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Math and Dosage Calculations for Health

Care Third EditionBooth & Whaley

Chapter 8: Oral Dosages

McGraw-Hill

© 2010 The McGraw-Hill Companies, Inc. All rights reservedMcGraw-Hill

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8.1 Distinguish different types of oral medications.

8.2 Recognize the types of solid oral medications that may not be altered by crushing or opening them.

8.3 List appropriate techniques for administering medication to patients with difficulty swallowing or with feeding tubes.

Learning Outcomes

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Learning Outcomes

8.4 Accurately calculate the amount of solid or liquid oral medication to administer to a patient.

8.5 Identify common errors that occur in calculating and preparing dosages for oral administration or via a feeding tube.

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Introduction

You will learn to apply the simple calculation methods learned in Chapter 7 to oral dosages

Including solids and liquids

Follow the method of calculation that you have chosen by following the color coded examples

Remember that excellence is a must with dosage calculations.

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Tablets and Capsules

Solid oral medications come in several forms:TabletsCapletsCapsulesGelcaps

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Tablets and Capsules (cont.)

TabletsMost common form of solid oral medications

Combination of an amount of drug with inactive ingredients

Administration formsSublingualBuccalChewable

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Dissolvable For swallowing

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Tablets and Capsules (cont.)

CapletsOval-shaped

Special coating – easier to swallow

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Tylenol caplets

Tylenol caplets

Tylenol caplets

Tylenol caplets

Tylenol caplets

Tylenol caplets

500 mg

500 mg

500 mg500 mg

500 mg500 mg

Tylenol caplets

Tylenol caplets

500 mg500 mg

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Tablets and Capsules (cont.)

CapsulesOval-shaped gelatin shells

containing medication in powder or granule form

The shell is usually two pieces that fit together

Can be separated to remove the medication if patient cannot swallow a pill

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Tablets and Capsules (cont.)

GelcapsA liquid medication

in a gelatin shell

Not designed to be opened

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Tablets and Capsules (cont.)

Scored tabletsAllows the tablet to be divided

when smaller doses are orderedMost often, scored tablets divide

into halvesSome divide into thirds or quarters

Medication is evenly distributed throughout the tablet

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Tablets and Capsules – Calculating Dosages

Rule 8-1Rule 8-1

Always question and/or verify when your calculation indicates to give a portion of a tablet when the tablet is not scored.

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Never attempt to break a tablet that is not

scored.

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Tablets and Capsules – Calculating Dosages (cont.)

Rule 8-2 Rule 8-2 Question and recheck any calculation that

indicates that you should administer more than three tablets or capsules.

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Tablets and Capsules – Calculating Dosages (cont.)

Rule 8-3 Rule 8-3 Follow these steps when determining the amount of medication to administer to a patient:

1. If necessary, convert the dosage ordered (O) to the desired dose (D) that has the same unit of measurement as the dose on hand (H).

2. Calculate the amount to administer by the method of your choice.

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Tablets and Capsules – Calculating Dosages (cont.)

Rule 8-3Rule 8-3 (cont.)

4. Apply critical thinking skills to determine whether the amount you have calculated is reasonable using Rules 8-1 and 8-2.

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Recheck your calculation if necessary

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Practice

The order is to give the patient 15 mg mirtazapine PO now.

You have 30 mg scored tablets available.

Calculate the correct amount of medication to administer using one of the following methods.

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Fraction Proportion Method

Procedure 7-1: Calculating the Amount to Administer by Fraction Proportion:

1. Set up the proportion as follows: dosage unit amount to administer dose on hand desired dose

2. Cancel units.

3. Cross multiply, then solve for the unknown value.

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Ratio Proportion Method

Procedure 7-2: Calculating the Amount to Administer by Ratio Proportion:

1. The proportion will be set up as follows:dosage unit : dose on hand :: amount to administer :

desired dose or

Q : H :: A : D2. Cancel units.

3. Multiply the means and extremes then solve for the missing value.

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Dimensional Analysis Method

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis:

With dimensional analysis you will not need to calculate the desired dose and amount to administer separately.

You will place your unknown (amount to administer) on one side of the equation then multiply a series of factors on the right side of the equation.

Canceling units will help you determine the equation has been set up correctly.

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Dimensional Analysis Method (cont.)

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis (cont.):

1. Determine the units of measure for the answer and place it as the unknown on one side of the equation.

2. On the right side of the equation, write a conversion factor with the units of measurement for the desired dose on top and the unit of measurement for the dose on hand.

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Dimensional Analysis Method (cont.)

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis (cont.):

3. Multiply the conversion factor by a second factor: the dosage unit over the dose on hand.

4. Multiply by a third factor: dose ordered over the number one.

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Dimensional Analysis Method (cont.)

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis (cont.):

5. Cancel units on the right side of the equation. The remaining unit of measure on the right side of the equation should match the unknown unit of measure on the left side of the equation.

6. Solve the equation.

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Formula Method

Procedure 7-4 : Calculating Amount to Administer Using the Formula Method:

1. Determine the desired dose. Determine the dose on hand (H) and dosage unit (Q)

2. Fill the formula• D for the desired dose• H for the dose on hand • Q for the dosage unit in the formula • A for the unknown or the amount to administer

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AxQ HD

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Formula Method (cont.)

Procedure 7-4 : Calculating Amount to Administer Using the Formula Method:

3. Cancel the units.

4. Solve for the unknown.

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AxQ HD

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Crushing Tablets or Opening Capsules

Who benefits?Patients who have difficulty swallowing pillsPatients who have tube feedings

Check the policyMay need physician order first

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Crushing Tablets or Opening Capsules (cont.)

Mixing with food Prepare tablet or

capsule Mix with soft foods or

liquids

Check for interactions before mixing

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Some Common Food and Drug Interactions

DRUG FOOD INTERACTION

Antipsychotics Coffee and tea Reduces effectiveness of drug

Bronchodilators Caffeine Stimulation of the nervous system

CNS depressants Black cohosh, ginseng, kava kava, St. John’s wort, valerian, ETOH

Intensified sedative effects drug

Erythromycin Acidic fruits, juices; carbonated beverages

Decreased antimicrobial activity

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Some Common Food and Drug Interactions (cont.)

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DRUG FOOD INTERACTION

Ferrous sulfate

Tea Decreased absorption

Haloperidol Coffee and tea Decreased absorption

Insulin Coffee Stimulated excretion

MAO inhibitors Foods with tryamine (hard cheeses, chocolate, red wine, and beef or chicken liver)

Headache, nosebleed,

chest pain, severe hypertension

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DRUG FOOD INTERACTION

Tetracyclines Dairy products Reduced effectiveness of the drug

Antihystamines, cholesterol lowering agents, calcium channel blockers

Grapefruit and grapefruit juice

Muscle aches, fatigue, increase side effects

Some Common Food and Drug Interactions (cont.)

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Crushing Tablets or Opening Capsules (cont.)

Tube feedingsDissolve the crushed tablet

or opened capsule in a small amount of warm water.

If medication cannot be crushed, check for an alternative form and ask the physician to change the order.

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Crushing Tablets or Opening Capsules (cont.)

Enteric-coated tablets Coating dissolves only in an

alkaline environment such as the small intestine

Deliver medication that would be destroyed by the stomach acid or that could injure the stomach lining

Must never be crushed, broken, or chewed

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Crushing Tablets or Opening Capsules (cont.)

Sustained-Release MedicationsDrug is released slowly into

the bloodstream

If scored, break at scored line

Do not crush or dissolve – allows too much medication to be absorbed at one time

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Crushing Tablets or Opening Capsules (cont.)

Spansules Contain granules of medication with

different coatings that delay release of some of the medication

Spansules may be opened and the granules gently mixed with soft food

Do not crush or dissolve the granules

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Crushing Tablets or Opening Capsules (cont.)

Rule 8-4Rule 8-4 To prevent an incorrect dose of medication, do not crush or otherwise alter any of the following: Enteric-coated tablets

Sustained-release forms of medication

Any tablet with a hard shell or coating

Tablets for sublingual or buccal use

Capsules with seals that prevent separating the two parts

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Drugs that must notmust not be crushed / dissolved

Indication of sustained-release drugs:-Bid LA Tempule

-Dur CR Chronotab

Plateau Cap XL Repetab

Span Sequel Tembid

SA Spansule

SR Extentab

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Crushing Tablets or Opening Capsules (cont.)

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Crushing Tablets or Opening Capsules (cont.)

Drugs that must notmust not be crushed / dissolved

Indication of enteric-coated drugs:

EC

Enseal

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Liquid Medications

Greater range of dosages possible

Easier to swallowChildrenElderly

May be less stableReconstitutionRefrigeration

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Liquid Medications (cont.)

Rule 8-5 Rule 8-5 Reconstituting Liquid Medications:

Use only the liquid specified on the drug label.

Use the exact amount of liquid specified on the drug label.

Check the label to determine whether the medication should be shaken before administering.

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Liquid Medications (cont.)

Rule 8-5 Rule 8-5 (cont.)

Check the label to determine whether the reconstituted medication must be refrigerated.

Write on the label Date and time of reconstitution Your initialsStrength, if necessary

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Liquid Medications (cont.)

Rule 8-5 Rule 8-5 (cont.)

Check the label to determine how long the reconstituted medication may be stored.

Discard any medication left after this time period has passed.

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Rule 8-5 Rule 8-5 (cont.)

When medication can be reconstituted in different strengths, select the strength that will allow the desired dose in the smallest volume.

Read the order carefully when calculating the amount to administer.

Dose is usually ordered in units of drug, not volume of liquid.

Calculate the volume needed to administer the desired dose.

Liquid Medications (cont.)

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Liquid Medications (cont.)

To calculate the volume of liquid oral medication to administer use: Fraction proportion

Ratio proportions

Formula

Dimensional analysis

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QHD

A

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Practice

Find the amount to administer.

Ordered: Ventolin 5 mg PO now On hand: Ventolin syrup 2 mg per 5 mL

Use the calculation method of choice.

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Liquid Medications (cont.)

Procedure 7-1: Calculating the Amount to Administer by Fraction Proportion:

1. Set up the proportion as follows: dosage unit amount to administer dose on hand desired dose

2. Cancel units.

3. Cross multiply, then solve for the unknown value.

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=

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Liquid Medications (cont.)

Procedure 7-2: Calculating the Amount to Administer by Ratio Proportion:

1. The proportion will be set up as follows:dosage unit : dose on hand :: amount to administer :

desired dose or

Q : H :: A : D2. Cancel units.

3. Multiply the means and extremes then solve for the missing value.

8-44

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Liquid Medications (cont.)

Procedure 7-3: Calculating the Amount to Administer by Dimensional Analysis:

With dimensional analysis you will not need to calculate the desired dose and amount to administer separately.

You will place your unknown (amount to administer) on one side of the equation then multiply a series of factors on the right side of the equation.

Canceling units will help you determine the equation has been set up correctly.

8-45

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Liquid Medications (cont.)

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis (cont.)

1. Determine the units of measure for the answer and place it as the unknown on one side of the equation.

2. On the right side of the equation, write a conversion factor with the units of measurement for the desired dose on top and the unit of measurement for the dose on hand.

3. Multiply the conversion factor by a second factor: the dosage unit over the dose on hand.

8-46

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Liquid Medications (cont.)

Procedure 7-3 Calculating the Amount to Administer by Dimensional Analysis (cont.):

4. Multiply by a third factor: dose ordered over the number one.

5. Cancel units on the right side of the equation. The remaining unit of measure on the right side of the equation should match the unknown unit of measure on the left side of the equation.

6. Solve the equation.

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Liquid Medications (cont.)

Procedure 7-4: Calculating Amount to Administer Using the Formula Method:

1. Determine the desired dose. Determine the dose on hand (H) and dosage unit (Q)

2. Fill the formula D for the desired dose H for the dose on hand Q for the dosage unit in the formula A for the unknown or the amount to administer

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AxQHD

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Liquid Medications (cont.)

Procedure 7-4: Calculating Amount to Administer Using the Formula Method:

3. Cancel the units.

4. Solve for the unknown.

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AxQHD

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Patient Education

Read the label to learn how to store the medication.

Use the measuring device provided or a device specifically made for measuring medications.Household teaspoons and tablespoons do

not always measure liquids accurately.

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Patient Education (cont.)

Do not store medication longer than the label indicates. May lose potency Chemical composition may change

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Patient Education (cont.)

Wash measuring device after each use. Use hot water and dish detergentDry thoroughlyStore in clean container

Keep liquid medication in original container.

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True or False___ Any tablet can be broken in half to give a

patient the correct dose.

___ Enteric coated tablets can be crushed and given through an NG tube.

____ Some spansules can be pulled apart so the granules can be given with applesauce.

Apply Your Knowledge

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T

F

FOnly scored tablets should be broken.

Medication could be broken down by stomach acid or it could injure the stomach lining.

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Apply Your Knowledge

Which of the following foods are contraindicated to mix with tetracyclines?

A. Water

B. Orange juice

C. Milk

D. Applesauce

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Apply Your Knowledge

Which of the following types of medications may be crushed for administration?

A. Scored tablets

B. Enteric-coated tablets

C. Sustained-release tablets

D. Spansules

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Apply Your Knowledge

What preparation must be done before administering a crushed medication through a nasogastric tube?

A. Nothing special is needed

B. Mix the medication with applesauce

C. Mix the medication with warm water

D. Mix the medication with ice cream

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End of Chapter 8

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If you want to

achieve

excellence,

you can get

there today.

As of this

second,

quit doing

less-than-

excellent

work.

-- Thomas John

Watson, Jr.