Systems of Measurements (1)

8/6/2019 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

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