Chapter 13 • Interpret labels for the weight/volume of solute in solvent • Dilute stock medications to the required strength using strengths expressed as percentages, fractions, and ratios • Calculate the weight/volume of active ingredient in a substance • Using alligation, calculate the weight/volume of stock medications needed to prepare a desired compound Pretest Interpret the amount of epinephrine on the label in the metric system using ratio strength. ____________________ How many parts of alcohol are in the solution? ____________________ How many parts of solvent are in the solution? ____________________ What is the metric volume of Burrow’s solution in the total volume? ____________________ What is the volume of solvent in the mixture? ____________________ How many milliliters of sodium hypochlorite should be used to prepare the solution? ____________________ How many milliliters of solvent would be necessary? ____________________ If the physician changes the order to 130 mL of 1 : 15 sodium hypochlorite solution, how many milliliters of the solute would be needed? ____________________ Now, how many milliliters of solvent would be needed? ____________________ 10. An order is to supply 10 mL of a drug at 50 mg/mL. The stock supply is 2.5 g/10 mL. How many milliliters of stock supply would be necessary? ____________________ How many milliliters of diluent would be necessary? ____________________ 11. A physician asks that 500 mL of a 10% solution of a medication be prepared. The stock supply of the solution is 75%. Note this calculation is completed using a formula. How many milliliters of diluent would be necessary? ____________________ How many milliliters of the medication stock solution would be necessary? ____________________ How many tablet(s) would be necessary to prepare the solution? ____________________ How many milliliters of solution would be necessary? ____________________ How many milliliters of silver nitrate stock solution would be necessary to prepare the solution? ____________________ How many milliliters of solvent would be necessary? ____________________ How many milliliters of solute would be necessary? ____________________ How many milliliters of solvent would be necessary? ____________________ How many milliliters of solute would be needed for 500 mL of solution? ____________________ How many milliliters of solvent would be needed for 500 mL of solution? ____________________ How many grams of Neomycin would be added to fulfill the order? ____________________ How many tablets of Neomycin would be added to each liter of the product? ____________________ How many milliliters of epinephrine would be added to the fluids for injection? ____________________ How many milliliters of epinephrine would be needed to be added to 1000 mL to provide the ordered strength of medication shown above? ____________________ If the physician wanted the patient to receive epinephrine 3 mg in the 500 mL of D-5-W to follow the 1000 mL, how many milliliters of the medication would be added to the fluids for injection? ____________________ How many milliliters of calcium gluconate would be added to the fluids? ____________________ How many milliliters of IV fluids would be used? ____________________ How many milliliters of the 25% Lysol would be necessary to prepare the solution? ____________________ How many milliliters of solvent are needed for the solution? ____________________ How many milliliters of the 1 : 2 creosol solution should be obtained to prepare this order? ____________________ How many milliliters of solvent should be added for the order as above? ____________________ With percentage preparations, the easiest method for calculation is the ratio and proportion method. If a review of the ratio and proportion method is necessary, see Chapter 2. Example 13-1 What is the weight of hydrocortisone in the stock medication? ____________________ What is the weight of hydrocortisone in each 100 g of base to complete this order? ____________________ What weight of the 10% stock medication is needed to prepare the 2.5% cream? ____________________ How many grams of hydrocortisone would be needed to prepare 5 g of the 2.5% cream? ____________________ What is the weight of hydrocortisone in stock medication? The label interpretation of 10% is 10 g in 100 g of stock medication. The desired weight of hydrocortisone in the order is 2.5 grams. What weight of the 10% stock medication is needed to prepare the 2.5% cream? How many grams of hydrocortisone are needed to prepare 5 g of the 2.5% cream? Example 13-3 How many micrograms of the drug will be needed to prepare the order? x = 10 × 15 mcg or 150 mcg of the medication is necessary How many milliliters of the stock medication are necessary? How many milliliters of diluent are necessary? The following formula will allow the calculation of these solutions: Example 13-4 First interpret that 1% is 1 g/100 mL. If the medication available is lidocaine 5%, what volume of lidocaine is necessary for this order? To calculate volume of solvent in volume of solution, use the following: What is the amount of hand lotion that should be used to prepare this solution? When a volume of a known solution requires reducing or enlarging to meet a physician’s order, the original strength of the preparation may be used for the calculation of the new volume or weight of the preparation. For example, using the above calculations in Example 13-4, if the physician desires 100 mL, the answer can be figured using ratio and proportion. Practice Problems A Calculate the following problems. Round all answers to tenths. Show all your calculations. 1. How many grams of sucrose would be needed to make 1000 mL of 75% solution? ____________________ How many grams of sucrose would be needed for 250 mL of 75% solution? ____________________
Calculation of Mixtures from Stock Medications
1 A label for isopropyl alcohol reads 70% isopropyl alcohol.
2 A label reads Zephiran chloride 0.2%.
3 A label reads sodium hypochlorite 10%.
4 A label reads epinephrine 2.25% nebulizer.
5 The label on isopropyl alcohol reads 1 : 2.
6 The label on a 25 mL saline vial shows a 1 : 25 solution.
7 A Burrow’s solution 100-mL label reads 1 : 7.5.
8 A physician orders 1 L of a 10% boric acid solution to be used for compresses.
9 A physician orders 65 mL of a 1 : 15 sodium hypochlorite solution to be used in the office.
12 A physician asks that 325 mL of a 1% sodium bicarbonate solution be prepared. The stock medication is 650 mg/tab.
13 A physician asks the pharmacy to prepare 1 L of a 1 : 2000 silver nitrate solution to be used for an irrigation solution. The stock solution is 1% silver nitrate solution.
14 Prepare 250 mL of a 0.02% benzalkonium chloride solution to be used for cleansing skin before surgery. Stock strength of the solute is 1%.
15 A physician desires 3 L of a 15% Neomycin solution to use for irrigation of a wound. The available Neomycin is found in 0.5 g tablets.
16 A physician wants a patient to receive epinephrine 4 mg. The available medication is 1 : 1000 injectable. The medication is to be added to 500 mL of D-5-W.
17 A physician orders calcium gluconate 0.5 g to be used to prepare 1 L IV fluids. The medication is available in a vial marked calcium gluconate 1 : 2000 injectable.
18 A medical office needs 0.25 L of a 10% Lysol solution for disinfecting the office.
19 A physician desires 100 mL of a 50% creosol solution to be prepared from a 1 : 2 creosol solution.
20 A stock bottle of sodium perborate 1 : 50 solution is available. The dentist asks that 200 mL of solution be prepared.
Interpreting Solution Labels and Calculating Solutions In Percentages
Calculating Weight-in-Weight Solutions
Calculate Volume-in-Volume Solutions
Calculate the Amount of Drug and Solvent
Reducing and Enlarging Ordered Preparations
How many grams of sucrose must be dissolved in 500 mL of water to make a 75% solution? ____________________
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Calculation of Mixtures from Stock Medications
A physician asks that you prepare 100 grams of 2.5% hydrocortisone cream from available hydrocortisone cream 10%.
Tech Alert
How many milliliters of a 10% boric acid solution can be made from 20 g of boric acid?
A physician desires a 1% lidocaine preparation in hand lotion for itching. How many grams of lidocaine would be necessary to prepare 50 mL of this solution?