1. Systems of Measurement in Veterinary Pharmacology Chapter 6 Dr. Dipa Brahmbhatt VMD MpH dbrahmbhatt@vettechinstitute.edu

2. Systems of Measurement Household system: lacks standardization; not accurate for measuring medicine Metric system: developed in late 18th century to standardize measures and weights for European countries – Units based on factors of 10 – Prefixes denote increases or decreases in size of unit Apothecary system: system of liquid units of measure used chiefly by pharmacists

3. Household System Uses household measures when an approximate dose is acceptable Uses a system of weights and measures based on 1 pound containing 16 fluid ounces Lacks standardization, but is calibrated in units e.g. teaspoon and cup The drop, tablespoon, and teaspoon are the only household measures still used in pharmacology Disinfectants: cups, quarts and gallon

5. Apothecary System System of liquid measure used by pharmacists; also called the common system Prescription vials Derived from the British apothecary system of measures Units in the apothecary system: – Volume: Minim = liquid volume of a drop of water from a standard medicine dropper 60 minims = 1 fluid dram 8 fluid dram = 1 ounce – Weight: Grain = basic unit of weight measurement 1 grain of wheat = 60 mg. 480 grains = 1 oz = 1 oz, 12 oz = 1 lb

7. Metric System Units are based on factors of 10 Fundamental units are meter (length), liter (volume), and gram (weight) 1 mL = 1 cc = 1 g Volume of 1 cubic centimeter of water = 1 mL water = weighs 1 gram Prefixes commonly used: – Micro- = one millionth of unit = 0.000001 (10 -6 ) – Milli- = one thousandth of unit = 0.001 (10 -3 ) – Centi- = one hundredth of unit = 0.01 (10 -2 ) – Kilo- = one thousand units = 1,000 (10 3 )

10. Converting Within Systems Convert from one unit to another within the same system Use of conversion factors : # used with * or / to change a measurement from 1 unit to its equivalent in another unit of measure Converting from larger to smaller units – multiply Converting from smaller to larger units – divide

12. Converting Within the Metric System Use dimensional analysis (unit calculation) Must know metric equivalents called conversion factors Conversion factors are used to change between units and always have a value of one Cancel units to achieve answer in desired unit of measure Desired unit of measure should be on top of the conversion factor Always validate answer

13. Shortcut Method Move decimal point appropriate direction based on units Examples: – kg to g = move decimal point 3 places to the right – g to kg = move decimal point 3 place to the left – l to ml = move decimal point 3 places to the right – ml to l = move decimal point 3 places to the left

14. From gram to miligram Move larger Unit to smaller Unit hence quantity Is larger

15. Remember… When converting from larger units to smaller units, the quantity gets larger When converting from smaller units to larger units, the quantity gets smaller

16. From mg to gram Move smaller Unit to larger Unit hence quantity Is smaller

17. From kilogram to grams

18. From grams to kilograms

19. From liters to mililiters

20. From milliliters to liters

21. Converting within the Apothecary System Using the dimensional analysis method Determine the apothecary equivalents Create a conversion factor Determine what format to write the conversion factor in Set up the conversion in an equation Perform the calculation

22. From dram to ounces 64 dram to ______ Ounces? 8 dr = 1 oz. 64 dr = X X = (64 dr / 8 dr) * 1 oz. = 8 oz. Volume: Minim = liquid volume of a drop of water from a standard medicine dropper 60 minims = 1 fluid dram 8 fluid dram = 1 ounce Weight: Grain = basic unit of weight measurement 1 grain of wheat = 60 mg. 480 grains = 1 oz = 1 oz, 12 oz = 1 lb

23. Converting within the Household System Determine the household equivalents Create a conversion factor Determine what format to write the conversion factor in Set up the conversions in an equation Perform the calculation Make sure the correct answer is determined by proving the work

24. From cups to quarts 8 cups = ____________ qt? 1 qt = 4 cups X = 8 cups X = (8 cups / 4 cups) / 1 qt = 2 qt

25. Conversions Between Metric and Household Systems Use the dimensional analysis method Determine the conversion factor between the two systems Determine what format to write the conversion factor Set up the conversions into an equation Perform the calculation Make sure you have the correct answer by proving the work

26. From pounds to kilogram 66 lbs = __________ kg. 1 kg = 2.2 lb X = 66 lb X = (66 lb / 2.2 lb) * 1 kg = 30 kg

27. Conversions between Metric and Apothecary Systems At times, you may need to make conversions between systems Need relationship between two systems to serve as a bridge Bridges are found in Table 6-6 A conversion factor is a number used within either multiplication or division to change a measurement from one unit of measurement to it’s equivalent in another unit of measure

28. From grain to grams 240 gr = ____________g. 1 g = 15.4 gr X = 240 gr X = (240 gr / 15.4 gr) * 1 g = 31.2 g

29. Table 6-6

32. Temperature Conversions In the Fahrenheit system, water freezes at 32 degrees; water boils at 212 degrees In the Celsius system, water freezes at 0 degrees; water boils at 100 degrees Comparison: – 212 – 32 = 180 – 100 – 0 = 100 – 180 ÷ 100 = 1.8: ratio between the differences – C = F – 32/1.8 – F = 1.8C + 32

33. From Fahrenheit to Celsius 98.6 F = ___________ Celsius Degree Celsius = (Degree Fahrenheit – 32)/1.8 Degree Celsius = (98.6 degree Fahrenheit – 32)/ 1.8 = 37 degree Celsius