Transcript Roach: Introductory Clinical Pharmacology

Introduction to Clinical
Pharmacology
Chapter 03Calculation of Drug Dosages and
Mathematical Review
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Multiple Check System
• Order entry, barcoding, and technologic
checks
• Best method: manual redundancy system
and the “5 rights and 3 checks” method.
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Drug Label Information
• Need drug, form, and dosage strength on
the drug label.
• Review the MAR
• Trade name = brand name; generic name =
official drug name
• Unit of Dose Method
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Use of Zero
• Always use a zero before decimal points in
drug dosages so the dosage is not incorrectly
read.
• .25 mg could be misread as 25 mg, rather
than 0.25 mg
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Review of Arithmetic: Fractions
• Fractions: Consists of a numerator and
denominator
– Proper fraction
– Improper fraction
– Mixed numbers and improper fractions
• Adding proper fraction with like
denominators and unlike denominators
• Adding mixed numbers or fractions with
mixed numbers
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Review of Arithmetic: Fractions (cont’d)
• Comparing fractions
• Multiplying fractions
• Multiplying whole numbers and fractions
• Multiplying mixed numbers
• Multiplying a whole number and a mixed
number
• Dividing fractions
• Dividing fractions and mixed numbers
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Review of Arithmetic: Ratios
• Ratio: A way of expressing a part of a whole
or the relation of one number to another
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Review of Arithmetic: Percentages
• A percent means a part per hundred
• It can also be expressed as a fraction
– Changing a fraction to a percentage
– Changing a ratio to a percentage
– Changing a percentage into a ratio
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Review of Arithmetic: Proportions
– A proportion is a method of expressing
equality between two ratios
– Used to find an unknown quantity
– First and the last terms of the proportion
are called the extremes
– Second and the third terms of the
proportion are called the means
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Review of Arithmetic: Decimals
• A decimal is a fraction in which the
denominator is 10 or some power of 10
• Parts of a decimal: Number(s) to the left of
the decimal, decimal, number(s) to the right
of the decimal
• Types of decimals
• Reading decimals
• Adding decimals
• Subtracting decimals
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Review of Arithmetic: Decimals (cont’d)
• Multiplying a whole number by a decimal
• Multiplying decimal by a decimal
• Dividing decimals
• Changing a fraction to a decimal
• Changing a decimal to a fraction
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Calculations of Drug Dosages: Systems
of Measurement
• Nurse must be familiar with calculations of all
forms of drug dosages
• Systems of measurement:
– The metric system
– The apothecary system
– Household measurements
• Conversion between systems
• Converting within a system
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Calculations of Drug Dosages: Solutions
• Solute is a substance dissolved in a solvent
• Solutions are prepared by using a solid and a
liquid, or a liquid and a liquid
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Calculations of Drug Dosages: Reading
Drug Labels
• Drug labels give important information the
nurse must use to obtain the correct dosage
• Unit dose: A method of dispensing drugs in
which each capsule or tablet is packaged
separately
• Drug labels contain two names: Trade name,
generic name
• Dosage strength: The average strength
given to a patient as one dose
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Calculations of Drug Dosages: Oral
Dosages of Drugs
• Computed: Physician not available, written in
apothecaries’ system and label in metric
system
• Tablets and capsules
– (dose desired) / (dose in hand) = (dose
administered)
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Calculations of Drug Dosages: Parenteral
drug dosage
• Must be in liquid form before administered
• Available in three forms
– Parenteral drugs in disposable syringes or
cartridges
– Parenteral drugs in ampules and vials
– Parenteral drugs in dry form
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Calculations of Drug Dosages: Parenteral
drug dosage (cont’d)
• Calculating intravenous flow rates
• To allow IV fluid to infuse over a specified
period, the IV flow rate must be determined
• Methods of calculating intravenous flow rates
– Method 1
– Method 2
– Method 3
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Calculations of Drug Dosages: Parenteral
drug dosage (cont’d)
• Oral or parenteral drug dosages based on
weight
– The dosage may be based on the
patient’s weight
– In many instances, references give the
dosage based on the weight in kilograms
rather than pounds
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Dosage Calculations Using Dimensional
Analysis
• Procedure of calculating dosage using
dimensional analysis:
– Step 1: Identify the unit of measure to be
calculated
– Step 2: Write the identified unit of measure
to be calculated, followed by an equal sign
– Step 3: Dosage strength is written, with the
numerator always expressed in the same
unit that was identified before the equal sign
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Dosage Calculations Using Dimensional
Analysis (cont’d)
• Procedure of calculating dosage using
dimensional analysis (cont’d):
– Step 4: Write the next fraction with the
numerator having the same unit of
measure as the denominator in the
previous fraction
– Step 5: The problem is solved by
multiplication of the two fractions
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Dosage Calculations Using Dimensional
Analysis (cont’d)
• Procedure of metric conversion using
dimensional analysis:
– Step 1:Write the unit of measure to be
calculated, followed by an equal sign
– Step 2: Express the dosage strength as a
fraction with the numerator having the
same unit of measure as the number
before the equal sign
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Dosage Calculations Using Dimensional
Analysis (cont’d)
• Procedure of metric conversion using
dimensional analysis (cont’d):
– Step 3: Write the next fraction with the
numerator having the same unit of
measure as the denominator in the
previous fraction
– Step 4: Expand the equation by filling in
the missing numbers using the appropriate
equivalent
– Step 5: Solve the problem by multiplication
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Dosage Calculations Using Dimensional
Analysis: Temperatures
• Two scales used:
– Fahrenheit
– Celsius
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End of Presentation
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