Conducting Physical Stability Studies on Emulsions
1) Purpose
The purpose of this SOP is to describe the process for conducting physical stability studies on emulsions. Physical stability is essential to ensure that emulsions maintain their homogeneity, droplet size distribution, and absence of phase separation over time under various storage conditions. This helps establish the shelf life and suitability of emulsions for commercial or clinical use.
2) Scope
This SOP applies to personnel involved in the formulation, testing, and quality control of emulsion-based products. It covers the preparation, evaluation, and testing of emulsions to monitor droplet size distribution, zeta potential, viscosity, and visual signs of instability such as creaming, coalescence, or phase separation.
3) Responsibilities
- Formulation Scientists: Responsible for preparing emulsions for stability testing and ensuring all necessary documentation is completed.
- QC Team: Responsible for conducting physical stability tests, including droplet size analysis and visual inspection, and documenting results.
- QA Team: Responsible for reviewing stability study results and ensuring compliance with regulatory guidelines and good manufacturing practices (GMP).
4) Procedure
4.1 Preparation for Stability Testing
- 4.1.1 Prepare sufficient quantities of the emulsion for stability testing and ensure uniformity across all test samples.
- 4.1.2 Store the emulsions in sterile, sealed containers, labeled with batch number, preparation date,
and storage conditions.
4.1.3 Divide the samples into groups for different storage conditions, such as refrigerated (4°C), room temperature (25°C), and accelerated conditions (40°C), as required by the protocol.
4.2 Key Parameters for Physical Stability
The following parameters must be monitored during physical stability studies:
- 4.2.1 Droplet Size Distribution: Use dynamic light scattering (DLS) or laser diffraction techniques to measure droplet size distribution. Track any significant changes in droplet size over time.
- 4.2.2 Zeta Potential: Measure the zeta potential to assess the colloidal stability of the emulsion. A high absolute zeta potential typically indicates better physical stability.
- 4.2.3 Viscosity: Measure the viscosity of the emulsion at regular intervals using a viscometer. Changes in viscosity may indicate instability or phase separation.
- 4.2.4 Visual Inspection: Regularly inspect the emulsion for signs of instability, including creaming, sedimentation, phase separation, or coalescence.
4.3 Sampling and Testing Time Points
- 4.3.1 Initial Tests: Conduct an initial assessment of the emulsion immediately after preparation, including droplet size analysis, zeta potential, and visual inspection.
- 4.3.2 Interim Tests: Perform stability tests at regular intervals (e.g., 1 month, 3 months, 6 months) for emulsions stored at different conditions.
- 4.3.3 Final Test: Conduct the final assessment at the end of the stability study period (e.g., 12 months).
4.4 Data Recording and Analysis
- 4.4.1 Record all test results in the Stability Test Report (see Annexure 1 for the template).
- 4.4.2 Analyze the data to identify any trends in physical stability, such as droplet size increase, zeta potential reduction, or viscosity changes.
- 4.4.3 Compare stability under different storage conditions to determine the optimal storage environment for the emulsion.
4.5 Stability Criteria
The emulsion is considered physically stable if it meets the following criteria throughout the stability study:
- 4.5.1 Droplet size remains within the acceptable range (as defined by the formulation protocol) with no significant increase.
- 4.5.2 Zeta potential remains within the range that indicates good colloidal stability (typically ±30 mV or higher).
- 4.5.3 No significant changes in viscosity or signs of creaming, sedimentation, or phase separation.
5) Abbreviations, if any
- DLS: Dynamic Light Scattering
- QC: Quality Control
- QA: Quality Assurance
6) Documents, if any
- Batch Manufacturing Record (BMR)
- Stability Test Report
- Droplet Size Analysis Report
- Zeta Potential Report
- Viscosity Measurement Report
7) References, if any
- ICH Q1A: Stability Testing of New Drug Substances and Products
- FDA Guidelines for Stability Testing of Emulsion Drug Products
8) SOP Version
Version 1.0
Annexure
Annexure 1: Stability Test Report Template
| Time Point | Storage Condition | Droplet Size (nm) | Zeta Potential (mV) | Viscosity (cP) | Visual Inspection | Operator Initials |
|---|---|---|---|---|---|---|
| Initial | 4°C | 100-200 nm | -30 to -50 mV | 10 cP | No creaming | Operator Name |
| 1 Month | 25°C | 100-200 nm | -30 to -50 mV | 10 cP | No creaming | Operator Name |
| 3 Months | 40°C | 100-200 nm | -30 to -50 mV | 10 cP | No creaming | Operator Name |