Alligation in Pharmaceutical Calculations
- S-1-Pharmaceutics I
- Feb 27
- 1 min read
Updated: Mar 2
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Alligation in Pharmaceutical Calculations is a method used in pharmacy for mixing solutions or components of different concentrations to achieve a desired concentration.
It’s useful in compounding and preparing pharmaceutical mixtures.
Alligation Medial
This method calculates the average strength of a mixture based on the quantities and concentrations of the individual solutions.
Formula
Where:
C1,C2,… = concentrations of the solutions.
Q1,Q2,… = quantities of the solutions.
Alligation Alternate
This method is used to mix two solutions of known concentrations to achieve a desired concentration.
Steps
Place the stronger and weaker concentrations on opposite sides of a grid.
Write the desired concentration in the middle.
Subtract the desired concentration from both the stronger and weaker concentrations (ignoring negative signs) to determine the parts of each solution.
Example
To make 500 mL of a 10% solution using 15% and 5% solutions:
15 – 10 = 5 and 10 – 5 = 5
This means equal parts of the two solutions should be mixed.
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