Pharmacy Concentration Calculations

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Questions and Answers

What does a 10% w/v solution represent?

10 g of drug in every 100 mL of product (correct)

10 mL of drug in every 100 mL of product

10 g of drug in every 100 g of product

10 mL of drug in every 100 g of product

Which expression is used for a solid ingredient in a liquid vehicle?

% w/w

% v/w

% v/v

% w/v (correct)

What is the main consideration when determining the basis of calculation for a pharmaceutical preparation?

The nature of the ingredients (correct)

The volume of the product

The cost of the ingredients

The total number of parts

If a liquid component is mixed with a solid preparation, what calculation basis would be typically used?

Weight-in-weight Signup and view all the answers

How would you convert a 20% w/w solution to ratio strength?

1:5 Signup and view all the answers

Which concentration expression is used when both the drug and vehicle are liquids?

% v/v Signup and view all the answers

What does a 15% w/w solution imply?

15 g of drug in 100 g of product Signup and view all the answers

In what scenario would you typically use a weight-in-volume basis for calculations?

Powdered substance dissolved in a liquid Signup and view all the answers

When converting between percent strength and ratio strength, what is an important factor to keep in mind?

The total weight of the mixture Signup and view all the answers

What is the correct method to express a concentration for both drug and vehicle that are liquids?

% v/v Signup and view all the answers

What is ratio strength primarily used to express?

The concentration of active drug relative to the whole Signup and view all the answers

Which of the following correctly describes percentage weight-in-volume (w/v)?

Grams of drug per 100 mL of solution Signup and view all the answers

If a pharmacist prepares 4000 mL of a 5% dextrose solution, how many grams of dextrose are required?

400 g Signup and view all the answers

What does a 3% solution of ephedrine sulfate indicate in terms of grams per 100 mL?

3 g per 100 mL Signup and view all the answers

How do you convert a ratio of 1:4000 to percentage strength?

0.0025% Signup and view all the answers

What is the percentage strength (w/w) of a solution containing 75 g of a drug in 1500 g of solution?

5% Signup and view all the answers

To create a 20% w/w solution with a specific gravity of 1.15, how many grams of a drug are needed for 120 mL?

23.0 g Signup and view all the answers

What does a 10% v/v solution of peppermint oil indicate?

10 mL of oil in 100 mL of solution Signup and view all the answers

If peppermint spirit contains 10% v/v of peppermint oil, how much of the spirit contains 75 mL of peppermint oil?

1000 mL Signup and view all the answers

Study Notes

Concentration Expressions

Concentration is the ratio of the amount of an ingredient to the amount of product.
Concentration is measured in various ways.
In a solid ingredient in a liquid vehicle, the ratio is expressed as weight-in-volume (w/v).
If the liquid ingredient is in a solid vehicle, the ratio is expressed as volume-in-weight (v/w).
When both the drug and vehicle are liquids, the ratio is expressed as volume-in-volume (v/v).
If both the drug and vehicle are solids, the ratio is expressed as weight-in-weight (w/w).

Percentage Strength

Percentage describes the number of parts of the active drug relative to 100 parts of the total.
% w/w: grams of active drug per 100 grams of product.
% w/v: grams of active drug per 100 mL of product.
% v/v: milliliters of active drug per 100 mL of product.
Example: 10% w/v = 10 grams of drug in every 100 mL of total.

Special Considerations in Percentage Calculations

The nature of the ingredients in the pharmaceutical preparation dictates the basis of the calculation.
A powdered substance dissolved or suspended in a liquid vehicle is calculated on a weight-in-volume (w/v) basis.
A powdered substance mixed with a solid or semisolid (e.g., ointment base) is calculated on a weight-in-weight (w/w) basis.
A liquid component in a liquid preparation is calculated on a volume-in-volume (v/v) basis.
Weight may need conversion to liquid or vice versa (e.g., grams to milliliters).

Ratio Strength

Ratio strength is another method of expressing drug concentration.
It's expressed in terms of parts of active drug related to any number of parts of the entire product.
Ratio strength is expressed as a ratio, unlike percentage, which is calculated relative to 100 parts.
Example: A 1:1000 ratio strength indicates one part of active drug to 1000 parts of the product.

Interconversion of Percentage and Ratio Strength

Percentage concentration to ratio strength: Convert to the correct units (e.g., grams to milligrams), set the denominator of the ratio proportion equation to 100 and adjust the numerator based on the original concentration
Ratio strength to percentage strength: Set the numerator to 1, and adjust denominator to 100. Calculate and adjust accordingly.

Other Concentration Expressions

Milligram per Milliliter (mg/mL): Expresses concentration as milligrams of solute per milliliter of solution.
Parts per Million (ppm): Represents the parts of a substance per one million parts of the whole.
4 ppm = 4 parts per 1,000,000
Conversion examples provided for calculating mg/mL from Percentage and ratio strength.

Examples of Calculations

Include numerous examples to demonstrate calculations for different types of concentration expressions (v/v, w/v, w/w, mg/mL ppm, ratios).
Show steps for problem-solving using percentages, ratios, and conversions.

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Description

This quiz focuses on understanding concentration expressions and percentage strength calculations in pharmacy. It covers various ways to express ratios of ingredients and special considerations in percentage calculations. Test your knowledge on weight-in-volume, volume-in-weight, and other measurement techniques.