© 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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© 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
© 2010 The McGraw-Hill Companies, Inc. All rights reservedMcGraw-Hill
9-2
9.1 Calculate the amount of a parenteral medication to administer.
9.2 Select the appropriate syringe.
Learning Outcomes
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9-3
9.3 Correctly reconstitute powdered medications.
9.4 Calculate the amount of reconstituted medications to administer.
Learning Outcomes (cont.)
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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.)
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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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Calculating Parenteral Dosages (cont.)
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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Calculating Parenteral Dosages (cont.)
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
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Calculating Parenteral Dosages (cont.)
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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Calculating Parenteral Dosages (cont.)
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
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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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Calculating Parenteral Dosages (cont.)
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.
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Calculating Parenteral Dosages (cont.)
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
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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
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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:
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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
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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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Reconstituting Powdered Medications (cont.)
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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Reconstituting Powdered Medications (cont.)
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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Reconstituting Powdered Medications (cont.)
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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Reconstituting Powdered Medications (cont.)
Rule 9-5Rule 9-5 (cont.)
5. Make sure the powdered medication is completely dissolved
The solution must be free of visible particles
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Reconstituting Powdered Medications (cont.)
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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Reconstituting Powdered Medications (cont.)
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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Reconstituting Powdered Medications (cont.)
Rule 9-6Rule 9-6 (cont.)
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
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Practice
Ordered: Synagis 75 mg IM Q8HOn hand:
What is the amount to administer?
9-33
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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Other Medication Routes (cont.)
Rectal Medications Usually given in suppository form
Suppositories cannot be accurately divided
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Other Medication Routes (cont.)
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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Apply Your Knowledge
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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Apply Your Knowledge
What is the maximum amount of medication that can be administered IM in one site to an adult?
9-40
Answer 3 mL
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Apply Your Knowledge
A 20% solution means that there is 20 g in how many mL?
9-41
Answer 100 mL
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End of Chapter 9
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The best way
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from a problem is to
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