Transcript Rau_Chapter_004

Chapter 4
Calculating Drug Doses
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Systems of Measure

The metric system


The International System of Units


Meter, kilogram, second
Drops as units of volume


Meter, liter, gram
Standard: 16 drops (gtts) = 1 ml
Household units of measure

Teaspoon, tablespoon, cup
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Doses From
Prepared-Strength Liquids,
Tablets, and Capsules



Calculating with proportions
Drug amounts in units
Calculations with a dosage schedule
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating with Proportions


Convert to consistent units of measure
Set up a straightforward proportion:
Original Dose
Per Amount
=
Desired Dose
Per Amount
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Drug Amounts in Units
Original Dose
Amount
=
Desired Dose
Amount
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculations with a Dosage
Schedule

Calculate the dose needed


mg/kg
Calculate the amount of the preparation:
Original Dose
Per Amount
=
Desired Dose
Per Amount
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Doses From
Percentage-strength Solutions

Types of percentage preparations



Weight to weight
Weight to volume
Volume to volume
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Doses From
Percentage-strength Solutions

Solutions by ratio



Ratio by grams to milliliters
Ratio by simple parts
Solving percentage-strength solution
problems

Three equations
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Solving Percentage-strength
Solution Problems (Equation 1)
% Strength =
Solute
Total Amount
--Percent strength is in decimals
--Solute is in grams or cubic centimeters
--Total amount = (solute + solvent)
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Solving Percentage-strength
Solution Problems (Equation 2)
Amount of Solute =
Total Amount
Amount of Solute
100 Parts
--100 parts = grams or cubic centimeters
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Solving Percentage-strength
Solution Problems (Equation 3)
% Strength= (Dilute Solute)x(% Strength of Solute)
Total Amount
--Percentage strength is in decimals
--Total amount = solution
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Doses From
Percentage-strength Solutions

Diluents and drug doses

Amount of diluent affects only the amount of time
required to administer the drug; amount of active
drug is the same
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Intravenous Infusion
Rates


Total solution over time
Amount of drug per unit of time
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Intravenous Infusion
Rates

Total solution over time:
Flow Rate (ml/min) = Total Solution (ml)
Time (min)
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Intravenous Infusion
Rates

Amount of drug per unit of time (Equation 5):
Concentration (amount/ml) = Total Drug Amount
Total Solution (ml)
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Intravenous Infusion
Rates

Amount of drug per unit of time (Equation 6):
Flow Rate (ml/min) = Amount x Milliliter
Minute
Amount
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.
Calculating Intravenous Infusion
Rates

Amount of drug per unit of time (Equation 7):
Flow Rate (drops/min) = Amount × Milliliters × Drops
Minute
Amount Milliliter
Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc.