is 150 mg BID.
  5. Yes, this is a safe dose. 150 mg is in the safe range of 78-169 mg.
    [latex]\text{min dose}=\dfrac{\text{6 mg}}{\text{1 kg}}\times\text{13 kg}=\text{78 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{13 mg}}{\text{1 kg}}\times\text{13 kg}=\text{169 mg}[/latex]

Practice Set 15.7: Verifying Dosage Safety

Practice Set 15.7: Verifying Dosage Safety – metoclopramide

All of the questions in this practice set use the following dosage information for metoclopramide. For each question, determine if the ordered dose is safe.

Drug guide dosage information:

GI Hypomotility and GE Reflux:
Children: 0.1-0.2 mg/kg/dose PO/IV/IM up to QID (Maximum: 0.5 mg/kg/24 hr).
Adults: 10-15 mg/dose PO/IV/IM QID.

Chemotherapy Induced Nausea and Vomiting (N&V)*
1mg/kg/dose IV/PO prior to chemotherapy, then 0.04 mg/kg/dose IV/PO Q6H (Maximum: 10 mg/dose).
Alternate dosing: 1 mg/kg IV/PO Q6H*

Post-Op or Opioid-Induced Nausea and Vomiting:
Children: 0.1-0.2 mg/kg/dose IV Q6-8H PRN. (Maximum 0.5 mg/kg/24 hr)
Children > 14 years and Adults: 10 mg/dose IV Q6-8H PRN

Questions:

  1. Client information:  15 year old weighing 50 kg with GE reflux.
    Ordered dose: 
    5 mg PO QID prn
  2. Client information:  46 year old weighing 88 kg with GI hypomotility.
    Ordered dose:  15 mg PO QID
  3. Client information:  7 year old weighing 23 kg with post op N&V.
    Ordered dose: 
    2.5 mg IV Q8H prn
  4. Client information:  6 year old weighing 20 kg with chemo induced N&V.
    Ordered dose: 
    0.8 mg PO Q6H
  5. Client information:  12 year old weighing 41 kg with post op N&V.
    Ordered dose: 
    2.5 mg IV Q6-8H prn
Answers:
  1. Yes, this is a safe dose. 5 mg is in the safe range of 5-10 mg and does not exceed the daily maximum if all 4 prn doses were given.
    [latex]\text{min dose}=\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{50 kg}=\text{5 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{50 kg}=\text{10 mg}[/latex]
    Max daily total 25mg/day
  2. Yes, this is a safe dose for an adult with GI hypomotility as it is in the range of 10-15 mg/dose. This dose is not calculated by weight.
  3. Yes, this is a safe dose as 2.5 mg is in the safe range of 2.3-4.6 mg and does not exceed the daily maximum if all 3 prn doses were given.
    [latex]\text{min dose}=\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{23 kg}=\text{2.3 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{23 kg}=\text{4.6 mg}[/latex]
    Max daily total 11.6 mg/day.
  4. Yes, this is a safe dose and does not exceed the maximum single dose.
    [latex]\text{min dose}=\dfrac{\text{0.04 mg}}{\text{1 kg}}\times\text{20 kg}=\text{0.8 mg}[/latex]
  5. No, this is not a safe dose. 2.5 mg is below the safe range of 4.1-8.2 mg and therefore the drug will not be in therapeutic range and the child’s N&V would persist.
    [latex]\text{min dose}=\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{41 kg}=\text{4.1 mg}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{41 kg}=\text{8.2 mg}[/latex]

Practice Set 15.8: Verifying Dosage Safety

Practice Set 15.8: Verifying Dosage Safety – fentanyl

All of the questions in this practice set use the following dosage information for fentanyl. For each question, determine if the ordered dose is safe.

Drug guide dosage information:

Intermittent Dosing:
Infants: 1 to 2 mcg/kg/dose IV Q2-4H PRN (usual max 4 mcg/kg/dose)
Children: 1 to 2 mcg/kg/dose IV Q30-60 minutes PRN (usual adolescent starting dose: 25-50 mcg)
1 to 2 mcg/kg/dose buccal Q30-60 min. PRN. Maximum initial dose 50 mcg

Continuous IV infusion (by Acute Pain Service, ICU or Palliative Care Specialists only):
Usual dose: 1 -4 mcg/kg/hr. Higher doses may be required in palliative care or end of life symptom management with monitored titration.

Intubation Dosage:
2 to 5 mcg/kg/dose IV over 1-2 min.

Questions:

  1. Client information:  2 year old weighing 14 kg.
    Ordered dose: 
    20 mcg IV q30-60min prn (IV intermittent).
  2. Client information:  6 year old weighing 38 kg.
    Ordered dose:  190 mcg/hour IV (continuous infusion).
  3. Client information:  4 year old weighing 65 lbs.
    Ordered dose: 
    120 mcg IV over 1-2 min (intubation dose).
  4. Client information:  7 month old weighing 9 kgs.
    Ordered dose: 
    9 mcg IV Q2-4h prn (IV intermittent).
  5. Client information:  4 month old weighing 10 lbs.
    Ordered dose: 
    16 mcg IV Q2-4h prn (IV intermittent).
Answers:
  1. Yes, this is a safe dose. 20 mcg is in the safe range of 14-28 mcg.
    [latex]\text{min dose}=\dfrac{\text{1 mcg}}{\text{1 kg}}\times\text{14 kg}=\text{14 mcg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mcg}}{\text{1 kg}}\times\text{14 kg}=\text{28 mcg/dose}[/latex]
  2. No, this is a safe dose. 190 mcg is not in the safe range of 14.5-29 mcg.
    [latex]\text{min dose}=\dfrac{\text{1 mcg}}{\text{1 kg}}\times\text{38 kg}=\text{38 mcg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{4 mcg}}{\text{1 kg}}\times\text{38 kg}=\text{152 mcg/dose}[/latex]
  3. Yes, this is a safe dose. 120 mcg is in the safe range of 59-147.5 mcg.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{65 lbs}=\text{29.5 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{2 mcg}}{\text{1 kg}}\times\text{29.5 kg}=\text{59 mcg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{5 mcg}}{\text{1 kg}}\times\text{29.5 kg}=\text{147.5 mcg/dose}[/latex]
  4. Yes, this is a safe dose. 9 mcg is in the safe range of 9-18 mcg.
    [latex]\text{min dose}=\dfrac{\text{1 mcg}}{\text{1 kg}}\times\text{9 kg}=\text{9 mcg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mcg}}{\text{1 kg}}\times\text{9 kg}=\text{18 mcg/dose}[/latex]
  5. Yes, this is a safe dose. 16 mcg is in the safe range of 14.5-29 mcg and does not exceed the maximum initial dose for children.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{10 lbs}=\text{4.5 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{1 mcg}}{\text{1 kg}}\times\text{4.5 kg}=\text{4.5 mcg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mcg}}{\text{1 kg}}\times\text{4.5 kg}=\text{9 mcg/dose}[/latex]

Practice Set 15.9: Verifying Dosage Safety and Checking Orders

Practice Set 15.9: Verifying Dosage Safety and Checking Orders – furosemide

All of the questions in this practice set use the following dosage information for infants and children receiving furosemide. For each question, determine if the ordered dose is safe as well as checking the orders compared to the drug guide dosage information as you go.

Drug guide dosage information:

Oral Dose
Initial: 0.5-2 mg/kg/dose PO Q6H–Q24H
Maximum PO dose 4 mg/kg/dose

Parenteral Dose:
0.5-2 mg/kg/dose /IV Q6-24H PRN
Usual: 1 mg/kg/dose IV Q6-24H
Maximum single dose is 2 mg/kg/dose IV

Continuous IV Infusion in Critical Care areas:
0.1-0.5 mg/kg/hr

Questions:

  1. Client information:  3 year old weighing 43 lbs needing continuous IV infusion of furosemide in the PICU.
    Ordered dose: 
    9.75 mg/hour continuous IV infusion.
  2. Client information:  7 year old weighing 40 kgs, needing oral dosing of furosemide.
    Ordered dose:  20.4 mg/dose IV Q6h.
  3. Client information:  15 month old weighing 12 kgs, needing intermittent parenteral dosing of furosemide.
    Ordered dose: 
    18 mg/dose IV Q8h PRN.
  4. Client information:  4 year old weighing 38 lbs, needing oral dosing of furosemide.
    Ordered dose: 
    76 mg/dose PO Q6h.
  5. Client information:  3 month old weighing 9.7 lbs, needing continuous IV infusion of furosemide in the Emergency Department.
    Ordered dose: 
    2.2 mg/dose IV Q24h.
Answers:
  1. Yes, this is a safe dose. 9.75 mg/hr is in the safe range of 1.95-9.75 mg/hr with continuous infusion.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{43 lbs}=\text{19.5 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{19.5 kg}=\text{1.95 mg/hour}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{19.5 kg}=\text{9.75 mg/dose}[/latex]
  2. No, this is a safe dose but the route of what was ordered does not match what the patient needs. 20.4 mg is in the safe range of 20-80 mg/dose.
    [latex]\text{min dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{40 kg}=\text{20 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mg}}{\text{1 kg}}\times\text{40 kg}=\text{80 mg/dose}[/latex]
  3. Yes, this is a safe dose. 18 mg is in the safe range of 6-24 mg/dose.
    [latex]\text{min dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{12 kg}=\text{6 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mg}}{\text{1 kg}}\times\text{12 kg}=\text{24 mg/dose}[/latex]
  4. No, this is not a safe dose. 76 mg is not in the safe range of 8.65-34.6 mg/dose.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{38 lbs}=\text{17.3 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{17.3 kg}=\text{8.65 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{2 mg}}{\text{1 kg}}\times\text{17.3 kg}=\text{34.6 mg/dose}[/latex]
  5. No, 2.2 mg/dose would be correct dosing for continuous IV furosemide. The order is wrong because it is for intermittent IV dosing when the child needs continuous dosing of furosemide.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{9.7 lbs}=\text{4.4 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.1 mg}}{\text{1 kg}}\times\text{4.4 kg}=\text{0.44 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.5 mg}}{\text{1 kg}}\times\text{4.4 kg}=\text{2.2 mg/dose}[/latex]

Practice Set 15.10: Verifying Dosage Safety and Checking Orders

Practice Set 15.10: Verifying Dosage Safety and Checking Orders – methotrimeprazine

All of the questions in this practice set use the following dosage information for methotrimeprazine. For each question, determine if the ordered dose is safe as well as checking the orders compared to the drug guide dosage information as you go.

Drug guide dosage information:

Agitation, Aggression, Psychosis:
Children (<12 yrs):
Initial: 0.125 mg/kg/dose PO BID Increase gradually as needed to control agitation/psychosis.
IM: 0.06-0.125 mg/kg/dose IM once daily or div. TID.
Maximum: 40 mg/24 hr.

Adolescents/Adults:
Initial: 2.5-10 mg PO BID-TID Increase gradually as needed to control agitation/psychosis. In severe cases may start with 25 mg PO BID-TID, IM: 25 mg IM BID-QID

Pain, Agitation, Delirium (Palliative Care):
0.05-0.2 mg/kg/dose PO/IV Q6-8H PRN. When titrating IV doses, may give Q30-60 min until stable dose is reached.
Maximum 0.5 mg/kg/dose (50 mg/dose)

Questions:

  1. Client information:  10 year old weighing 74.5 lbs, needing intermittent IV administration of methotrimeprazine for delirium symptoms during palliation.
    Ordered dose: 
    3.7 mg/hour IV, after titration.
  2. Client information:  5 year old weighing 18 kgs, needing oral dosing of methotrimeprazine for agitation and aggression.
    Ordered dose:  1.1 mg/dose PO BID.
  3. Client information:  14 year old weighing 120 lbs, needing oral dosing of methotrimeprazine to control psychosis and agitation symptoms.
    Ordered dose: 
    96 mg/dose PO BID.
  4. Client information:  3 year old weighing 32 lbs, needing intramuscular dosing of methotrimeprazine for agitation.
    Ordered dose: 
    1.5 mg/dose IM once daily.
  5. Client information:  17 month old weighing 22 lbs, needing intermittent IV administration of methotrimeprazine for pain and delirium symptoms during palliation.
    Ordered dose: 
    1.5 mg/dose PO Q6h PRN.
Answers:
  1. No, this is a safe dose. 3.7 mg is in the safe range of 1.68-6.72 mg but the timing is off. The order is for continuous IV dosing when the patient needs intermittent IV administration.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{74 lbs}=\text{33.6 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.05 mg}}{\text{1 kg}}\times\text{33.6 kg}=\text{1.68 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{33.6 kg}=\text{6.72 mg/dose}[/latex]
  2. No, this would be a safe but ineffective dose, it is too low. There is no range, you would start at 2.25 mg/dose. The rest of the order is correct.
    [latex]\text{dose}=\dfrac{\text{0.125 mg}}{\text{1 kg}}\times\text{18 kg}=\text{2.25 mg/dose}[/latex]
  3. No, the weight does not matter, 2.5-10 mg PO BID-TID is the generic range.
  4. Yes, this is a safe dose. 1.5 mg is in the safe range of 0.87-1.81 mg/dose.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{32 lbs}=\text{14.5 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.06 mg}}{\text{1 kg}}\times\text{14.5 kg}=\text{0.87 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.125 mg}}{\text{1 kg}}\times\text{14.5 kg}=\text{1.81 mg/dose}[/latex]
  5. No, the patient needs intermittent IV not oral, like what was ordered. Though 1.5 mg is within the safe range of 0.5-2 mg/dose and Q6-8h PRN is corrent.
    [latex]\text{weight conversion}=\dfrac{\text{1 kg}}{\text{2.2 lbs}}\times\text{22 lbs}=\text{10 kg}\\[/latex][latex]\text{min dose}=\dfrac{\text{0.05 mg}}{\text{1 kg}}\times\text{10 kg}=\text{0.5 mg/dose}\\[/latex][latex]\text{max dose}=\dfrac{\text{0.2 mg}}{\text{1 kg}}\times\text{10 kg}=\text{2 mg/dose}[/latex]

 

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A Guide to Numeracy in Nursing by Julia Langham is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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