Math and Dosage Calculations for Medical Careers PowerPoint ® to accompany Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Second Edition Booth Whaley

Chapter 9 Parenteral Dosages

Chapter 9 3 Learning Objectives Calculate the amount of a parenteral medication to administer. Select the appropriate syringe. Correctly reconstitute powdered medications. Measure insulin doses correctly. When you have completed Chapter 9, you will be able to:

Chapter 9 4 Learning Objectives (con’t) Accurately calculate doses of inhalant, rectal, and transdermal medications. Identify errors that occur when calculating and preparing parenteral doses.

Chapter 9 5 Introduction Parenteral medications are not taken by mouth. They need to bypass the digestive tract. Injections Inhalants Rectal Transdermal

Chapter 9 6 Parenteral Medications Types Intramuscular (IM) Subcutaneous (SC) Intradermal (ID) Intravenous (IV)

Chapter 9 7 Calculating Parenteral Dosages  Injections are mixtures that contain the drug dissolved in an appropriate liquid.  Dosage or medication strength on the label indicate the amount of drug contained within a volume of solution.  For example lidocaine 1% has 1 g lidocaine in 100 mL

Chapter 9 8 Calculating Parenteral Dosages (con’t)  Dosage strength may be in milligrams per milliliter as a percent or as a ratio.  Physician will order specific amount of the medication to be given.  You must calculate how many milliliters of solution contain the desired dose.

Chapter 9 9  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. Calculating Parenteral Dosages (con’t)

Chapter 9 10  After you determine the amount to give, you must select the appropriate syringe and needle. Calculating Parenteral Dosages (con’t)

Chapter 9 11  You must also select the correct needle length and gauge. Calculating Parenteral Dosages (con’t)

Chapter 9 12 Calculating Parenteral Dosages (con’t) Rule 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.

Chapter 9 13 Amount to be administered is calculated at 0.6 mL. Since this is less than 1 mL and greater than 0.5 mL, a tuberculin syringe should be used. Calculating Parenteral Dosages (con’t) Example

Chapter 9 14 Calculating Parenteral Dosages (con’t) Rule 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).

Chapter 9 15 Amount to be administered is calculated at 1.66 mL. - - Since the volume is greater than 1 mL you would round to the nearest tenth, which is 1.7 mL. Amount to be administered is calculated at mL. -- Since the volume is less than 1 mL you would round to the nearest hundredth, which is 0.53 mL. Calculating Parenteral Dosages (con’t) Example

Chapter 9 16 You must decide whether the amount to be administered can be safely injected in a single 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. Calculating Parenteral Dosages (con’t)

Chapter 9 17 Calculating Parenteral Dosages (con’t) 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 Rule Maximum volumes for infections: Intramuscular Injections

Chapter 9 18 Calculating Parenteral Dosages (con’t) Subcutaneous injections 1 mL Dosages larger than these maximum volumes should be checked and verified. Rule Maximum volumes for infections:

Chapter 9 19 Calculating Parenteral Dosages (con’t) Find the amount to administer and select the proper syringe. Ordered: Compazine 7.5 mg IM On hand: Compazine 5 mg/mL Answer: 1.5 mL Standard syringe in a single injection Example: (Use favorite calculate method)

Chapter 9 20 Medications Expressed in Percent or Ratio Format 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. Rule When a solution strength is expressed as a percent or ratio:

Chapter 9 21 Medications Expressed in Percent or Ratio Format (con’t) 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 Answer: 3 mL - Divide into two syringes of 1.5 mL each in two different sites Example: Example: (Use favorite calculate method)

Chapter 9 22 Review and Practice Find the amount to administer. Answer: 0.6 mL in a 1 mL tuberculin syringe Ordered: Dilaudid 6 mg IM now On Hand: Excellent!

Chapter 9 23 Review and Practice Find the amount to administer. Answer: 2.3 mL in a standard syringe Ordered: Zinacef 500 mg IM On Hand: Zinacef (cefuroxime for injection) 750 mg Dosage strength after reconstitution is 220 mg/mL Excellent!

Chapter 9 24 Reconstituting Powdered Medications Medication which loses potency quickly in solution may be supplied in powdered form They are reconstituted by dissolving them in an appropriate solvent (or diluent) Instructions are provided in: Drug label Package insert PDR

Chapter 9 25 Reconstituting Powdered Medications (con’t) Determine the solvent to be used to dilute medication Sterile water Saline Bacteriostatic solution Some meds are packaged with separate container of the appropriate solvent

Chapter 9 26 Reconstituting Powdered Medications (con’t) Many meds are mixed with lidocaine (a local anesthetic) to reduce the pain. Label or package insert indicates when lidocaine can be used. Since lidocaine is a medication, you must have a physician’s order to use it.

Chapter 9 27 Do not confuse it with a combination of lidocaine and epinephrine. Epinephrine causes vasoconstriction (tightening of the blood vessels which delays medication absorption). The package lists how much solvent to combine with the medication. Reconstituting Powdered Medications (con’t)

Chapter 9 28 Reconstituting Powdered Medications (con’t) 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. Rule To reconstitute a powdered medication:

Chapter 9 29 Reconstituting Powdered Medications (con’t) 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. Rule (con’t)

Chapter 9 30 Reconstituting Powdered Medications (con’t) 5. Make sure the powdered medication is completely dissolved and that the solution is free of visible particles before using it. Rule (con’t)

Chapter 9 31 Error Alert! Select the correct instructions for the strength and route ordered.

Chapter 9 32 Review and Practice How much diluent should you add to this vial? Answer: 1 mL Wow, Great!

Chapter 9 33 Review and Practice Answer: 0.75 mL Ordered: Synagis 75 mg IM Q8H On hand: Excellent! What is the amount to administer?

Chapter 9 34 Other Medication Routes  Intradermal injections  Metered dose inhalers (MDI)  Rectal  Transdermal

Chapter 9 35 Other Medication Routes (con’t)  Metered dose inhalers (MDI) These provide a measured dose of medication in each puff.  Nebulizers  These are supplied as liquids which are mixed with sterile saline solution.  Single doses premixed with saline are available.  Multiple-dose containers usually come with special droppers for calibration.

Chapter 9 36 Intradermal Injections  Injected under the first layer of the skin  Often used for diagnostic testing such as tuberculosis or allergies  Usually 0.1 mL or less  Always use a tuberculin syringe

Chapter 9 37 Rectal Medications  Usually given in suppository form  Suppositories cannot be accurately divided

Chapter 9 38 Transdermal Systems  Patches A patch is a special membrane which releases liquid medication at a constant rate Adhesive edges A patch’s dosage strength is usually expressed in mg or mcg per hour A patch cannot be divided  Ointments  Creams

Chapter 9 39 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.

Chapter 9 40 Apply Your Knowledge 0.8 mL IM What kind of syringe would you use to administer 0.8 mL IM? Answer: Tuberculin syringe Answer: Standard syringe 2.3 mL IM What kind of syringe would you use to administer 2.3 mL IM?

Chapter 9 41 Apply Your Knowledge maximum  What is the maximum amount of medication that can be administered IM in one site to an adult? Answer: 3 mL

Chapter 9 42 Apply Your Knowledge 20% solution  A 20% solution means that there is 20 g in how many mL? Answer: 100 mL

Chapter 9 43 Parenteral Medications THE END The best way to escape from a problem is to solve it. -- Alan Saporta