Lab 2

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LAB 2
Systems of Measurement
Systems of Measurement
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Metric system
Apothecary systems
Avoirdupois systems
THE METRIC SYSTEM
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The three primary or fundamental units in metric
system are: the meter for length, the liter for
volume, and the gram for weight.
Metric Weights
0.001 kilogram (kg)
0.01 hectogram (hg)
0.1 dekagram (dkg)
10 decigram (dg)
100 centigram (cg)
1000 milligram (mg)
1,000,000 microgram (µg)
1,000,000,000 nanogram (ng)
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1 gram (g)
1 gram (g)
1 gram (g)
1 gram (g)
1 gram (g)
1 gram (g)
1 gram (g)
1 gram (g)
Metric Volume
0.001 kiloliter (kL)
0.01 hectoliter (hL)
0.1 dekaliter (dkL)
10 deciliter (dL)
100 centiliter (cL)
1000 milliliter (mL)
1,000,000 microliter (µL)
1,000,000,000 nanoliter (nL)
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1 liter (L)
1 liter (L)
1 liter (L)
1 liter (L)
1 liter (L)
1 liter (L)
1 liter (L)
1 liter (L)
Metric Length
0.001 kilometer (km)
0.01 hectometer (hm)
0.1 dekameter (dkm)
10 decimeter (dm)
100 centimeter (cm)
1000 millimeter (mm)
1,000,000 micrometer (µm)
1,000,000,000 nanometer (nm)
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1 meter (m)
1 meter (m)
1 meter (m)
1 meter (m)
1 meter (m)
1 meter (m)
1 meter (m)
1 meter (m)
Metric Units
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General helpful guidelines:
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To prevent the mistake of overlooking a decimal
point, precede the decimal point with a zero if the
value is less than one, i.e., writing 0.8 g
To convert large unit to smaller unit, multiply
To convert small unit to larger unit, divide
To add, subtract, multiply or divide different metric
units, first convert all the units to the same
denomination.
Metric Units
Example 1:
If a chlorpheniramine maleate tablet weighs 0.26
gram, one-fourth of the same tablet weighs how
many milligrams?
Since the answer is required in milligrams, convert
the weight of the tablet into milligrams first.
0.26 g = 0.26 × 1000 = 260 mg
1/4 × 260 mg = 65 mg
answer: 65 mg
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Metric Units
Example 2:
If a vial of gentamycin contains 80 mg of drug in 2 mL,
how many micrograms of the drug are present in 0.025
mL?
80 mg = 80,000 µg
By the method of proportion, if 80,000 µg are
contained in 2 mL, how many micrograms are
contained in 0.025 mL?
80,000
2mL
X
0.025 mL
answer: X = 1000 µg
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APOTHECARIES’ SYSTEM
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Unlike the metric system which has units for
weight, volume, and length, the apothecaries’
system has units for weight and volume only.
The basic unit for weight is grain (gr) and that of
volume is minim (m). Unlike the metric units, the
amount is expressed in Roman numerals after the
apothecaries’ symbol. For example, 1⁄2 grain is
expressed as gr ss but not 1⁄2gr.
Apothecaries’ Liquid Measures.
60 minims (m)
8 fluid drams (fƷ )
16 fluid ounces (f℥ )
2 pints (O)
4 quarts (qt)
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1 fluid dram (fƷ )
1 fluid ounce (f℥ )
1 pint (pt or O)
1 quart (qt)
1 gallon (gal or C)
Apothecaries’ Weight Measures
20 grains
3 scruples
8 drams (Ʒ)
12 ounces (℥)
1 pound (lb)
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1 scruple (℈)
1 dram (Ʒ)
1 ounce (℥)
1 pound (lb)
5760 grains (gr)
APOTHECARIES’ SYSTEM
Example 1:
If a prescription calls for gr ii thyroid desiccated
tablets and the pharmacist has gr ss tablets in
stock, how many tablets of gr ss should be
provided?
gr ii = 2 grains
gr ss = ½ grain
2 ÷ ½ = 4 tablets of gr ss
answer: 4 tablets of gr ss
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APOTHECARIES’ SYSTEM
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Example 2:
How many doses of fƷiv are present in O iiss of
MaaloxR?
O iiss = 2 ½ pints
= 2.5 × 16 ounces = 40 ounces
= 40 × 8 = 320 fluidrams
= 320/4 = 80 doses
answer: 80 doses
THE AVOIRDUPOIS SYSTEM
1 ounce (oz)
1 pound (lb)
= 437.5 grains
= 7000 grains
Practice problems
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Reduce 1.23 kg to grams
Reduce 85 micrometers to centimeters
A capsule contains the following amounts of
medicinal substance: 0.075 g, 20 mg, 0.0005 g, and
500 µg. What is the total weight of the substances
in the capsule.
Multiply 820 mL by 12.5 and express the result in
liters.
Practice problems
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If an injectable solution contains 25 µg of a drug
substance in each 0.5 mL. How many mL will be
required to provide a patient with 0.25 mg of the
drug substance.
Convert 2 ½ pt to C
Convert 2.5 qt to f℥
How many f℥ii-bottles of cough syrup can be
optained from 5 gallons of the cough syrup?
Practice problems
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Aspirin tablets contain 325 mg of aspirin. How may be
prepared from 5 kg of aspirin?
How many 15-minim doses can be obtained from a
mixture containing f℥iii of one ingredient and fƷii of
another?
A formula contains ℈ii of ingredient A, Ʒi of ingredient
B, Ʒiv of ingredient C, and gr viiss of ingredient D.
calculate the total wieght of the ingredients.
If a drug costs 8SR per oz (avoir), what is the cost of
Ʒii?
Home work
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A vitamin capsule contains 6.25 µg of vitamin
B12. how many capsules can be prepared from 1 g
of vitamin B12.
Convert 6.2 g to ng.
A pharmacist had 1 gallon of phenobarbital elixir.
At different time he dispensed Oi, f℥vi, fƷiv, Oss,
f℥iss and f℥xii. What volume in fluidounces, of the
elixir was left?

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