Alligation in Pharmaceutical Calculations

Alligation in Pharmaceutical Calculations is a method used in pharmacy to calculate the proportions of solutions of different strengths needed to achieve a desired concentration.
It’s useful in compounding and preparing pharmaceutical mixtures.

This method calculates the average strength of a mixture based on the quantities and concentrations of the individual solutions.
Formula:
$\text{Average Strength } (C) = \frac{(Q_{1} \times C_{1}) + (Q_{2} \times C_{2}) + \cdots}{Q_{1} + Q_{2} + \cdots}$
Where:
- C1,C2,… = concentrations of the solutions.
- Q1,Q2,… = quantities of the solutions.

This method is used to mix two solutions of known concentrations to achieve a desired concentration.
Steps:
1. Place the stronger and weaker concentrations on opposite sides of a grid.
2. Write the desired concentration in the middle.
3. 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
  - 15 – 10 = 5 and 10 – 5 = 5
- This means equal parts of the two solutions should be mixed.