Table of Contents
Alligation Alternate is a valuable method used in hospital pharmacies to prepare accurate drug dosages by mixing different concentrations of solutions. It helps pharmacists achieve the desired strength efficiently and safely, especially when commercial formulations are unavailable or impractical.
Understanding Alligation Alternate
Alligation Alternate is a technique that involves calculating the quantities of two solutions with different strengths to obtain a solution of a desired strength. It is particularly useful in compounding medications where precise concentrations are essential for patient safety.
Case Study 1: Preparing a 10% Dextrose Solution
A hospital pharmacy needs to prepare 500 mL of a 10% dextrose solution. The available stock solutions are 5% and 20%. Using alligation alternate, the pharmacist calculates the required volumes of each stock solution.
- Desired concentration (Cdesired): 10%
- Concentration of weaker solution (Cweak): 5%
- Concentration of stronger solution (Cstrong): 20%
- Total volume (V): 500 mL
Difference between Cstrong and Cdesired: 20% – 10% = 10
Difference between Cdesired and Cweak: 10% – 5% = 5
Ratio of volumes:
Weak solution: 10 (from Cstrong difference)
Strong solution: 5 (from Cweak difference)
Total parts: 10 + 5 = 15
Volume of weak solution: (10/15) × 500 mL = 333.33 mL
Volume of strong solution: (5/15) × 500 mL = 166.67 mL
The pharmacist mixes 333.33 mL of 5% dextrose with 166.67 mL of 20% dextrose to obtain 500 mL of 10% dextrose solution.
Case Study 2: Preparing a 15% Sodium Chloride Solution
In another scenario, a hospital requires 250 mL of a 15% sodium chloride solution. The available solutions are 10% and 20%. The pharmacist applies alligation alternate to determine the appropriate volumes.
- Desired concentration: 15%
- Weak solution: 10%
- Strong solution: 20%
- Total volume: 250 mL
Difference between Cstrong and Cdesired: 20% – 15% = 5
Difference between Cdesired and Cweak: 15% – 10% = 5
Volumes ratio:
Weak solution: 5
Strong solution: 5
Total parts: 10
Volume of each solution:
Weak solution: (5/10) × 250 mL = 125 mL
Strong solution: (5/10) × 250 mL = 125 mL
The pharmacist mixes 125 mL of 10% sodium chloride with 125 mL of 20% sodium chloride to prepare 250 mL of 15% solution.
Benefits of Using Alligation Alternate in Hospital Pharmacies
Implementing alligation alternate offers several advantages:
- Ensures precise drug concentrations
- Reduces medication errors
- Optimizes resource utilization
- Saves time in compounding medications
- Enhances patient safety
Conclusion
Alligation alternate is a fundamental skill for hospital pharmacists, enabling them to prepare accurate and safe medication solutions efficiently. Mastery of this technique improves pharmacy practice and patient care outcomes.