Alligation Method in Pharmaceutics

Alligation, Pharmaceutics, Pharmacy, Notes, Metrology
  • In Alligation method, two different strength solutions containing the same active ingredient can be combined to achieve the desired strength.
  • This method may be used for both weight or volume.
  • Alligation method is used to calculate the amount of high-strength product and a low-strength product that must be added together to make an intermediate-strength product.

How to use Alligation method

Alligation method, Pharmacy
Alligation method
  1. In the upper left corner, place the given highest concentration as a whole number. In the lower left corner, write the given lowest concentration. In the center of the box, write the desired concentration.
  2. Write the difference between the upper left corner and the centre corner in the lower right corner (subtracting the smaller number from the larger number). Next, write the difference between the lower left corner number and the centre number in the upper right corner. The numbers on the right corners represent the required part of each solution to make a new solution.
  3. Add the numbers in the right sides to determine the total part needed for the new solution

Example 01 :- How to prepare a 500 mL of 30% v/v alcohol from a 70 % v/v alcohol solution and 20 % v/v alcohol solution?


Desired= 30% v/v alcohol

Given= 70 % v/v alcohol solution and 20 % v/v alcohol solution

Step 1: Write the given/known strength quantities and desired strength

Step 2: Subtract (Diagonal) & write the difference in the corner as mentioned in procedure

Alligation method, Pharmaceutical, Calculation, Pharmapedia,Pharmacy,
Alligation method

Example 02: How to prepare a 1000 mL of 50% v/v alcohol from a 60 % v/v , 40 % v/v & 10% v/v alcohol solution ?


Desired= 50% v/v alcohol

Given= 60 % v/v , 40 % v/v & 10 % v/v alcohol solution.

Follow as above steps as per example 01.

Alligation method, Pharmaceutical, Calculation, Pharmapedia,Pharmacy,
Alligation method with example

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