Transcript No Slide Title

Fundamentals of Pharmacology for Veterinary Technicians 6
Submitted by Callie Parr and used in cooperation with the University of Illinois at UrbanaChampaign.
The materials that appear in this document may be freely reproduced for educational/training
activities. There is no requirement to obtain special permission for such uses. We do,
however, ask that the following statement appear on all reproductions:
FUNDAMENTALS OF PHARMACOLOGY FOR VETERINARY TECHNICIANS 6, by THOMPSON
DELMAR LEARNING
Materials produced for classroom use in conjunction with permission from the University of
Illinois Agricultural Education Program.
This permission statement is limited to the reproduction of material for educational/training
events. Systematic or large-scale reproduction or distribution (more than one hundred
copies per year)—or inclusion of items in publications for sale—may be done only with
prior written permission. Also, reproduction on computer disk or by any other electronic
means requires prior written permission. Contact the University of Illinois Agricultural
Education Program to obtain special permission.
The University of Illinois and its affiliated entities, in addition to the individual submitting the
materials, assumes no liability to original work or activities therein.
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Fundamentals of Pharmacology
for Veterinary Technicians
Chapter 6
Systems of Measurement
in Veterinary Pharmacology
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Systems of Measurement
• Household system: lacks standardization;
not accurate for measuring medicine
• Metric system: developed in late 18th
century to standardize measures and
weights for European countries
– Units based on factors of 10
– Prefixes denote increases or decreases in size
of unit
• Apothecary system: system of liquid units
of measure used chiefly by pharmacists
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Metric System
• Units are based on factors of 10
• Base units are meter (length), liter
(volume), and gram (weight)
• Prefixes commonly used:
– Micro- = one millionth of unit =
0.000001
– Milli- = one thousandth of unit = 0.001
– Centi- = one hundredth of unit = 0.01
– Kilo- = one thousand units = 1,000
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Converting Within the Metric
System
• Use dimensional analysis (unit calculation)
• Must know metric equivalents called conversion
factors
• Conversion factors are used to change between
units and always have a value of one
• Cancel units to achieve answer in desired unit of
measure
• Desired unit of measure should be on top of the
conversion factor
• Always validate answer
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Shortcut Method
• Move decimal point appropriate direction
based on units
• Examples:
– kg to g = move decimal point 3 places to the
right
– g to kg = move decimal point 3 place to the left
– l to ml = move decimal point 3 places to the
right
– ml to l = move decimal point 3 places to the
left
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Remember . . .
• When converting from larger units to
smaller units, the quantity gets larger
• When converting from smaller units
to larger units, the quantity gets
smaller
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Apothecary System
• System of liquid measure used by
pharmacists; also called the common
system
• Derived from the British apothecary
system of measures
• Units in the apothecary system:
– Minim = liquid volume of a drop of water from
a standard medicine dropper
• 60 minims = 1 fluid dram
– Grain = basic unit of weight measurement
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Conversions between Metric
and Apothecary Systems
• At times, you may need to make
conversions between systems
• Need relationship between two
systems to serve as a bridge
• Bridges are found in Table 6-6
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Temperature Conversions
• In the Fahrenheit system, water freezes at
32 degrees; water boils at 212 degrees
• In the Celsius system, water freezes at 0
degrees; water boils at 100 degrees
• Comparison:
–
–
–
–
–
212 – 32 = 180
100 – 0 = 100
180 ÷ 100 = 1.8
C = F – 32/ 1.8
F = 1.8C + 32
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Dose Calculations
• Must know correct amount of drug to
administer to a patient
• Must be in same system of measurement
• Weight conversion factor: 2.2 lb = 1 kg
• Remember that drugs can be measured in
mcg, mg, g, gr, ml, l, units
• Remember that drugs can be dispensed
or administered in tablets, ml, l, capsules
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Solutions
• Solutions are mixtures of substances not
chemically combined with each other
– The dissolving substance of a solution is
referred to as the solvent (liquid)
– The dissolved substance of a solution is
referred to as the solute (solid or particles)
– Substances that form solutions are called
miscible
– Substances that do not form solutions are
called immiscible
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Working with Solutions
• The amount of solute dissolved in solvent
is known as the concentration
• Concentrations may be expressed as
parts (per some amount), weight per
volume, volume per volume, and weight
per weight
• Usually reported out as percents or
percent solution
• Remember that a percent is the parts per
the total times 100
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Rules of Thumb When Working
with Solutions
• Parts: parts per million means 1 mg of
solute in a kg (or l) of solvent (1:1000)
• Liquid in liquid: the percent concentration
is the volume per 100 volumes of the total
mixture (1 ml/100 ml)
• Solids in solids: the percent concentration
is the weight per 100 weights of total
mixture (60 mg/100 mg)
• Solids in liquid: the percent concentration
is the weight in grams per 100 volume
parts in milliliters (dextrose 5% = 5
g/100ml)
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Percent Concentration
Calculations
• Pure drugs are substances that are 100% pure
• Stock solution is a relatively concentrated
solution from which more dilute solutions are
made
• Ratio-proportion method: one method of
determining the amount of pure drug needed to
make a solution
– Amount of drug/amount of finished solution = % of
finished solution/100% (based on a pure drug)
• Remember that the amount of drug used to
prepare a solution is added to the total volume of
the solvent
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Another Way to Determine
Volume
Volume concentration method:
• Vs = volume of the beginning or stock
solution
• Cs = concentration of the beginning or
stock solution
• Vd = volume of the final solution
• C d = concentration of the final solution
Vs x Cs = Vd x Cd
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Drug Concentrations in
Percents
• Drug concentrations are sometimes listed
in percents
• Parts per total = parts (in g) per 100
• The front of the vial specifies the
concentration (for example, 2% lidocaine)
• Use X g/100 ml to determine dose
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Reconstitution Problems
• Drug is in powder form because it is not
stable when suspended in solution
• Such a drug must be reconstituted (liquid
must be added to it)
• The label should state how much liquid to
add
• Powder may add to the total final volume
of liquid being reconstituted
• Label a reconstituted drug with the date
prepared, the concentration, and your
initials
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Additional Practice
• Check the book, CD-ROM, and on-line
material for calculation problems
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.