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This chapter explores different systems of measure for drug doses, including the metric system, household units, and drops. It also covers calculating doses from prepared-strength liquids, tablets, capsules, and percentage-strength solutions. Learn how to calculate doses using proportions and dosage schedules, and calculate intravenous infusion rates.
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Chapter 4 Calculating Drug Doses
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
Calculating Doses From Prepared-Strength Liquids, Tablets, and Capsules • Calculating with proportions • Drug amounts in units • Calculations with a dosage schedule
Calculating with Proportions • Convert to consistent units of measure • Set up a straightforward proportion: Original Dose = Desired Dose Per Amount Per Amount
Drug Amounts in Units Original Dose = Desired Dose Amount Amount
Calculations with a Dosage Schedule • Calculate the dose needed • mg/kg • Calculate the amount of the preparation: Original Dose = Desired Dose Per Amount Per Amount
Calculating Doses From Percentage-strength Solutions • Types of percentage preparations • Weight to weight • Weight to volume • Volume to volume
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
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)
Solving Percentage-strength Solution Problems (Equation 2) Amount of Solute = Amount of Solute Total Amount 100 Parts --100 parts = grams or cubic centimeters
Solving Percentage-strength Solution Problems (Equation 3) % Strength= (Dilute Solute)x(% Strength of Solute) Total Amount --Percentage strength is in decimals --Total amount = solution
Calculating DosesFrom 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
Calculating Intravenous Infusion Rates • Total solution over time • Amount of drug per unit of time
Calculating Intravenous Infusion Rates • Total solution over time: Flow Rate (ml/min) = Total Solution (ml) Time (min)
Calculating Intravenous Infusion Rates • Amount of drug per unit of time (Equation 5): Concentration (amount/ml) = Total Drug Amount Total Solution (ml)
Calculating Intravenous Infusion Rates • Amount of drug per unit of time (Equation 6): Flow Rate (ml/min) = Amount x Milliliter Minute Amount
Calculating Intravenous Infusion Rates • Amount of drug per unit of time (Equation 7): Flow Rate (drops/min) = Amount×Milliliters×Drops Minute Amount Milliliter