SBP3301 FARMAKOLOGI

SYSTEM OF WEIGHTS AND MEASURES

1. THE METRIC SYSTEM

This system is being accepted as the international standard. The basis of the metric system is an arbitrary unit of the linear measure, the meter, from which other units of the system were derived:

The liter: 1,000 cubic centimeters is the cube of one tenth of a meter, and is the unit of volume

The gramme: is the unit of weight, and is the weight of a cubic centimeter of water at 40 C.

1.1 Weights (Mass)

1 kilogram (kg.) = 1,000 grammes1 gramme (G) = 1,000 milligrams. The official abbreviation is “g”, but in

prescription writing the symbol “G” should be used to avoid possible confusion with “gr” (grain)

1 milligram (mg) = 1,000 micrograms (mcg). The official abbreviation is “ug”, but in prescription writing the symbol “mcg” should be used to avoid possible confusion with “mg” (milligram)

1.2 Measures (fluid volume)

1 liter (l) = 1,000 milliliters (ml)

1.3 Length

1 Meter (m) = 100 centimeters (cm)= 1,000 millimeters (mm)

1 Millimeter = 1,000 microns (u)1 Micron = 1,000 millimicrons (mu)

2. THE IMPERIAL SYSTEM

This system is complicated by being divided into two separate systems with some units of common name but different value, particularly with respect to units of weight. The older “Apothecaries System” is still used in some places for pharmaceutical measures and prescription writing, while the “Avoirdupois System” is used for commercial transactions.

2.1 Weights

Both Apothecaries and Avoirdupois Systems have in common the grain (gr) which is different values and different symbols.

2.1.1 Apothecaries weight

20 grains (gr) = 1 scruple ()3 scruples = 1 drachm () = 60 grains8 drachms = 1 ounce ( ) = 480 grains12 ounces = 1 pound (lb) = 5760 grains

Note: in prescription writing the weight denomination is expressed by the symbol followed by the number in Roman numerals. These number have a line drawn above them and above this is a dot is placed above each unit numeral. One half may be abbreviated “__”. Other fractional quantities are written normally.

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2.1.2 Avoirdupois weight

1 pound (lb) = 7,000 grains= 16 ounces

1ounces (oz) = 437.5 grains (gr)

Notes :1. Avoirdupois weights should be written in Arabic numerals followed by the unit symbol2. The Apothecaries’ ounce (480 grains) is heavier than the Avoirdupois ounce (437.5 grains).

Conversely the Avoirdupois pound (7,000 grains) is heavier than the Apothecaries’ pound.

2.2 Fluid Measures

Here both the Apothecaries’ and Avoirdupois Systems have the identical values, although different symbols are again used. The rules for the choice of numerals and positioning of symbols are the same as for the weight of the corresponding system.

Apothecaries’ symbol Avoirdupois symbol1 minim* 1 m

* 1 minim is approximately equal to one drop of water

Apothecaries’ symbol Avoirdupois symbol60 minims = 1 fluid drachm 1 fl. dr.8 fluid drachm = 1 fluid ounce 1 fl. oz.20 fluid ounces = 1 pint 1 pt2 pints = 1 quart 1 qt8 pints = 1 gallon 1 gal.

3.0 Approximate Imperial-Metric Equivalents

3.1 Weight

1 grain = 65 mg 100 mg = 16.9 m1 ounce (Avdp.) = 28 G 1 G = 15.4 gr.1 ounce (Apoth.) = 31 G 1 kg = 2.2 lb1 pound (Avdp.) = 454 G

3.2 Measures3

60 minims = 3,5 ml. 1 ml = 16.9 m1 fl.oz = 28.4 ml. 1 l = 35 fl. oz

= 1.8 pt= 0.22 gal

1 pt = 568 ml.1 gal. = 4.5 l

3.3 Household Measures

A drop = 1 minim = 0.06 mlA teaspoonful = 60 minims = 3.5 mlA dessertspoonful = 120 minims = 7 mlA tablespoonful = ½ fl. oz. = 14 mlA cupful = 8 fl. oz = 227 ml

Note: The American Standard pint contains only 16 fluid ounces. Accordingly American pints, quarts and gallon are four-fifths of the corresponding standard Imperial measure.

4.0 Calculation of drug dosage

Although there are examples to the contrary, recommended drug dosage is most commonly expressed as units of drug weight per unit of animal body weight. Units of drug weight most commonly used are micrograms (ug), milligram (mg), grams (gm) and grains (gr). Units of body weight most commonly used are kilograms (kg) and pounds (lb).

Commercial drug preparations include tablets, boluses and solutions or suspensions, drug concentration will appeared on the drug label. In the case of solutions or suspensions, drug will be expressed in one of the following ways:

4.1 Units weights per unit volume:

eg: 10 mg/ml25 gm/l3 gr/oz

4.2 Dilution (weight in gm : volume in ml)

e.g: 1:1000 (this is equal to 1 gm/l, 1 mg/ml, or 1 x 10 -3 gm/ml)1: 50,000 (this is equal to 1 gm/50 l, 0.02 gm/l, 0.02 mg/ml or 2 x 10 -5 gm/ml)1:1,000,000 (this is equal to 1 gm/1000 l, 1 mg/l, 1 ug/ml or 1 x 10 -6 gm/ml)

4.3 Percent: (weight in gm) x 100(volume in ml)

e.g: 100 % solution contains 1000 mg/ml10 % solution contains 100 mg/ml1 % solution contains 10 mg/ml0.1 % solution contains 1 mg/ml0.01 % solution contains 0.1 mg/ml0.001% solution contains 0.01 mg/ml

Notes: Do not confuse this expression of drug concentration as percent solution with the common clinical chemistry usage of mg % (mg/100 ml) to express concentration of a substance in body fluids. Drug concentrations in commercial drug preparations are almost never expressed as mg %.

In calculation drug dosage, you will often be faced with situation like the following example:

Recommended dosage of drug X : 22 mg/kg body weightConcentration of drug solution : 100 mg/mlWeight of animal: 50 lb

The simplest way to accomplish the necessary calculation (and that can often be done “in your head”) is to transform either the body weight units or the drug dose units ( e.g. 22 mg/kg equals to 10 mg/lb) and then to calculate the volume of solution per unit body weight that must be administered (e.g. for a dose of 10 mg/lb, one would need 0.1 ml of the 100 mg/ml solution per pound). Thus, for a 50 lb animal, the dose would be 5.0 ml.

Many therapeutic misadventures are due to goofs, in calculating drug dosage. Since both the therapeutic range and the margin of safety are quite narrow for many drugs, accurate calculation of drug dosage can often mean success and disaster. You will be asked to make calculations of drug dosage both in laboratory and examinations in this course.

Sample Problems in Dosage Calculation

1. A local anesthetic solution is labeled “1.5 % procaine HCL and 1: 50,000 epinephrine HCl”. What is the concentration of each drug in mg/ml?

2. You have 1 fl oz of antiseptic solution labeled “0.1 % active ingredient”. In order to flush a wound with this drug at a concentration of 1: 10,000, how much water would you add to the 1 fl oz antiseptic solution?

3. You wish to administer a sulfonamide solution intravenously to a 45 kg sheep. The recommended dose is 200 mg/kg and the solution is labeled 33.3 % w/v. What volume should be administered?

4. Some commercial drugs preparations of Na pentobarbital anesthetic are labeled “one grain per cc. Administer at dose of 1 cc per 5 lb body weight.” What is the dose in mg/kg?

5. You are testing the effect of a drug on the blood pressure in 4 rats with the following body weight: 250, 240, 245, 265 g. Recommended dosage is 50 mg/kg.

a. Calculate the total amount of drug required for the testb. If the drug is in form of solution (28 mg/ml) calculate the amount in ml required for each rat.

6. You are preparing 1 L of 0.25M Sodium Chloride. How much sodium chloride is needed?(Atomic weight Na = 23, Cl = 35.5)

7. You have 100 mL stock solution of 0.25M sodium chloride. How do you prepare a 150 mM working solution?

a. Prepare the working solution from all the stock solution.b. Prepare 10 ml of working solution with the concentration of 150mM.

8. Stock solution of adrenalin is 1:1000. Prepare a working solution of 0.5 mg/mL.