Homework 9 altering product strength parts B & C key.pdf - Homework 9 – Altering product strength parts B C KEY 1 If a cough syrup contains in

Homework 9 altering product strength parts B & C...

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1 Homework 9 Altering product strength parts B & C - KEY 1. If a cough syrup contains in each teaspoonful, 1 mg of chlorpheniramine maleate and if a pharmacist desired to double the strength, how many milligrams of that ingredient would need to be added to a 60-mL container of the syrup? [Assume no increase in volume]. Answer: 12 mg Concentration of the syrup is 1 mg/5 mL Volume is 60 mL Amount of drug in syrup is 1 mg = W mg W = 12 mg 5 mL 60 mL To double the strength, we simply need to add 12 mg of chlorpheniramine maleate, answer . 2. A pharmacist mixed 80 g of a 5% w/w hydrocortisone cream with 120 g of a 7.5% (w/w) hydrocortisone cream. What is the percent strength (w/w) of hydrocortisone in the final product? Answer This practice problem is of the type of fortification and we can use mass balance. Since we do not have the percent strength of the final product, we cannot use alligation. Let’s write the information in the form of mass balance 80 g x 5% w/w + 120 g x 7.5% w/w = 200 g x j% w/w 80 g x 0.05 + 120 g x 0.075 = 200 g x j j = 4 g + 9 g = 0.065 200 g 0.065 x 100 = 6.5%, answer 3. A crude drug is required to contain 0.28% w/w of an alkaloid, the active compound. How many kilograms of a batch of crude drug containing 0.3% w/w alkaloid must be combined with 500 g of crude drug containing 0.20% w/w alkaloid in order that the resulting mixture will meet the required standard? Answer: 2 kg
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2 Let’s use mass balance [Since we know the final strength of the preparation we can also use alligation!] W g x 0.3% w/w + 500 g x 0.20% = ( W g + 500 g ) x 0.28% We will now change the percent strength to decimal fraction W g x 0.3 + 500 g x 0.2 = ( W g + 500 ) x 0.28 0.3 W g + 100 g = 0.28 W + g 140 0.02 W g = 40 W = 2000 g = 2 kg, answer 4. How many grams of pure hydrocortisone powder must be mixed with 45 g of 2% w/w hydrocortisone cream if one wishes to prepare a 5% w/w hydrocortisone cream? [Round to the nearest hundredth] Answer This practice problem can be solved by both mass balance and alligation method. Alligation method can be used when we know the strength of the final preparation, such as in this practice problem. Mass balance Q x 100% w/w + 45 g x 2% w/w = ( Q + 45 g ) x 5% w/w Expressing as decimal fraction 1 x Q + 0.02 x 45 g = (Q + 45 g) x 0.05 1 Q + 0.9 g = 0.05 Q + 2.25 g 0.95 Q = 1.35 g Q = 1.42 g, answer 5. How many grams of white petrolatum should be added to 12.5 g of a 10% w/w zinc oxide ointment in order to make a 2.5% w/w zinc oxide ointment? Answer: 37.5 g Since white petrolatum has 0% zinc oxide, it is a diluent and this practice problem of dilution can be solved using the QC equation
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3 Our unknown for the equation would be the final amount of 2.5% zinc oxide ointment 12.5 g x 10% w/w = W g x 2.5% w/w 12.5 x 10 g = W g x 2.5 g 100 g 100 g W g = 12.5 g x 10 g = 50 g 2.5 g Since this is the amount of the final 2.5% zinc oxide ointment, we still need to subtract the amount of the original 10% w/w zinc oxide ointment 50 g 12.5 g = 37.5 g petrolatum, answer 6. If a pharmacist adds 20 grams of pure sulfur to 80 grams of a 5% (w/w) sulfur ointment, what is the percent strength (w/w) of the final product?
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