Transcript Systems of Measurement in Veterinary Pharmacology Chapter 6

Systems of Measurement in
Veterinary Pharmacology
Chapter 6
Dr. Dipa Brahmbhatt VMD MpH
[email protected]
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
Household System
• Uses household measures when an approximate
dose is acceptable
• Uses a system of weights and measures based on
1 pound containing 16 fluid ounces
• Lacks standardization, but is calibrated in units
e.g. teaspoon and cup
• The drop, tablespoon, and teaspoon are the only
household measures still used in pharmacology
• Disinfectants: cups, quarts and gallon
Apothecary System
• System of liquid measure used by pharmacists; also called
the common system
• Prescription vials
• Derived from the British apothecary
system of measures
• Units in the apothecary system:
– Volume: Minim = liquid volume of a drop
of water from a standard medicine dropper
• 60 minims = 1 fluid dram
• 8 fluid dram = 1 ounce
– Weight: Grain = basic unit of weight measurement
• 1 grain of wheat = 60 mg.
• 480 grains = 1 oz = 1 oz , 12 oz = 1 lb
Metric System
• Units are based on factors of 10
• Fundamental units are meter (length), liter (volume),
and gram (weight)
• 1 mL = 1 cc = 1 g
Volume of 1 cubic centimeter of water = 1 mL water
= weighs 1 gram
• Prefixes commonly used:
–
–
–
–
Micro- = one millionth of unit = 0.000001 (10-6)
Milli- = one thousandth of unit = 0.001 (10-3)
Centi- = one hundredth of unit = 0.01 (10-2)
Kilo- = one thousand units = 1,000 (103)
Converting Within Systems
• Convert from one unit to another within the
same system
• Use of conversion factors : # used with * or /
to change a measurement from 1 unit to its
equivalent in another unit of measure
• Converting from larger to smaller units –
multiply
• Converting from smaller to larger units –
divide
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
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
From gram to miligram
Move larger
Unit to smaller
Unit hence
quantity
Is larger
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
From mg to gram
Move smaller
Unit to larger
Unit hence
quantity
Is smaller
From kilogram to grams
From grams to kilograms
From liters to mililiters
From milliliters to liters
Converting within the
Apothecary System
•
•
•
•
Using the dimensional analysis method
Determine the apothecary equivalents
Create a conversion factor
Determine what format to write the conversion factor
in
• Set up the conversion in an equation
• Perform the calculation
From dram to ounces
64 dram to ______ Ounces?
8 dr = 1 oz.
64 dr = X
X = (64 dr / 8 dr) * 1 oz. = 8 oz.
Volume: Minim = liquid volume of a drop
of water from a standard medicine dropper
60 minims = 1 fluid dram
8 fluid dram = 1 ounce
Weight: Grain = basic unit of weight measurement
1 grain of wheat = 60 mg.
480 grains = 1 oz = 1 oz , 12 oz = 1 lb
Converting within the
Household System
• Determine the household equivalents
• Create a conversion factor
• Determine what format to write the conversion factor
in
• Set up the conversions in an equation
• Perform the calculation
• Make sure the correct answer is determined by
proving the work
From cups to quarts
8 cups = ____________ qt?
1 qt = 4 cups
X = 8 cups
X = (8 cups / 4 cups) / 1 qt = 2 qt
Conversions Between Metric and
Household Systems
• Use the dimensional analysis method
• Determine the conversion factor between the two
systems
• Determine what format to write the conversion factor
• Set up the conversions into an equation
• Perform the calculation
• Make sure you have the correct answer by proving
the work
From pounds to kilogram
66 lbs = __________ kg.
1 kg = 2.2 lb
X = 66 lb
X = (66 lb / 2.2 lb) * 1 kg = 30 kg
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
A conversion factor is a number used within either
multiplication or division to change a measurement from one
unit of measurement to it’s equivalent in another unit of
measure
From grain to grams
240 gr = ____________g.
1 g = 15.4 gr
X = 240 gr
X = (240 gr / 15.4 gr) * 1 g = 31.2 g
Table 6-6
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: ratio
between the differences
– C = F – 32/1.8
– F = 1.8C + 32
From Fahrenheit to Celsius
98.6 F = ___________ Celsius
Degree Celsius = (Degree Fahrenheit – 32)/1.8
Degree Celsius = (98.6 degree Fahrenheit – 32)/ 1.8 =
37 degree Celsius