© 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 9-1 Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter.

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

9-1

Math and Dosage Calculations for Health Care Third Edition

Booth & Whaley

Chapter 9: Parenteral Dosages


9-2

9.1 Calculate the amount of a parenteral medication to administer.

9.2 Select the appropriate syringe.

Learning Outcomes


9-3

9.3 Correctly reconstitute powdered medications.

9.4 Calculate the amount of reconstituted medications to administer.

Learning Outcomes (cont.)


9-4

9.5 Accurately calculate doses of inhalant, rectal, and transdermal medications.

9.5 Identify errors that occur when calculating and preparing parenteral doses.

Learning Outcomes (cont.)

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

Introduction Parenteral medications

Not taken by mouth

Bypass the digestive tract

Include Injections Inhalants Rectal Transdermal

Injection types Intramuscular – IM Subcutaneous –

Sub-Q Intradermal – ID Intravenous – IV

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Calculating Parenteral Dosages Injections

Mixtures that contain the drug dissolved in an appropriate liquid

Dosage or solution strength on the label The amount of drug contained within a

volume of solution

For example, lidocaine 1% has 1 g lidocaine in 100 mL

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Calculating Parenteral Dosages (cont.) Dosage strength expressed

In milligrams per milliliter As a percent As a ratio

Physician’s order specifies the amount of the medication

You must calculate how many milliliters of solution contain the desired dose

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Calculating Parenteral Dosages (cont.) You will calculate the amount to

administer starting with the dosage ordered, dose on hand, and dosage unit.

You may have to convert the units of the dosage ordered to the units of the desired dose.

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Calculating Parenteral Dosages (cont.) After you determine the amount to

give, you must select the appropriate syringe and needle.

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You must also select the correct needle length and gauge.

Calculating Parenteral Dosages (cont.)

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RRuleule 9-1 9-1 Selecting a syringe:

1. If the amount of injection to administer is 1 mL or more, use a standard 3 mL syringe.

2. If the amount of injection to administer is less than 1 mL, use a 1-mL tuberculin syringe.

3. If the amount of injection to administer is less than 0.5 mL, use a 0.5-mL tuberculin syringe.

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Amount to be administered

is calculated at 0.6 mL. Which syringe would you use?

Since this is less than 1 mL and greater than 0.5 mL, a tuberculin syringe should be used.

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Example Example



Rule 9-2 Rule 9-2 Rounding the Amount to Administer:

1. Round volumes greater than 1 mL to the nearest tenth (one decimal).

2. Round volumes less than 1 mL to the nearest hundredths (two decimals).

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Amount to be administered is calculated at 1.66 mL

The volume is greater than 1 mL – round to the nearest tenth – 1.7 mL

Amount to be administered is calculated at 0.532 mLThe volume is less than 1 mL – round to the nearest hundredth – 0.53 mL

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Examples Examples


Calculating Parenteral Dosages (cont.) Can the amount to be administered

be safely injected into one site?

If amount to administer exceeds the amount that can be safely given in one site, divide the amount into equal (or nearly equal) parts.

Administer them in separate sites.

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Rule 9-3 Rule 9-3 Maximum volumes for injections:

Intramuscular Injections Adult 3 mL Adult Deltoid (arm) 2 mL Child (6-12 years old) 2 mL Child (0-5 years old) 1 mL Infant (premature) 0.5 mL

Subcutaneous injections 1 mL

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Dosages larger than these maximum volumes are rare and should be checked and verified.



Ordered: Compazine 7.5 mg IM

On hand: Compazine 5 mg/mLFind the amount to administer

and select the proper syringe.

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Answer 1.5 mL using a standard 3 mL syringe in a single injection

Example Example


Medications Expressed in Percent or Ratio Format

Rule 9-4Rule 9-4 When a solution strength is expressed as a percent or ratio

1. Convert the percent or ratio to a dosage strength of g/mL, mg/mL, or units/mL.

2. Calculate the amount to administer; then apply Rules 9-1 to 9-3.

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Medications Expressed in Percent or Ratio Format (cont.)

Find the amount to administer

and select the proper syringe.

Ordered: magnesium sulfate 300 mg IMOn hand: magnesium sulfate 10% solutionPatient: 75 pound 8-year-old female

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Answer 3 mL Divide into two syringes of 1.5 mL each and inject at two different sites.

Example Example


Practice

Find the amount to administer and select appropriate syringe.

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Answer 0.6 mL Use a 1 mL tuberculin syringe

Ordered: Valium 3 mg IM now

On Hand:


Practice

Find the amount to administer.

Ordered: Zinacef 500 mg IM

On Hand: Zinacef (cefuroxime for injection) 750 mg

Dosage strength after reconstitution is 220 mg/mL

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Answer 2.3 mL in a standard syringe


Reconstituting Powdered Medications Medications that loose potency

quickly in solution Supplied in powdered form

Reconstituted using an appropriate diluent

Instructions are provided in: Drug label Package insert PDR

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Reconstituting Powdered Medications (cont.)

Determine the solvent to be used to dilute medication. Sterile water Saline Bacteriostatic solution

Some meds are packaged the appropriate solvent.

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Some meds are mixed with lidocaine (a local anesthetic). Decreases pain on injection

Label or package insert indicates when lidocaine can be used Do not confuse it with a combination of

lidocaine and epinephrine

Must have a physician’s order

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Rule 9-5Rule 9-5 To reconstitute a powdered medication:

1. Find the directions on the medication label or package insert.

2. Use a sterile syringe and aseptic (germ-free) technique to draw up the correct amount of the appropriate diluent.

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Rule 9-5Rule 9-5 (cont.)

3. Inject the diluent into the medication vial.

4. Agitate the mixture by rolling, inverting, or shaking the vial. Check the directions on the label or package insert for which of these methods to use.

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5. Make sure the powdered medication is completely dissolved

The solution must be free of visible particles

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Use the specified amount of diluent Too much – dosage strength is not correct Too little

Powder may not dissolve completely Dosage strength not correct

Single dose vials – reconstitute just before using

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Rule 9-6Rule 9-6 When you store a medication after reconstituting it:

1. Record the date, the time of expiration, and your name or initials.

2. For multiple-dose medications, also record the solution strength.

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3. Check the drug label or package insert for the length of time a reconstituted medication may be stored.

4. Storage time may depend on whether the medication is refrigerated.

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Error Alert!

Select the correct instructions for the strength and route ordered.

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PracticeHow much diluent should you

add to this vial?

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Answer 1 mL


Practice

Ordered: Synagis 75 mg IM Q8HOn hand:

What is the amount to administer?

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Answer 0.75 mL

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Other Medication Routes

Intradermal (ID) injections Small doses under first layer of skin

0.1mL or less with TB syringe

Screening for TB or allergies

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Other Medication Routes (cont.)

Inhalants Metered dose inhalers (MDI)

These provide a measured dose of medication in each puff.

No calculation needed

Nebulizers Liquids mixed with sterile saline solution

Single doses premixed with saline available Multiple-dose containers – special droppers

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Rectal Medications Usually given in suppository form

Suppositories cannot be accurately divided

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Transdermal Systems Patches

Releases liquid medication at a constant rate Adhesive edges Dosage strength expressed in mg or mcg per hour Cannot be divided

Ointments

Creams

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Apply Your Knowledge

How would you interpret a label that reads as follows?

Heparin 5000 units/mL

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Answer Each 1 mL contains 5000 units of heparin.

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What kind of syringe would you use to administer 0.8 mL IM?

What kind of syringe would you use to administer 2.3 mL IM?

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Answer Tuberculin syringe

Answer Standard syringe

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What is the maximum amount of medication that can be administered IM in one site to an adult?

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Answer 3 mL

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A 20% solution means that there is 20 g in how many mL?

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Answer 100 mL

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End of Chapter 9

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The best way

to escape

from a problem is to

solve it.

-- Alan

Saporta

© 2010 The McGraw-Hill Companies, Inc. All rights reserved McGraw-Hill 9-1 Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter.

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