Chapter 9: Parenteral Dosages Math and Dosage Calculations for Health Care Third Edition Booth & Whaley Chapter 9: Parenteral Dosages McGraw-Hill

Learning Outcomes 9.1 Calculate the amount of a parenteral medication to administer. 9.2 Select the appropriate syringe. McGraw-Hill

Learning Outcomes (cont.) 9.3 Correctly reconstitute powdered medications. 9.4 Calculate the amount of reconstituted medications to administer. McGraw-Hill

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. McGraw-Hill

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 McGraw-Hill

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 McGraw-Hill

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 McGraw-Hill

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. McGraw-Hill

Calculating Parenteral Dosages (cont.) After you determine the amount to give, you must select the appropriate syringe and needle. McGraw-Hill

Calculating Parenteral Dosages (cont.) You must also select the correct needle length and gauge. McGraw-Hill

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. McGraw-Hill

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 McGraw-Hill

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). McGraw-Hill

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 mL The volume is less than 1 mL – round to the nearest hundredth – 0.53 mL Examples McGraw-Hill

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. McGraw-Hill

Calculating Parenteral Dosages (cont.) 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 Dosages larger than these maximum volumes are rare and should be checked and verified. McGraw-Hill

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 1.5 mL using a standard 3 mL syringe in a single injection McGraw-Hill

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. McGraw-Hill

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. McGraw-Hill

Practice Find the amount to administer and select appropriate syringe. Ordered: Valium 3 mg IM now On Hand: Answer 0.6 mL Use a 1 mL tuberculin syringe McGraw-Hill

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 2.3 mL in a standard syringe McGraw-Hill

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 McGraw-Hill

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. McGraw-Hill

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 McGraw-Hill

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. McGraw-Hill

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. McGraw-Hill

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 McGraw-Hill

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 McGraw-Hill

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. McGraw-Hill

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. McGraw-Hill

Error Alert! Select the correct instructions for the strength and route ordered. McGraw-Hill

Practice How much diluent should you add to this vial? Answer 1 mL McGraw-Hill

Practice Ordered: Synagis 75 mg IM Q8H On hand: What is the amount to administer? Answer 0.75 mL McGraw-Hill

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 McGraw-Hill

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 McGraw-Hill

Other Medication Routes (cont.) Rectal Medications Usually given in suppository form Suppositories cannot be accurately divided McGraw-Hill

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 McGraw-Hill

Apply Your Knowledge How would you interpret a label that reads as follows? Heparin 5000 units/mL Answer Each 1 mL contains 5000 units of heparin. McGraw-Hill

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 McGraw-Hill

Apply Your Knowledge What is the maximum amount of medication that can be administered IM in one site to an adult? Answer 3 mL McGraw-Hill

Apply Your Knowledge Answer 100 mL A 20% solution means that there is 20 g in how many mL? Answer 100 mL McGraw-Hill

End of Chapter 9 The best way to escape from a problem is to solve it. -- Alan Saporta McGraw-Hill