Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 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  Meter, liter, gram  The International System of Units  Meter, kilogram, second  Drops as units of volume  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=Desired Dose Per AmountPer Amount

Mosby items and derived items © 2008, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. Drug Amounts in Units Original Dose=Desired Dose Amount Amount Amount 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=Desired Dose Per AmountPer 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 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 = Amount of Solute Total Amount 100 Parts Total Amount 100 Parts 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 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) 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) 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 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 Minute Amount Milliliter