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Introduction to Pharmaceutical Calculation

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Units of measurement and metric conversion Measurement is the process of obtaining quantitative information about the physical world. Unit of measurement any division of quantity accepted as a standard of measurement or exchange.

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Units of measurement used in Pharmacy 1. Avoirdupois System mainly used in measuring bulk medication encountered in manufacturing. Commonly used to measure weight Standard measure for weight is grain (gr) PoundOuncesGrains (lb)(oz)(gr) 1 =16 = 7000 1 = 437.5

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Units of measurement used in Pharmacy 2.Apothecary System Commonly used for prescribing and dispensing medication Commonly used for measuring volume Standard of measure for weight is grain (gr) Standard of measure for volume is minim ( )

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Apothecary System Weight PoundOuncesDramsScruplesGrain (lb)( ) ( ʒ )( )(gr) 1 =12 =96 = 288 = 5760 1 =8 =24 =480 1 =3 = 60 1 =20

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Apothecary System Volume Gallons PintsFluidFluidMinims OuncesDrams (gal)(pt) ( f )(f ʒ )( ) 1 =8 =128 =1024 = 61,440 1 =16 =128 =7,680 1 = 8 =480 1 =60

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Units of measurement used in Pharmacy 3.Metric System is based on the decimal system in which everything is measured in multiples or fractions of 10. major systems of weights and measurement used in medicine. Uses standard measures: Gram for weight (g) Liter for volume (l) Meter for length or distance (m)

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Metric conversion process of restating a metric measurement in a larger or smaller metric unit of measurement. Ex: converting from kilograms to grams Metric units are denoted by prefixes Greek prefixes- multiplier Latin prefixes - fractions of the base unit

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Metric conversion Tips: 1. Understand the different units of measurement and what they measure (example: gram for weight). 2. Memorize the relationship between the units of measurements 1 kg = 1000 g. 3. Know where to move the decimal point to convert accurately.

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UnitAbbrevia- tion FractionExponentDecimalWord Micromc 1/1,000,000 10 -6 0.000001Millionth Millim1/1,00010 -3 0.001Thousandth Centic1/10010 -2 0.01Hundredth Decid1/1010 -1 0.1Tenth Base unitg,m,l110 0 1One Dekada1010 1 10Ten Hectoh10010 2 100Hundred Kilok100010 3 1000Thousand

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Prefixes with Standard Measures Length: standard measure is meter 1 kilometer (km) = 1000 meters (m) 1 meter (m) = 100 centimeters (cm) 1 centimeter (cm) = 1 millimeter(mm) 1 meter (m) = 1000 millimeter (mm)

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Prefixes with Standard Measures Volume: the standard measure is liter (L) 1 Liter (L) = 1000 milliliter (ml) 1 Deciliter = 100 milliliter (ml) 1 Centiliter = 10 milliliter (ml) 1 Liter = 1, 000, 000 microliter (mcl) 10 Deciliter = 1 liter (L) 100 Centiliter = 1 liter (L)

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Prefixes with Standard Measures Weight: Standard measure is gram (g) 1 Kilogram (kg) = 1000 grams (g) 1 Gram (g) = 1000 milligrams (mg) 1 Centigram (cg) = 10 milligrams (mg) 1 Decigram (dg) = 100 milligrams (mg) 1 milligram (mg) = 1,000 micrograms (mcg) 1 gram (g) = 1,000,000 micrograms (mcg)

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Prefixes with Standard Measures Length : Standard measure is meter (m) 1 Kilometer = 1000 meters (m) 1 Meter (m) = 100 centimeter (cm) 1 Meter (m) = 10 decimeter (dm) 1 Meter (m) = 1000 millimeter (mm)

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Conversion Example 1: How many minims are there in 25 fluid ounces? 25 fl x 8 fl ʒ x 60 = 12,000 1 fl 1 fl ʒ

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Example 2: How many ounces are 465 scruples? 465 x 1 ʒ x 1 = 19.375 3 8 ʒ

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Convert the following 1.30 ml = _________ fluid ounces 2.855 ml = ________ pints 3.92 gr = _________ ounces (apothecary) 4.2.8 kg = ________ mg 5.75 cm = ________ dm 6.6 km = _________ cm 7.453 mm = _______ m

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Convert the following 8. 0.00085 dg = _________ mcg 9. 100 mm = ___________ cm 10. 15 km = ___________m 11. 2,846,230 mcl = ______L 12. 2 kg = _____________cg 13. 56,000 mm = ________km 14. 5 kg = ______________dg

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Sample Problems 1.The prescription order calls for preparation of 1.5g of menthol and salicylic acid (equal quantity) in an ointment base. Express the quantity of each ingredients in mg.

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Sample Problems 2. Abdul Azziz needs to take Amoxicillin 500mg 1 capsule 3 times per day for 7 days to treat his chest infection. How much amoxicillin will he consume during the course of antibiotic treatment? Express the answer in grams (g).

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Temperature Scales of Temperature Measurement 1. Celsius – °C - also known as Centigrade - scale was devised by dividing the range of temperature between the freezing and boiling temperatures of pure water at standard atmospheric conditions (sea level pressure) into 100 equal parts

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2. Fahrenheit – °F -non-metric temperature scale was devised and evolved over time so that the freezing and boiling temperatures of water are whole numbers, but not round numbers as in the Celsius temperature scale.

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3. Kelvin – K - temperature scale is an extension of the degree Celsius scale down to absolute zero, a hypothetical temperature characterized by a complete absence of heat energy.

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Mathematical Formula for Conversion Celsius to Fahrenheit : F = C x (9/5) + 32 Fahrenheit to Celsius: C = (F - 32) x (5/9) Celsius to Kelvin: K = degree Celsius + 273.15 Kelvin to Celsius: Celsius = K - 273.15

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Sample Problems 1.Convert 35°C to °F Formula : F = C x (9/5) + 32 ° F = 35 x (9/5) + 32 = 35 x 1.8 + 32 = 95 °F 2.Convert 112 ° F to °C ° C = (F - 32) x (5/9) = (112 F – 32) x 0.55 = 44 ° C

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Common Pharmaceutical Equivalents Solids 1 ounce (oz) = 28.35 g 1 pound (lb) = 454 g 1 kilogram = 2.2 lbs Liquids 1 gallon = 3785 ml 1 quart = 946 ml 1 pint = 473 ml 1 fluid ounce (fl) = 29.57 ml, rounded to 30 ml 1 teaspoonful (tsp ) = 5 ml 1 tablespoonful (tbsp )= 15 ml 1 milliliter (ml) = 20 drops (gtts)

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