Measurement and Dosage Calculation
-Fraction- way of expressing an amount that is part of a whole
-Numerator- the top number of a fraction
-Denominator- the bottom number of the fraction
-Simplifying fractions- to reduce a fraction to its lowest terms
-Multiplying fractions- multiply numerator by numerator and denominator
by denominator
-Dividing fractions- invert (flip over) the divisor, then multiply the two
fractions
-Decimal fractions- fractions expressed as decimals
-Refer to pages 36-40 for math review
-Dosage range- different amounts that can produce therapeutic effects
-Convert- change from one unit or system to another in the course of your
daily routine
-System of measurements
-Apothecary system- a very old an infrequently used
-Grain (gr) - basic unit of weight
-Minim (m) - basic unit of volume
-Dosage quantities are written in lowercase roman numerals
-Fractions are expressed in Arabic numerals rather than
decimals
-Metric system
-Meter- unit of length
-Liter- volume
-Gram- weight
-Prefixes- indicate smaller or larger units in the system
-Kilo- 1000
-Hect- 100
-Deca- 10
-Deci- 1/10
-Centi- 1/100th
-Milli- 1/1000th
-Micro- 1/1000000th
-1cc = 1ml
-Household system
-Weight- Ounce, pound, and ton
-Volume- Drop, drops, teaspoon, tablespoon, teacup, cup, pint,
quart, and gallon
-Equivalents
-16 ounces = 1 pound
-3 teaspoon = 1 tablespoon = ½ ounce
-16 tablespoons = 1 cup = 8 fluid ounces
-2 cups = 1 pint
-2 pints = 1 quart
-4 quarts = 1 gallon
-Temperature scales
-Fahrenheit- 32 degrees is the freezing point of water and 212 degrees
is the boiling point of water
-Celsius- 0 degrees is the freezing point of water and 100 degrees is
the boiling point of water
-Conversion between Fahrenheit and Celsius
- Fo = 1.8 Co + 32
- Co = (Fo – 32) / 1.8
-Converting among measurement systems- can be accomplished, refer to
page 47, table 3.8 and 3.9
-Drug calculation
- Calculating the number of tablets, capsules, and milliliters
- Want / have
-Want- desired dose
-Have- available dose per tablet
- Dosage calculations with conversions
- (Dosage in ordered unit) x (conversion fraction) = (dose in
desired unit)
-Refer to page 50-51
-Children’s doses
- Adjusting doses by age
- (Patient’s age, in months) x (usual adult dose) / (adult
age, always 150 in months) = (child’s dose)
-Refer to page 52
- Adjusting doses by weight
- (Patient’s weight) x (usual adult does) / (adult weight,
always 150 lbs) = child’s dose
-Refer to page 52
- Parenteral therapy
- (Order amount to be delivered/ total time of delivery) x
(tubing drop factor / 1 cc) x (1 hour / 60 minutes) = drops
a minute
-Refer to pages 52-53