The Apothecary & Household System of MeasurementMs. RyanMCATCMecial Math2015-2016

Apothecary System

• An old system of measurement• First used by apothecaries (early pharmacists)

and moved from Europe to colonial America• Household system evolved from the apothecary

system• Older medications are still measured in

apothecary units

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Apothecary System Terms

• Dram – common unit of volume in the apothecary

• Grain (gr) – basic unit

• Minim – common unit of volume

• Ounce – fluid ounces of volume

• Unit (USP Unit) – amount of medication to produce an effect

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Apothecary System

ERROR ALERT!

Do not confuse grains and grams.• grains (gr)• grams (g)

• 1 gr = 60 mg = 0.06 g

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The basic unit of weight is the grain (gr).

Apothecary System

ERROR ALERT!• Do not confuse the symbols for drams and ounces.• 1 ounce ( ) = 8 drams ( )

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The three common units of volume are minim ( ) dram ( ) ounce ( )

Apothecary System• Apothecary ounce is used in the United States.• 8 ounces to a cup is commonly used in the home

to measure liquids.• The dram is most frequently used to

abbreviate teaspoonful which is nearly the same volume.

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Apothecary Notation Rule

When writing a value in the apothecary system:

1. If a value is less than 1, write it as a fraction. 2. Unless the value is one-half, write it as the

abbreviation ss.3. Write the values with lowercase Roman numerals. 4. Write the abbreviation, symbol or unit before the

quantity.

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Examples for Practice

1. Write four grains using apothecary notation.

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2. Write two and one-half grains using apothecary notation.

gr iv or gr iv

gr iiss

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3. Write twelve ounces using apothecary

notation.

The Household Measurement System• Used in homes, particularly in kitchens, in the United

States. • The units of household measure for volume include

teaspoonful, tablespoonful, cup, pint, quart, and gallon. • The units of household measure for weight are pounds and

ounces. • Measuring volume using the household measure is less

accurate than using other systems because the measuring utensils can vary in size.

• Nevertheless, household volume measure may be used in community pharmacy practice when dispensing drugs that will be administered in the patient’s home because patients may have other measuring devices at home.

• Labels instructing patients on how to take a medication often use household measure units for this reason.

Apothecary and Household Equivalents

• It is important to note that the fluid ounce is the same in household and in apothecary (pharmacy) volume measure.

• However, the ounces used to signify weight are different. • There are 12 oz in an apothecary pound, while there are 16

oz in a household pound. • The household pound is the more commonly used

equivalence.• Apothecary ounces = household ounces• Neither bases on multiples of 10

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Abbreviations for Household Measures

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Unit of Measurement

Abbreviations

drop gt or gtt (plural)

teaspoon tsp or t

tablespoon tbsp or T

ounce oz or

Abbreviations for Household Measures

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Unit of Measurement

Abbreviation

cup c

pint pt

quart qt

gallon gal

Examples for Practice

Write the quantity in Arabic numerals before the abbreviation for the unit.

• Example: Write six drops using household notation.• 6 gtt

• Example: Write twelve ounces using household notation.• 12 oz

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Apothecary and Household Equivalent Measures

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drop (gtt) 1 drop = 1 minim

teaspoon (tsp or t)

1 teaspoon = 60 drops

tablespoon (T)

1 tablespoon = 3 teaspoons

ounce (oz) 1 ounce = 2 tablespoons

cup (c) 1 cup = 8 ounces

Milliequivalents and Units

• Milliequivalents (mEq)• The mEq is defined as of an equivalent weight of a

chemical.

• Sodium and potassium are often measured in mEq.

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• USP Units (U)• Medications such as insulin, heparin, and

penicillin are measured in units (U).• Size of the Unit varies for each drug.

Converting Among Metric, Apothecary, and Household Systems

• When calculating drug dosages, you must often convert among the metric, apothecary, and household systems.

• You need to know how the measure of a quantity in one system compares to its measure in another system.

1 tsp = 5 mL = 5 cc

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