Chapter 10 Objectives Convert among apothecary, household, and metric measurement systems Use the correct number formats for the measurement systems Properly format the answers

Apothecary Measurement and Conversion This unit brings together the fundamental skills of the previous chapters & applies these basics to health care applications. Although new information is taught, the processes for arriving at the correct answers depend on your ability to compute using fractions, decimals, ratio, & proportion &, to a lesser degree, percents. This unit will cover the apothecary measurements & two methods of performing apothecary. These fundamentals will help prepare you for math applications in the health care professions. Unit 10

Page 218 Overview This unit brings together the fundamental skill of the previous units and applies these basics to health care situations. Although you will learn new information in this unit, processes for arriving at the correct answers depend on your ability to compute using fraction, decimals, ratios, proportions, and, to a lesser degree, percents. This unit will cover apothecary measurements and two methods of converting among measurement systems. These fundamentals will help prepare you for math applications in the health care profession.

Apothecary Measurement and Conversion Page 219 Apothecary Measurement and Conversion The apothecary system is an old measurement system that originated in England. It relies on several number systems to denote measurements: lower case Roman numerals, Arabic numerals, and fractions. This system is being replaced by metric units to make the measuring system more uniform and avoid medication errors Some physicians still use this system as a matter of habit so you may see labels, prescriptions, and doctors’ orders using some of these units. This system, which uses grains fro weight and minims for volume, is used by physicians and pharmacists to calculate drug amounts.

Apothecary Measurement and Conversion (Cont’d) Page 220 Apothecary Measurement and Conversion (Cont’d) The apothecary system uses some basic rules that do not exist in other measurement systems. These rules include: Fractions of ½ may be written as ss. Lower case Roman numerals are used for apothecary amounts of ten or less and for the numbers 20 and 30. The symbol is placed before the quantity: Thus, grains 7 ½ is written as grains viiss or gr. viiss Apothecary system works with approximate equivalents!

Apothecary Measurement and Conversion (Cont’d) Page 220 Apothecary Measurement and Conversion (Cont’d) Approximate Equivalents 1 teaspoon = 5 milliliters grain i = 65 milligrams grain i = 1 drop Fluid ounce 1 = 8 teaspoons Fluid ounce 1 = 2 tablespoons Fluid ounce 1 = 30 milliliters 1 inch = 2.54 centimeters 1 kilogram = 2.2 pounds 1 teaspoon = 60 drops 1 pint = 2 cups 1 quart = fluid ounces 32 1quart = 1 liter 1 cup = 240 milliliters Example – page 223 – practice 1: even Group Work – page 223 – practice 1: odd

Multiple Conversions Page 223 When completing multiple conversions, it is best to work within the same unit of measure before changing to another unit of measure. For example, do all of the metric conversions, and then move to the grain conversions; or make the grain-to-metric conversion into milligrams, and then convert from milligrams to grams or micrograms. Example – page 224-225 – practice 2-3: even Group Work – page 224-225 – practice 2-3: odd

Converting Liquid Equivalents Page 225 Converting Liquid Equivalents You will convert liquid equivalents in the same manner, using ratio and proportion or dimensional analysis. You will need a wider range of conversions to convert liquid equivalents. Rely on the conversion charts, but work toward memorizing these equivalents so that you cane efficiently apply them. Example – page 225-229 – practice 4-6: even Group Work – page 225-229 – practice 4-6: odd

Rounding in Dosage Calculations Page 229 Rounding in Dosage Calculations The metric system is used to measure liquids, weights, and medicine. Rounding will make dealing with the applications more practical. To assist in this process, follow these five guidelines: Any decimal number that stands along without a whole number must have a 0 placed in the whole number place. Round decimals to the correct place value. This is somewhat dependent on your profession (for our class two decimal places).

Rounding in Dosage Calculations (Cont’d) Page 229 Rounding in Dosage Calculations (Cont’d) If the drug measurement is in metrics, the solution to the problem must be in decimals (apothecary must be in fractions). Round only when you reach your final answer. Of note are pediatric doses, which are rounded down, not up, to avoid overdosing. The same principle is used with adults for high-alert drugs. In some cases, it is important to place as zero at the end of the number. The trailing zero is used to show the exact level of a value such as a label result, the size of a lesion, or a catheter size. 4. Do not over-round. In medications, a small amount of medication can be critical in dosing. If you begin to round as you set up the problem, you may round again when you finalize the problem, and this can skew the dosage amount. *** Example – page 230 – practice 7-8: even Group Work – page 230 – practice 7-8: odd