1. Chapter 9: Parenteral Dosages
Math and Dosage Calculations for Health Care Third Edition Booth & Whaley
Chapter 9: Parenteral Dosages
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2. Learning Outcomes
9.1 Calculate the amount of a parenteral medication to administer.
9.2 Select the appropriate syringe.
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3. Learning Outcomes (cont.)
9.3 Correctly reconstitute powdered medications.
9.4 Calculate the amount of reconstituted medications to administer.
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4. Learning Outcomes (cont.)
9.5 Accurately calculate doses of inhalant, rectal, and transdermal medications.
9.5 Identify errors that occur when calculating and preparing parenteral doses.
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5. 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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6. 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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7. 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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8. 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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9. Calculating Parenteral Dosages (cont.)
After you determine the amount to give, you must select the appropriate syringe and needle.
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10. Calculating Parenteral Dosages (cont.)
You must also select the correct needle length and gauge.
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11. Calculating Parenteral Dosages (cont.)
Rule 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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12. 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.
Example
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13. Calculating Parenteral Dosages (cont.)
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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14. 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 mL The volume is less than 1 mL – round to the nearest hundredth – 0.53 mL
Examples
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15. 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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16. Calculating Parenteral Dosages (cont.)
Rule 9-3 Maximum volumes for injections:
Intramuscular Injections
Adult 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
Dosages larger than these maximum volumes are rare and should be checked and verified.
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17. Calculating Parenteral Dosages (cont.)
Ordered: Compazine 7.5 mg IM On hand: Compazine 5 mg/mL Find the amount to administer and select the proper syringe.
Example
Answer mL using a standard 3 mL syringe in a single injection
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18. Medications Expressed in Percent or Ratio Format
Rule 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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19. Medications Expressed in Percent or Ratio Format (cont.)
Find the amount to administer and select the proper syringe. Ordered: magnesium sulfate 300 mg IM On hand: magnesium sulfate 10% solution Patient: 75 pound 8-year-old female
Example
Answer 3 mL
Divide into two syringes of 1.5 mL each and inject at two different sites.
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20. Practice Find the amount to administer and select appropriate syringe.
Ordered: Valium 3 mg IM now
On Hand:
Answer mL Use a 1 mL tuberculin syringe
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21. 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
Answer mL in a standard syringe
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22. 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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23. 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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24. 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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25. Reconstituting Powdered Medications (cont.)
Rule 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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26. Reconstituting Powdered Medications (cont.)
Rule 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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27. Reconstituting Powdered Medications (cont.)
Rule 9-5 (cont.)
5. Make sure the powdered medication is completely dissolved
The solution must be free of visible particles
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28. 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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29. Reconstituting Powdered Medications (cont.)
Rule 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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30. Reconstituting Powdered Medications (cont.)
Rule 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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31. Error Alert!
Select the correct instructions for the strength and route ordered.
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32. Practice How much diluent should you add to this vial? Answer 1 mL
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33. Practice
Ordered: Synagis 75 mg IM Q8H On hand: What is the amount to administer?
Answer mL
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34. 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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35. 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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36. Other Medication Routes (cont.)
Rectal Medications
Usually given in suppository form
Suppositories cannot be accurately divided
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37. 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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38. Apply Your Knowledge
How would you interpret a label that reads as follows?
Heparin 5000 units/mL
Answer Each 1 mL contains units of heparin.
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39. 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?
Answer Tuberculin syringe
Answer Standard syringe
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40. Apply Your Knowledge
What is the maximum amount of medication that can be administered IM in one site to an adult?
Answer mL
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41. Apply Your Knowledge Answer 100 mL
A 20% solution means that there is 20 g in how many mL?
Answer mL
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42. End of Chapter 9 The best way to escape from a problem is to solve it.
-- Alan Saporta
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