Systems of Measurements (1)
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Transcript of Systems of Measurements (1)
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Marie Azeneth A. Josol, RPh
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The metric system is the internationally
accepted system of weights and measures and
is the official system of the United States
Pharmacopeia (USP) and National Formulary
(NF).
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The base units (the primary units of
measurement) of the metric system are gram
for weight, liter for volume, and meter for
length. In this system, prefixes are used to show
which portion of the base unit is being
considered. It is important that you learn the
most commonly used prefixes.
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SI METRIC SYSTEM
UNIT ABBREVIATION EQUIVALENTS
WEIGHT gram (base unit) g 1 g = 1000 mgmilligram mg 1 mg = 1000 mcg = 0.001 gmicrogram mcg (or g) 1mcg = 0.001 mg = 0.000001gkilogram kg 1 kg = 1000 g
VOLUME liter ( base unit ) L ( or ) 1 L = 1000 mlmilliliter mL ( or m ) 1 ml = 1cc = 0.001 Lcubic centimeter cc 1 cc = 1 ml = 0.001 L
LENGTH meter ( base unit ) m 1 m = 100 cm = 1000 mmcentimeter cm 1 cm = 0.01 m = 10 mmmillimeter mm 1mm = 0.001 m = 0.1 cm
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EXAMPLE 1 :
Convert: 0.3 g to mg Equivalent: 1 g = 1000 mg. Conversion
factor is 1000
THINK: Larger to smaller: (x)
Multiply by 1000 0.3 x 1000 = 300 mg
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EXAMPLE 2 :
Convert 5000 mL to L Equivalent: 1L = 1000 mL. Conversion
factor is 1000
THINK: Smaller to larger : ()
Divide by 1000 5000 () 1000 = 5L
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common systems ofmeasurement include the
apothecaries system and the
avoirdupois system.
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The apothecaries system is the traditional
and historic system of weights and measures
used in pharmacy.
system is expressed by unique units and
symbols, namely the minims (m ), grain (gr.),scruple (), drachm or dram (), ounce (0z),
pound (lb.).
The avoirdupois system uses the three unitsof weight, the grain (gr), ounce (oz), and
pound (lb.).
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Conversion Equivalents of Length
1 meter (m) = 39.37 in
1 inch (in) = 2.54 cm
Conversion Equivalents of Volume1 fluidounce (f3) = 29.57 mL = 30 mL
1 pint (pt) = 473 mL
1 gallon (US) = 3785 mL
1 gallon (US) = 128 f3Conversion Equivalents of Weight
1 gram (g) = 15.432 gr
1 kilogram (Kg) = 2.2 lb
1 grain (gr) = 0.065 g or 65 mg1 oz ( 437.5 gr ) = 28.35 g
1 lb ( 7,000 gr ) = 454 g
Common Household Equivalents
1 teaspoon ( tsp or t ) = 5 mL
1 tablespoon ( tbsp or T ) = 15 mL
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The apothecary system was the first
system of medication measurement used
by pharmacists and physicians.
The grain (gr) has the same value of
weight in both the apothecaries andavoirdupois systems.
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Convert each of the following:
6.35 mm to inches
2.5 L to fluidounces
12.5 g to grains 6.5 grains to milligrams
2 pt. to milliliters
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A nurse telephones a pharmacy regarding
the proper quantity of an injection to
administer to a pediatric patient from a 1
ml vial contaiing 0.1mg of digoxin. The
attending physician had prescribed a doseof 25mcg. How many ml should be the
pharmacists response?
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A hospital pharmacist is asked to prepare an
intravenous infusion of dopamine. Based on the
patients weight the pharmacist calculate a doseof 500mcg/min. for continuous infusion. The
concentration of the infusion is 400mcg/250ml.
What is the concentration of the infusion on
mcg/ml basis? How many ml of dopamine is thepatient to receive in the first hour treatment?
How long will infusion last?
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Case 1:
0.1mg/ml= 100mcg/ml
35 mcg X 1ml/100mcg=1/4ml or 2.5ml
Case 2:
Conc. Of infusion, mcg/ml
400mg= 400,000mcg
400mg:250ml =400,000mcg/250ml=1600mcg/ml
Mg, dopamine 1st hour
500mcg/1min X 60 min/Hr X1mg/1000mcg
= 30mg/hour
Infusion duration
400mg X 1min/500mcg X1000mcg/1mg = 800min or 13hour and 20 mins.
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e.g :Convert 140F to C:
5F = 9C + 160 (formula)
5(140) = 9C + 160
700 = 9C + 160700 - 160 = 9C
540 = 9C
60 = C