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LAB 2 Systems of Measurement Systems of Measurement Metric system Apothecary systems Avoirdupois systems THE METRIC SYSTEM The three primary or fundamental units in metric system are: the meter for length, the liter for volume, and the gram for weight. Metric Weights 0.001 kilogram (kg) 0.01 hectogram (hg) 0.1 dekagram (dkg) 10 decigram (dg) 100 centigram (cg) 1000 milligram (mg) 1,000,000 microgram (µg) 1,000,000,000 nanogram (ng) = = = = = = = = 1 gram (g) 1 gram (g) 1 gram (g) 1 gram (g) 1 gram (g) 1 gram (g) 1 gram (g) 1 gram (g) Metric Volume 0.001 kiloliter (kL) 0.01 hectoliter (hL) 0.1 dekaliter (dkL) 10 deciliter (dL) 100 centiliter (cL) 1000 milliliter (mL) 1,000,000 microliter (µL) 1,000,000,000 nanoliter (nL) = = = = = = = = 1 liter (L) 1 liter (L) 1 liter (L) 1 liter (L) 1 liter (L) 1 liter (L) 1 liter (L) 1 liter (L) Metric Length 0.001 kilometer (km) 0.01 hectometer (hm) 0.1 dekameter (dkm) 10 decimeter (dm) 100 centimeter (cm) 1000 millimeter (mm) 1,000,000 micrometer (µm) 1,000,000,000 nanometer (nm) = = = = = = = = 1 meter (m) 1 meter (m) 1 meter (m) 1 meter (m) 1 meter (m) 1 meter (m) 1 meter (m) 1 meter (m) Metric Units General helpful guidelines: 1. 2. 3. 4. To prevent the mistake of overlooking a decimal point, precede the decimal point with a zero if the value is less than one, i.e., writing 0.8 g To convert large unit to smaller unit, multiply To convert small unit to larger unit, divide To add, subtract, multiply or divide different metric units, first convert all the units to the same denomination. Metric Units Example 1: If a chlorpheniramine maleate tablet weighs 0.26 gram, one-fourth of the same tablet weighs how many milligrams? Since the answer is required in milligrams, convert the weight of the tablet into milligrams first. 0.26 g = 0.26 × 1000 = 260 mg 1/4 × 260 mg = 65 mg answer: 65 mg Metric Units Example 2: If a vial of gentamycin contains 80 mg of drug in 2 mL, how many micrograms of the drug are present in 0.025 mL? 80 mg = 80,000 µg By the method of proportion, if 80,000 µg are contained in 2 mL, how many micrograms are contained in 0.025 mL? 80,000 2mL X 0.025 mL answer: X = 1000 µg APOTHECARIES’ SYSTEM Unlike the metric system which has units for weight, volume, and length, the apothecaries’ system has units for weight and volume only. The basic unit for weight is grain (gr) and that of volume is minim (m). Unlike the metric units, the amount is expressed in Roman numerals after the apothecaries’ symbol. For example, 1⁄2 grain is expressed as gr ss but not 1⁄2gr. Apothecaries’ Liquid Measures. 60 minims (m) 8 fluid drams (fƷ ) 16 fluid ounces (f℥ ) 2 pints (O) 4 quarts (qt) = = = = = 1 fluid dram (fƷ ) 1 fluid ounce (f℥ ) 1 pint (pt or O) 1 quart (qt) 1 gallon (gal or C) Apothecaries’ Weight Measures 20 grains 3 scruples 8 drams (Ʒ) 12 ounces (℥) 1 pound (lb) = = = = = 1 scruple (℈) 1 dram (Ʒ) 1 ounce (℥) 1 pound (lb) 5760 grains (gr) APOTHECARIES’ SYSTEM Example 1: If a prescription calls for gr ii thyroid desiccated tablets and the pharmacist has gr ss tablets in stock, how many tablets of gr ss should be provided? gr ii = 2 grains gr ss = ½ grain 2 ÷ ½ = 4 tablets of gr ss answer: 4 tablets of gr ss APOTHECARIES’ SYSTEM Example 2: How many doses of fƷiv are present in O iiss of MaaloxR? O iiss = 2 ½ pints = 2.5 × 16 ounces = 40 ounces = 40 × 8 = 320 fluidrams = 320/4 = 80 doses answer: 80 doses THE AVOIRDUPOIS SYSTEM 1 ounce (oz) 1 pound (lb) = 437.5 grains = 7000 grains Practice problems 1. 2. 3. 4. Reduce 1.23 kg to grams Reduce 85 micrometers to centimeters A capsule contains the following amounts of medicinal substance: 0.075 g, 20 mg, 0.0005 g, and 500 µg. What is the total weight of the substances in the capsule. Multiply 820 mL by 12.5 and express the result in liters. Practice problems 5. 6. 7. 8. If an injectable solution contains 25 µg of a drug substance in each 0.5 mL. How many mL will be required to provide a patient with 0.25 mg of the drug substance. Convert 2 ½ pt to C Convert 2.5 qt to f℥ How many f℥ii-bottles of cough syrup can be optained from 5 gallons of the cough syrup? Practice problems 9. 10. 11. 12. Aspirin tablets contain 325 mg of aspirin. How may be prepared from 5 kg of aspirin? How many 15-minim doses can be obtained from a mixture containing f℥iii of one ingredient and fƷii of another? A formula contains ℈ii of ingredient A, Ʒi of ingredient B, Ʒiv of ingredient C, and gr viiss of ingredient D. calculate the total wieght of the ingredients. If a drug costs 8SR per oz (avoir), what is the cost of Ʒii? Home work 1. 2. 3. A vitamin capsule contains 6.25 µg of vitamin B12. how many capsules can be prepared from 1 g of vitamin B12. Convert 6.2 g to ng. A pharmacist had 1 gallon of phenobarbital elixir. At different time he dispensed Oi, f℥vi, fƷiv, Oss, f℥iss and f℥xii. What volume in fluidounces, of the elixir was left?