Transcript class 5 chapter 9

Chapter 9
Calculating Drug Dosages
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
1
Learning Objectives
 Use formulas to determine the
dosages of tablets, capsules, or
liquids
 Use formulas to determine the total
number of tablets or capsules or the
amount of liquid to be ordered for a
specified time
 Use information about the
apothecaries', metric, and household
measurements systems to
accurately calculate drug dosages
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
2
Learning Objectives (cont.)
 Calculate dosages for parenteral
injections, including those for special
preparations such as insulin
 Calculate flow rates for infusions
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
3
Calculating Medication Dosages
Three Steps
1. Verify that the drug available is the
same
measurement system as the drug
dosage desired (convert if needed)
2. Reduce to lowest terms
3. Calculate the dosage quantity to be
administered
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
4
Drug Calculation Methods
 Fraction Method
 600 mg = 200 mg
x tablets
1 tablet
Solve for x
 Ratios or Proportion Method
 600 mg : x tablets :: 200 mg : 1 tablet
 Solve for x
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
5
Drug Calculation Methods
(cont.)
 Desired over Available Method
Desired units (conversion factor) ×
Quantity of drug form = Quantity to give
Quantity available (× conversion factor)
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
6
Forms of Oral Medications
 Capsules
 Cannot be broken or divided
 If amount to be given is more than 0.5,
round to next whole number
 Tablets
 Only divide if scored
 Coated tablets are not to be broken
 Liquids
 May be measured in a medication cup,
syringe, or calibrated dropper
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
7
Scored and Unscored Tablets
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
8
Parenteral Medications
 Medication available in three forms:
 Prefilled syringe labeled with specific
dosage
 For example: meperidine (Demerol) 100
mg in 1 mL
 Single-dose ampule or multiple-dose vial
labeled with a specific dosage per
volume
 For example: epinephrine (Adrenalin)
1:1000 in 0.1 mL
 A vial with powder that requires a
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
9
Insulin
 A critical medication that replaces the
insulin not being produced by the
patient’s pancreas
 Insulin comes in a standardized
measure called a “Unit”
 Smallest amounts may be given;
errors are critical
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
10
Insulin (cont.)
 Strengths
 U-100 (100 Units of insulin per 1 mL)
 U-500 (500 Units of insulin per 1 mL)
 Preparation 5 times stronger, rarely used
 Syringe
 Calibrated in Units also
 Tuberculin syringe used in emergency
 Minims used; 16 minims = 1 mL
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
11
U-100 Syringe
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
12
Tuberculin Syringe
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
13
Flow Rate Formula
 Gtts/min =
Volume to be administered × gtt
factor
Time in minutes
 Drop factor of tubing:
Macrodrip = 10, 15, or 20 gtt/mL
Microdrip = 60 gtt/mL
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
14
Question 1
The patient is prescribed prednisone
60 mg PO once daily. The pharmacist
sends 20 mg tablets to the nursing
unit. How many tablets should the
LPN give?
1. 1 tablet
2. 2 tablets
3. 3 tablets
4. 4 tablets
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
15
Question 2
Ancef 750 mg is ordered. The vial is
labeled 500 mg/1mL. How many mL
are needed?
1. 0.5 mL
2. 1 mL
3. 1.5 mL
4. 2 mL
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
16
Question 3
When mixing regular and NPH
insulin:
1. Draw up the NPH insulin first.
2. Draw up the regular insulin first.
3. Inject air into the regular insulin
first.
4. These two insulins should not be
mixed.
Copyright © 2013, 2010, 2006, 2003, 2000, 1995, 1991 by Mosby, an imprint of
Elsevier Inc.
17
Practice
 Pharmacy sends you Tagamet
(cimetidine) 1 g IV liquid / 1 mL.
 The order requests 300 mg IV be
given.
 How do you calculate this does?
 How much Tagamet do you draw up?
Practice
 Pharmacy sends esomeprazole 20mg
extended release capsule.
 Ordered: Nexium (esomeprazole) 20
mg/capsule
 How do you calculate this does?
 How much Nexium do you give?
Practice
 Ordered: Ampicillin 750 mg IVPB
every 6 hours.
 Pharmacy sent Ampicillin 1 g/ 5mL.
 How do you calculate this does?
 How much Ampicillin do you give?
Practice
 IV 0.9% solution to infuse 1000 mL
over 8 hr.
 How much infuses over 1 hour?
 If your gtt factor is 12 gtts/mL, how
many gtts/ mins will infuse the
solution at the correct rate?
Practice
 Insulin ordered: 25 units NPH and 12
units regular subcutaneous every AM.
 What supplies do you need?
 What is the total amount in the
syringe?
WARNING!!!!!
 Your calculation labels must be
correct or the answer is wrong!
 Your zero’s placement must be
correct in nursing terms or it’s wrong!
 Accuracy is the issue.
 Safety is the result.