Pharmaceutics 1 Lecture: Percentage Solutions and Conversions PDF

Pharmaceutics 1 Dr. Fatima Aloum PHARMACEUTICAL CALCULATIONS Weights & Measures: There are two systems of weights and measures: ▪ The Imperial System ▪ The Metric System The imperial system It is an old system of weights and measures. That includes inches, ounces, feet, pounds, cups, gallons...

Pharmaceutics 1 Dr. Fatima Aloum PHARMACEUTICAL CALCULATIONS Weights & Measures: There are two systems of weights and measures: ▪ The Imperial System ▪ The Metric System The imperial system It is an old system of weights and measures. That includes inches, ounces, feet, pounds, cups, gallons, miles, and tons MEASUREMENTS OF Weight: Weight is a measure of the gravitational force acting on a body and is directly proportional to its mass. The imperial systems are of two types: (a) Avoirdupois system (b) Apothecary system Avoirdupois system Avoirdupois is a measurement system of weights that uses pounds and ounces as units. In this system pound (lb) is taken as the standard of weight (mass). 1 pound avoir (lb) = 16 oz (ounce). 1 pound avoir (lb) = 7000 grains (gr) Apothecary or troy system The apothecary system, originated as the system of weights and measures for dispensing and prescribing medications In this system grain (gr) is taken as the standard of weight (mass). 1 pound apoth (lb) = 12 ounces 1 pound apoth (lb) = 5760 grains Measurements of volumes 1 gallon (c) = 4 quart 1 quart = 2 pint (o) 1 pint (o) = 20 fluid ounce 1 fluid ounce = 8 fluid drachm 1 fluid drachm = 3 fluid scruple 1 fluid scruple = 20 minims The Metric System Is system of measurement invented by the French in 1790. Also called the International system of units. It is the most used system of measurement on earth. Common Units: ▪ Length: Meter ▪ Volume: Liter ▪ Weight : Kilogram Measure of length 1meters(1m)= 100centimeter = 1000millimeters = 1000000 micrometers = 1000000000 nanometers Measure of volume 1liter (L) = 1000milliliters = 1000000microliters(μL) Measure of weight 1 gram (g) = 1000milligrams (mg) = 1000000 micrograms(μg) PERCENTAGE SOLUTIONS A percentage is the number of parts per 100. The concentration of a substance can be expressed in the following three types of percentages: Weight in volume (w/v): number of grams of active ingredient in 100 ml of liquid. Weight in weight (w/w): number of grams of active ingredient in 100 g of mixture. Volume in volume (v/v): the volume of active ingredient ml in 100 ml of liquid.  In each case, the concentration in percentage is calculated as the fraction of the volume or weight of the solute related to the total volume or weight of the solution. Weight in volume (w/v) Solute: 1part by weight Solvent : 100 parts by volume In this case the general formula for 1% (w/v) is: Solute: 1 g Solvent: up to 100 ml Example 1: Calculate the weight of potassium permanganate needed to prepare the following recipe: 0.02%(mg/mL) of potassium permanganate 250mL distilled water up to 0.02% Means 0.02 mg in 100ml x mg in 250ml X=(250x0.02)/100= 0.05mg Example 2 : How many milligram of neomycin in 50 ml of neomycin solution 1% mg/ml Every 100ml of the solution contain 1mg of neomycin 50 ml x mg X=(50x1)/100=0.5mg Weight in weight (w/w) Solute: 1part by weight Solvent : 100 parts by Weight In this case the general formula for 1%(w/w) is: Solute: 1 g Solvent: up to 100 g Example : 20 g of NaCl added to enough sand to make 200 g of mixture would result in a 10 % (w/w) NaCl/sand mixture. Weight in volume (v/v) Solute: 1part by volume Solvent : 100 parts by volume In this case the general formula for 1% (v/v) is: Solute: 1 ml Solvent: up to 100 ml Example : How many ml of liquid phenol should be used to prepare the following recipe: 2.5% of liquid phenol 240 ml calamine lotion 2.5 ml of liquid phenol in 100 ml X ml 240ml X = 2.5 X 240 / 100= 6ml Domestic Measure Metric System Imperial system 1 drop 0.06ml 1 minim 1 teaspoonful 5 ml 1 fluid drachm 1 desert spoonful 8 ml 2 fluid drachm 1 tablespoonful 15 ml 4 fluid drachms 1 wineglassful 60 ml 2 fluid ounces 1 teacupful 120 ml 4 fluid ounces 1 tumblerful 240ml 8 fluid ounces  1 kg = 2.2 pounds (lb) 1 ounce apoth = 30 g 1 pound avoir = 450 g 1 grain = 65 mg Example: A Prescription is received for a dose of 30 grains of a drug. How many grams is the dose? 1gr=65mg 30 gr=30x65=1950mg=2g Example: 5 fluid ounce of a liquid is requested. How many ml should be provided? 1 fl oz = 30 ml 5 fl oz = 5 X 30 = 1500 ml Example: A patient reports that she weights 12 stones 6 pounds. What is her weight in kg ? (1 stone = 14 lb) There are 14 pounds per stone Wt=(12X14) +6 = 174lb 1kg =2.2lb 174/2.2= 79.01kg Question 1: A patient is prescribed 0.25 mg of digoxin orally once daily. How many tablets should you give? (Stock = digoxin 250 microgram tablets) Question 2: If you want to administer 3 mg / kg of 1 % lidocaine to a 72 kg man, how many mLs should you give? Question 3: A patient is prescribed prednisolone 40 mg once daily in the morning for 5 days. a) How many tablets should you give the patient every morning? b) What is the total number of 5 mg tablets required to complete the course? (Stock = prednisolone 5 mg tablets