focus on pharmacology essentials for health professionals chapter measurement systems and their...

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PHARMACOLOGYPHARMACOLOGYESSENTIALS FOR HEALTH PROFESSIONALS

CHAPTER

Measurement Systems and Their Equivalents

6

Focus on Pharmacology: Essentials for Health Professionals, Second EditionJahangir Moini

Knowledge and AccuracyKnowledge and Accuracy

• Healthcare professionals who deal with administration of medications must be:– Knowledgeable of weights and measures– Accurate in calculations– Careful in checking and verifying

calculations


Units of MeasureUnits of Measure

• Pharmacology uses 3 systems of measurement:– Metric: most common, most accurate, and

safest– Apothecary: older system– Household: less accurate


Metric SystemMetric System

• Based on decimals• Gram (g): unit of weight• Liter (L): unit of volume• Meter (m): unit of length• Prefixes denote multiples or fractions

of 10


Metric Prefixes (Latin)Metric Prefixes (Latin)

0.1 or 1/10deci- (d)

0.01 or 1/100centi- (c)

0.001 or 1/1,000milli- (m)

0.000001 or 1/1,000,000micro- (mc)

ValuePrefix


Metric Prefixes (Greek)Metric Prefixes (Greek)

1,000,000mega- (M)

1,000kilo- (k)

100hecto- (h)

10deca- (da)

ValuePrefix


Metric SystemMetric System

1 cm = 10 mm Length

1 L = 1,000 mLVolume

1 kg = 1,000 g

1 mg = 1,000 mcg = 0.001 g

1 g = 1,000 mgWeight


Système International (SI)Système International (SI)

• Internationalized system of measurement based on gram for weight, liter for volume, and meter for length.– 1 g = 1,000 mg = 1,000,000 mcg– 1 L = 1,000 mL– 1 m = 100 cm = 1,000 mm


Apothecary SystemApothecary System

• Apothecary system measures volume in:– Minims (basic unit), drams (fluidrams),

ounces, (fluidounces), pints (volume), quarts, gallons

• Apothecary system measures weight in:– Grains (basic unit)


Apothecary SystemApothecary System

• Apothecary system is used for only a few drugs (acetaminophen, aspirin, and phenobarbital).


Apothecary MeasurementsApothecary Measurements

gallon (gal)quart (qt) = pt ii

pint (pt) = qti = 0 32pound (lb) fluid ounce ( )℥ = pti = 16℥ounce (oz or ) ℥

fluiddram (fl dr)dram (dr or ℨ)

Minim ( ) ♏grain (gr)

VolumeWeight


Household SystemHousehold System

• Household system used in most American homes but is not accurate.

• Only household units used in measuring drugs are units of volume: – Drop– Tablespoon – Cup– Quart

– Teaspoon– Ounce (fluid)– Pint– Gallon


Household MeasurementsHousehold Measurements

drop (gtt) 15 gtt = 1 mL

teaspoon (tsp) 1 tsp = 5 mL

tablespoon (T) 1 T = 3 tsp

ounce (oz) 1 oz = 2 T

cup 1 cup = 8 oz

pint (pt) 1 pt = 2 cups

quart (qt) 1 qt = 4 cups = 2 pt

gallon (gal) 1 gal = 4 qt


MilliequivalentsMilliequivalents

• Milliequivalents (mEq): used to indicate strength of certain drugs– Defined as number of grams of equivalent

weight of a drug contained in 1 mL of normal solution

– Some drugs measured in mEq include potassium chloride, sodium bicarbonate, sodium chloride


Units and International UnitsUnits and International Units

• Units mainly measure potency of heparin, insulin, penicillin, and some vitamins.

• International Units (IU) are used to measure vitamins.– Standardized by international agreement

• Units and mEq cannot be directly converted into the metric, apothecary, or household systems.


Conversion Within and Between Conversion Within and Between Measurement SystemsMeasurement Systems

• Drug doses are usually ordered in metric grams, milligrams, liters, and milliliters.

• You must know how to convert between systems and within systems.


Approximate Volume EquivalentsApproximate Volume Equivalents

2 pt = 1 qt32 oz960 mL

2 cups = 1 pt16 oz480 mL

8 oz = 1 cup8 oz240 mL

2 T = 1 oz1 oz30 mL

1 T3–4 dr15 mL

1 tsp1 dr5 mL

HouseholdApothecaryMetric


Approximate Weight EquivalentsApproximate Weight Equivalents

220 lb1 kg

2.2 lb, gr xv, 15 gr1 g (1,000 mg)

gr vii ss (7-1/2 gr)0.5 g

gr i (1 gr)60 mg

gr 1/230 mg

gr 1/415 mg

gr 1/601 mg

ApothecaryMetric


Temperature ConversionTemperature Conversion

• Two common scales measure temperature: Celsius (C) and Fahrenheit (F).

• Fahrenheit is used mostly in the U.S.; Celsius is used elsewhere.

• Water freezes at 0°C, and at 32°F.• Water boils at 100°C and at 212°F.


Converting from Converting from Fahrenheit to CelsiusFahrenheit to Celsius

• (°C x 1.8) + 32 = °F • (°F – 32) × 1.8 = °C OR• (°F – 32) × 5/9 = °C


Figure 6-1 Thermometer showing the temperatures at which water freezes (0°C and 32°F) and boils (100°C and 212°F).

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