19 Concentrations and Dilutions

State Standard 22) Calculate correct doses required when given a simulated prescription for a pediatric dose, adult dose, and geriatric dose based on weight (if applicable), length of administration, times per day of administration, and presence of other diseases/disorders.**

Objectives Students will be able to… Determine correct dosage calculations using concentrations and dilutions.

Concentrations and Dilutions Concentrations of many pharmaceutical preparations are expressed as a percent strength. Percent strength represents how many grams of active ingredient are in 100 mL. Percent strength can be reduced to a fraction or to a decimal, which may be useful in solving these calculations.

Concentrations Weight/Weight Concentrations When a solid active ingredient (e.g., a powder) is mixed with a solid base (e.g., an ointment)

Concentrations Weight/Weight Concentrations Steps Set up a proportion with the amount of active ingredient listed over the total quantity, as grams over grams. Convert the proportion to a decimal (by dividing the numerator by the denominator).

Concentrations Weight/Weight Concentrations Steps Multiply the converted number by 100 to express the final concentration as a percentage.

Concentrations Weight/Weight Concentrations Practice 12 g of active ingredient powder is in a 120 g compounded cream. What is the concentration? 30 g of a compounded ointment contains 105 mg of neomycin sulfate. What is the final concentration?

Concentrations Weight/Weight Concentrations Practice Bactroban® ointment contains 0.6 g of mupirocin per 30 g tube. What is the percent strength?

Concentrations Weight/Volume Concentrations When a solid active ingredient (e.g., a powder) is mixed with a liquid base (e.g., a syrup) Steps Set up a proportion with the amount of active ingredient listed over the total quantity, as grams over milliliters.

Concentrations Weight/Volume Concentrations Steps Convert the proportion to a decimal (by dividing the numerator by the denominator). Multiply the converted number by 100 to express the final concentration as a percentage.

Concentrations Weight/Volume Concentrations Practice 25 g of active ingredient powder is mixed with 250 mL of distilled water. What is the final percent strength? 30 mL of Xylocaine® liquid contains 1.5 g of lidocaine HCl. What is the final concentration?

Concentrations Weight/Volume Concentrations Practice Cleocin T® contains 10 mg of clindamycin phosphate per mL of solution. What percent strength is this product?

Concentrations Volume/Volume Concentrations When a liquid active ingredient is mixed with a liquid base (e.g., an emulsion). Steps Set up a proportion with the amount of active ingredient listed over the total quantity, as milliliters over milliliters.

Concentrations Volume/Volume Concentrations Steps Convert the proportion to a decimal (by dividing the numerator by the denominator). Multiply the converted number by 100 to express the final concentration as a percentage.

Concentrations Volume/Volume Concentrations Practice 10 mL of active ingredient is mixed with distilled water to total 200 mL. What is the final concentration? 180 mL of active ingredient is added to 820 mL of an alcohol-based solution. What is the final strength?

Concentrations Volume/Volume Concentrations Practice 150 mL of active ingredient is combined with 350 mL of normal saline. What is the final strength?

Dilutions Stock solutions are strong (very concentrated) solutions that can be diluted to a desired strength. Larger volume mixed with stock solution is called the diluent.

Dilutions Stock solutions Formula used to calculate dilutions Q1 × C1 = Q2 × C2 Q represents the quantity expressed in milliliters or grams. C represents the concentration listed as a percent strength. Q1 represents the initial quantity or volume.

Dilutions Stock solutions Formula used to calculate dilutions Q1 × C1 = Q2 × C2 Q2 represents the final, or desired, quantity or volume. C1 represents the initial concentration expressed as a percentage (stock solution). C2 represents the final, or desired, concentration expressed as a percentage (final solution).

Dilutions Stock solutions Practice How much stock solution of hydrogen peroxide 12% solution will you need to make 480 mL of hydrogen peroxide 3% solution? Q1 = X C1 = 12% Q2 = 480 mL C2 = 3%

Dilutions Stock solutions Practice You had 60 g of a 20% coal tar solution, which you diluted to produce 100 g. What is the strength of the final product? Q1 = 60 g C1 = 20% Q2 = 100 g C2 = X

Summary Concentrations and dilutions are just a series of simple ratios and proportions. Concentrations and dilutions are important in a variety of pharmacy settings.

Activity Complete drug cards for the following… Lisdexamfetamine (Vyvanse) Niacin (Niaspan) Naproxen (Aleve) Complete the Dilutions Calculations Activity on the class website.