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# Clinical Calculations: Module 4: Oral Medications

## Calculating Doses for Oral Medications

### Module 4 - Calculating Doses of Oral Medications

What’s in this module?

In this module, you will learn how to read labels on the manufacturer’s medication labels.  You will learn to calculate the correct amount of tablets, capsules, caplets, and oral solutions and suspensions to give a client.  The route of administration for all the medications in this module is oral (by mouth).

Summary of problem types in this module

Problems will involve reading medication labels and healthcare provider’s orders.  You will calculate the correct amount to give a client of tablets, capsules, and oral solutions, syrups, elixirs, and suspensions.

Oral solutions, syrups, elixirs, and suspensions are given in liquid form.  Suspensions contain small particles of medication that cannot dissolve, so shaking the medication before administration is essential.  The other forms of liquid medication are mixed with different types of solutions to change the taste or consistency of the medication.

Assume all questions ask for the amount per dose unless instructed otherwise.

Equivalents to know

You should now know all your commonly used equivalents.

Rounding rules to know

You will continue to use the rounding rules for numbers >1 and <1.

Here are the new rounding rules you need to learn:

1. For tablets, if you have a problem that works out to exactly 0.5 tablet, do not round your answer. If the answer works out to less than 0.5 tablet, round down to the next whole number. If the answer works out to greater than 0.5 tablet, round up to the next whole number.
2. Capsules are different. You cannot give a part of a capsule. Therefore, capsules must be rounded to a whole number. Less than half a capsule rounds down to the next lowest whole number. A half capsule and greater rounds up to the next whole number.

Note: Rounding rules for capsules are used for any tablet or caplet that cannot be split.

The SF is the amount of medication the healthcare provider has ordered.  The dose is usually stated in mg, mcg, or g.  In rare cases the dose of medication will be stated in units.

Problem Type 1 – Reading Medication Labels

The medication label below illustrates the typical parts of a manufacturer’s medication label.  The nurse will often not see the medication label if the hospital pharmacy delivers medication in small packages containing a single tablet or capsule.  In the case of liquid medication, the nurse will often need to know how to read this label.

Note that this label has both a generic and a trade name for the medication.

If the medication is generic, it will have no trade name.  The generic name is always required.  The generic name may be in lower-case type, but sometimes may be printed in upper-case type.

A trade name is always marked with the symbol  for trademark.  This symbol may be small and difficult to read, but it always follows the trade name.  The trade name usually begins with a capital letter, but this feature depends on the manufacturer.

On this label the expiration date is listed as 3/15/16.  This container of medication has expired and would not be given to a client.

There are 100 tablets in the container and each tablet contains 333 mg of medication.  The tablets are delayed-release and enteric-coated to protect the client’s stomach and would never be split or broken.

Rounding rules for capsules are used for any tablet or caplet that cannot be split.

The label below is for an oral suspension, a liquid.  Note that the total amount in the container is 120 ml.  The dosage strength is 100 mg per 5 ml.  For a liquid, the dosage strength will always be stated for a specific volume, usually a quantity of ml.

This label also contains storage instructions and instructions to shake well before using to mix the contents.  This medication is generic and has no trade name.

Problems involving reading a medication label would ask you to identify different items of information from the label, such as the dosage strength or the generic name of the medication.

You will gain more experience in reading medication labels as you work through the rest of this module.  Some problems will be presented with a label that contains information that will be essential for you to solve the problem correctly.

Problem Type 2 – Oral Liquids

Problems about oral liquids will involve oral suspensions and other solutions.  Children are often the clients given oral medications.

Precise measurement of the dose is essential and the nurse may use a medication cup, a graduated spoon, or a syringe without a needle.

Rounding rules for numbers >1 and <1 apply to oral liquids.

Shutterstock.com   Retrieved 12/10/18

In the illustration above, a syringe without a needle and a medication cup are shown.  Teaspoon (tsp) and milliliter (ml) measurement scales are shown on both the syringe and the cup.  For greater precision, use the measurement in ml.

Shutterstock.com   Retrieved 12/10/18

The syringe without a needle is easiest to use with an infant.

Oempromo.com  Retrieved 12/11/18

A hollow-handle spoon may also be used.  The markings for measurement of the dose are on the side of the hollow handle.

Shutterstock.com   Retrieved 12/10/18

A toddler or older child can cooperate with taking the medication and may also be able to use a hollow-handle spoon or a medication cup.

Here’s an example of a calculation problem involving an oral liquid medication:

epharmacy.com.au/images/productimages/43191/original.jpg     Retrieved 1/5/19

The healthcare provider has ordered 480 mg daily (once a day) of paracetamol elixir for a client.  How many ml will you give per dose?

Note that the drug label states the dosage strength as 240 mg per 5 ml.  Look closely – the strength is stated in small print. The label also states that the generic name for Panamax is paracetamol.

Here’s the problem set up in the dimensional analysis format:

SF = 480 mg

AU = ml

Equivalents:

240 mg = 5 ml

Equation for the dose in ml:

Here’s another example:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

The healthcare provider has ordered pantoprazole sodium oral suspension 80 mg daily in apple juice.  How many packets of the medication will you mix into the cup of apple juice?

Note that each packet contains 40 mg of pantoprazole sodium for use as an oral suspension.  The quantity of apple juice used is not relevant in this problem.

Here’s the problem set up in the dimensional analysis format:

SF = 80 mg

AU = packets

Equivalents:

40 mg = 1 packet

Equation for the dose in packets:

Problem Type 3 – Scored Tablets

When giving tablets, first notice the presence of scoring on the tablet.  Scoring is an indented line to help you split the tablet.  Scoring indicates that a tablet may be split if necessary.

Whenever possible, try to give the dose of medication with whole tablets to reduce any error that might occur when splitting a tablet.

The rounding rule for tablets will apply to scored tablets:

1. For tablets, if you have a problem that works out to exactly 0.5 tablet, do not round your answer. If the answer works out to less than 0.5 tablet, round down to the next whole number. If the answer works out to greater than 0.5 tablet, round up to the next whole number.

Do not split a tablet into parts smaller than one half.

Here’s an example of a calculation problem involving a scored tablet:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

The healthcare provider has ordered levothyroxine 150 mcg daily for a client.  You have on hand levothyroxine 175 mcg tablets.  How many tablets will you give per dose?

Here’s the problem set up in the dimensional analysis format:

SF = 150 mcg

AU = tablets

Equivalents:

175 mcg = 1 tablet

Equation for the dose in tablets:

In this case give 1 tablet, following the rounding rule for tablets.

Here’s another example:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

A healthcare provider has ordered lorazepam 1.5 mg as needed for anxiety.  Your client has become anxious and you need to give a dose of lorazepam.  Hoe many tablets will you give?

You have on hand Ativan 1 mg tablets (generic name lorazepam).  You note that the tablets are scored.

Here’s the problem set up in the dimensional analysis format:

SF = 1.5 mg

AU = tablets

Equivalents:

1.5 mg = 1 tablet

Equation for the dose in tablets:

In this case give 1.5 tablets, following the rounding rule for tablets.  Split one tablet on the score line to give the half tablet.

https://www.medofficedirect.com/pub/media/catalog/product/cache/74c1057f7991b4edb2bc7bdaa94de933/i/0/i08649.jpg  Retrieved 1/5/19

Your nursing station should have a pill cutter (pill splitter) to ensure accurate splitting of your tablets.  A small blade in the top of the pill cutter will split the tablet.

Problem Type 4 –Tablets without Scoring

Tablets without scoring may be enteric coated, time release (extended release) or have a protective film over the tablet.  These tablets may not be split.

Sometimes this type of tablet is elongated and called a caplet.  Treat caplets as tablets without scoring.

Use the rounding rule for capsules for tablets that may not be split.

Capsules are different. You cannot give a part of a capsule. Therefore, capsules have to be rounded to a whole number. Less than half a capsule rounds down to the next lowest whole number. A half capsule and greater rounds up to the next whole number.

Here’s an example of a calculation problem involving a tablet that may not be split:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

The client has a new order for divalproex sodium 900 mg by mouth twice a day.  You have on hand Depakote ER 500 mg (divalproex sodium) tablets.  How many tablets do you give for each dose?

Here’s the problem set up in the dimensional analysis format:

SF = 900 mg

AU = tablets

Equivalents:

500 mg = 1 tablet

Equation for the dose in tablets:

According to your rounding rules, give 2 tablets per dose.

Be sure to look up the appropriate dose in your drug reference.  Don’t forget: you can always call the healthcare provider if you have questions about an order.

Here’s another example:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

Your client has an order for clopidogrel (Plavix) 85 mg daily by mouth.  How many tablets will you give the client?  This tablet may not be split.

Here’s the problem set up in the dimensional analysis format:

SF = 85 mg

AU = tablets

Equivalents:

75 mg = 1 tablet

Equation for the dose in tablets:

According to your rounding rules, give 1 tablet per dose.

Problem Type 5 – Capsules

Do not split these medications.

1. Capsules are different. You cannot give a part of a capsule. Therefore, capsules must be rounded to a whole number. Less than half a capsule rounds down to the next lowest whole number. A half capsule and greater rounds up to the next whole number.

Here’s an example of a calculation problem involving a capsule:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

Your client has an order for amoxicillin 875 mg by mouth every twelve hours.  How many capsules will you give per dose?  (Amoxicillin is the generic name in this case.)

Here’s the problem set up in the dimensional analysis format:

SF = 875 mg

AU = capsules

Equivalents:

500 mg = 1 capsule

Equation for the dose in capsules:

According to your rounding rules, give 2 capsules per dose.

Here’s another example:

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

Your client has an order for venlafaxine extended release capsules 85 mg daily by mouth.  You have on hand Effexor XR 37.5 mg capsules (venlafaxine).  How many capsules will you give the client per dose?

Here’s the problem set up in the dimensional analysis format:

SF = 85 mg

AU = capsules

Equivalents:

37.5 mg = 1 capsule

Equation for the dose in capsules:

According to your rounding rules, give 2 capsules per dose.

Be sure to look up the appropriate dose in your drug reference.  Don’t forget: you can always call the healthcare provider if you have questions about an order.

Your practice problems start in the next section.  Use the dimensional analysis format to set up your problems so the methodology will become a habit for you.

Always refer to the rounding rule appropriate for the problem you are working.  You will become very familiar with the rounding rules.

Before you start a problem, be certain that you understand the form of the medication you are administering: liquid, scored tablet, coated tablet, or capsule.

## Practice Problems

### Module 4 Practice Problems

Use the Amoxicillin label for the first seven problems

1. Is the medication ready to use when the package is received?
1. What is the medication strength when it is ready to use?
1. Is amoxicillin a generic or trade name?
1. Who is the manufacturer?
1. A healthcare provider has ordered 350 mg of amoxicillin oral suspension twice daily by mouth for your client.  How many ml will you give?
1. The order in question 5 has changed to 500 mg twice daily.  How many ml will you give?
1. The order in question 5 has changed to 250 mg twice daily.  How many ml will you give?

Use the Avil label for problems 8-15.

cdn7.bigcommerce.com/s-km6aq5/images/stencil/500x659/products/82/268/avil_syrup__31295.1453802147.jpg?c=2

Retrieved 1/2/19

1. What is the trade name of this medication?
1. What is the generic name?
1. How many ml total are in the package?
1. What is the dosage strength?
1. Who is the manufacturer?
1.  A healthcare provider has ordered 10 mg of pheniramine maleate by mouth three times a day for your client.  How many ml will you give?
1. The order has changed to 17 mg per dose.  How many ml will you give?
1. The order has changed to 7.5 mg per dose.  How many ml will you give?

Use the illustration of baclofen for problems 16-18.

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

1.  Your client has a prescription for baclofen 30 mg by mouth three times daily.  How many tablets will you give?
1.  Your client’s prescription changes to baclofen 15 mg by mouth four times daily.  How many tablets will you give?
1.  Your client’s prescription changes to baclofen 25 mg by mouth four times daily.  How many tablets will you give?

Use the illustration of hydrochlorothiazide for problems 19-21.

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

1. Your client has a prescription for hydrochlorothiazide 25 mg by mouth daily.  How many tablets will you give?
1. Your client’s prescription changes to hydrochlorothiazide 37.5 mg by mouth daily.  How many tablets will you give?
1. Your client’s prescription changes to hydrochlorothiazide 12.5 mg by mouth daily.  How many tablets will you give?

Use the illustration of Flagyl for problems 22-25.

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

1.  A healthcare provider has prescribed metronidazole (Flagyl) 500 mg by mouth every 12 hours for your client.  How many tablets will you give?
1. The healthcare provider changes the prescription to metronidazole (Flagyl) 375 mg by mouth every 12 hours for your client.  How many tablets will you give?
1. The healthcare provider changes the prescription to metronidazole (Flagyl) 550 mg by mouth every 12 hours for your client.  How many tablets will you give?
1. The healthcare provider changes the prescription to metronidazole (Flagyl) 250 mg by mouth every 8 hours for your client.  How many tablets will you give?

Use the Keflex label for problems 26-33.

1. What is the generic name for the medication with the label above?
1.  What is the trade name?
1. What form does the medication take (tablets, capsules, liquid)?
1. Are there special instructions for storing the medication?
1. What is the strength of the medication?
1. What is the typical adult dose listed on the label?
1. What is the maximum dose that can be given per day according to the label?
1. A healthcare provider has prescribed cephalexin 125 mg by mouth every 12 hours for your client.  How many capsules will you give?

Use the illustration of Cymbalta for problems 34-38.

https://www.webmd.com/drugs/2/index   Retrieved 1/5/19

1. A healthcare provider has prescribed duloxetine (Cymbalta)  25 mg by mouth twice daily for your client.  How many capsules will you give?
1. A healthcare provider has prescribed duloxetine (Cymbalta) 35 mg by mouth twice daily for your client.  How many capsules will you give?
1. A healthcare provider has prescribed duloxetine (Cymbalta) 60 mg by mouth daily for your client.  How many capsules will you give?
1. A healthcare provider has prescribed duloxetine (Cymbalta) 55 mg by mouth daily for your client.  How many capsules will you give?
1. A healthcare provider has prescribed duloxetine (Cymbalta)  600 mg by mouth daily for your client.  How many capsules will you give?

### Answers to the Module 4 Practice Problems

The Amoxicillin problems (1-7):

1. Is the medication ready to use when the package is received?

No – the medication is in powder form and must be mixed with water according to the instructions on the label.

1. What is the medication strength when it is ready to use?

200mg per 5ml

1. Is amoxicillin a generic or trade name?

There is no trade name on the label.  The generic name is amoxicillin.

1. Who is the manufacturer?

Sandoz

1. A healthcare provider has ordered 350 mg of amoxicillin oral suspension twice daily by mouth for your client. How many ml will you give?

SF = 350 mg

AU = ml

Equivalent:

200 mg = 5 ml

Equation:

1. The order in question 5 has changed to 500 mg twice daily. How many ml will you give?

SF = 500 mg

AU = ml

Equivalent:

200 mg = 5 ml

Equation:

1. The order in question 5 has changed to 250 mg twice daily. How many ml will you give?

SF = 250 mg

AU = ml

Equivalent:

200 mg = 5 ml

Equation:

The Avil problems (8-15):

1. What is the trade name of this medication?

Avil

1. What is the generic name?

pheniramine maleate

1. How many ml total are in the package?

100 ml

1. What is the dosage strength?

15 mg per 5 ml

1. Who is the manufacturer?

Aventis

1. A healthcare provider has ordered 10 mg of pherniramine maleate by mouth three times a day for your client. How many ml will you give?

SF = 10 mg

AU = ml

Equivalent:

15 mg = 5 ml

Equation:

1. The order has changed to 17 mg per dose. How many ml will you give?

SF = 17 mg

AU = ml

Equivalent:

15 mg = 5 ml

Equation:

1. The order has changed to 17 mg per dose. How many ml will you give?

SF = 7.5 mg

AU = ml

Equivalent:

15 mg = 5 ml

Equation:

The Baclofen problems (16-18):

1. Your client has a prescription for baclofen 30 mg by mouth three times daily. How many tablets will you give?

SF = 30 mg

AU = tablets

Equivalent:

20 mg = 1 tablet

Equation:

These tablets are scored and may be split in half.

1. Your client's prescription changes to baclofen 15 mg by mouth four time daily. How many tablets will you give?

SF = 15 mg

AU = tablets

Equivalent:

20 mg = 1 tablet

Equation:

Using critical thinking: Based on the rounding rule for tablets, the answer rounds to 1 tablet.  Over the course of the day, the client would receive a total of 80 mg instead of 60 mg. You need to call the healthcare provider to make sure it is okay to increase the dose by that much.

1. Your client's prescription changes to baclofen 25 mg by mouth four times daily. How many tablets will you give?

SF = 25 mg

AU = tablets

Equivalent:

20 mg = 1 tablet

Equation:

Using critical thinking: This time the answer rounds down to 1 tablet. That may not be enough medication for the client over the course of the day. You need to call the healthcare provider in case the dose needs to be increased.

The Hydrochlorothiazide problems (19-21):

1. Your client has a prescription for hydrochlorothiazide 25 mg by mouth daily. How many tablets will you give?

SF = 25 mg

AU = tablets

Equivalent:

50 mg = 1 tablet

Equation:

These tablets are scored and may be split in half. See the rounding rule for tablets.

1.  Your client's prescription changes to hydrochlorothiazide 37.5 mg by mouth daily. How many tablets will you give?

SF = 37.5 mg

AU = tablets

Equivalent:

50 mg = 1 tablet

Equation:

Using critical thinking: Following the rounding rule for tablets, you round to 1 tablet.  Call the pharmacy to see if they have 25 mg tablets.  You would give 1.5 tablets with a strength of 25 mg. That way you can give the exact dose ordered.

1. Your client's prescription changes to hydrochlorothiazide 12.5 mg by mouth daily. How many tablets will you give?

SF = 12.5 mg

AU = tablets

Equivalent:

50 mg = 1 tablet

Equation:

Do not split a tablet into parts smaller than one half.

Using critical thinking: You have an order to give a medication. The strength of medication that you have on hand would mean that you would not give any medication at all (0 tablets). Therefore, you need to call the pharmacy to see if they have 25 mg tablets.  You would give 0.5 tablets with a strength of 25 mg per tablet.

The Flagyl problems (22-25):

1. A healthcare provider has prescribed metronidazole (Flagyl) 500 mg by mouth every 12 hours for your client. How many tablets will you give?

SF = 500 mg

AU = tablets

Equivalent:

500 mg = 1 tablet

Equation:

1. The healthcare provider changes the prescription to metronidazole (Flagyl) 375 mg by mouth every 12 hours for our client. How many tablets will you give?

SF = 375 mg

AU = tablets

Equivalent:

500 mg = 1 tablet

Equation:

Using critical thinking: Rounding up to a whole tablet may be too much medication for the client. Call the pharmacy to see if they have a smaller dose of the medication. If not, you need to call the healthcare provider to determine if it is okay to give the increased amount.

1. The healthcare provider changes the prescription to metronidazole (Flagyl) 550 mg by mouth every 12 hours for your client. How many tablets will you give?

SF = 550 mg

AU = tablets

Equivalent:

500 mg = 1 tablet

Equation:

Using critical thinking: Rounding down to 1 tablet means that the client is getting less medication that was prescribed. You need to call the healthcare provider to check the dose.

1. The healthcare provider changes the prescription to metronidazole (Flagyl) 250 mg by mouth every 8 hours for your client. How many tablets will you give?

SF = 250 mg

AU = tablets

Equivalent:

500 mg = 1 tablet

Equation:

Using critical thinking: These tablets are enteric coated. They cannot be split. Therefore, they are to be treated like capsules. That means you would have to round up to 1 tablet every 8 hours. That is twice the amount of medication prescribed by the healthcare provider. Call the pharmacy to see if they have tablets with a smaller dose. If not, call the healthcare provider to check the dose.

The Keflex problems (26-33):

1. What is the generic name for the medication?

cephalexin

1. What is the trade name?

Keflex

1. What form does the medication take (tablets, capsules, liquid)?

Capsules (pulvules)

1. Are there special instructions for storing the medication?

Yes. Temperature limits are on the label. Store at controlled room temperature 59 to 86 degrees Fahrenheit (15 to 30 degrees Celsius)

1. What is the strength of the medication?

250 mg per capsule

1. What is the typical adult dose listed on the label?

One capsule (pulvule) every 6 hours

1. What is the maximum dose that can be given per day according to the label?

4 grams per day

1. A healthcare provider has prescribed cephalexin 125 mg by mouth every 12 hours for your client. How many capsules will you give?

SF = 125 mg

AU = capsule

Equivalent:

250 mg = 1 capsule

Equation:

Using critical thinking: Capsules cannot be split. Therefore, 0.5 capsules rounds to 1 capsule. That is twice the amount of medication prescribed by the healthcare provider. Call the pharmacy to see if they have capsules with a dose of 125 mg. If not, call the healthcare provider to check the dose.

The Cymbalta problems (34-38):

1. A healthcare provider has prescribed duloxetine (Cymbalta) 25 mg by mouth twice daily for your client. How many capsules will you give?

SF = 25 mg

AU = capsule

Equivalent:

30 mg = 1 capsule

Equation:

Using critical thinking: Rounding to a whole capsule means the client will get more than the prescribed amount of medication. You need to call the healthcare provider to check the dose.  Before doing so, you may want to check to see if a smaller strength capsule exists.

1. A healthcare provider has prescribed duloxetine (Cymbalta) 35 mg by mouth twice daily for your client. How many capsules will you give?

SF = 35 mg

AU = capsule

Equivalent:

30 mg = 1 capsule

Equation:

Using critical thinking: Rounding down to one capsule means the client will receive less than the prescribed amount of medication. You need to call the healthcare provider to check the dose.

1. A healthcare provider has prescribed duloxetine (Cymbalta) 60 mg by mouth daily for your client. How many capsules will you give?

SF = 60 mg

AU = capsule

Equivalent:

30 mg = 1 capsule

Equation:

1. A healthcare provider has prescribed duloxetine (Cymbalta) 55 mg by mouth daily for your client. How many capsules will you give?

SF = 55 mg

AU = capsule

Equivalent:

30 mg = 1 capsule

Equation:

Using critical thinking: Rounding to 2 capsules means that the client would receive more than the prescribed amount of medication. You need to call the healthcare provider to check the dose.

1. A healthcare provider has prescribed duloxetine (Cymbalta) 600 mg by mouth daily for your client. How many capsules will you give?

SF = 600 mg

AU = capsule

Equivalent:

30 mg = 1 capsule

Equation:

Using critical thinking:  Do not give this medication!  The large number of capsules is not reasonable.  The dose is ten times the normal range for this medication.  Call the healthcare provider at once to check the dose.