behavior.

2. Scope

This SOP applies to Analytical Method Development (AMD) personnel responsible for evaluating the flow behavior and structural integrity of topical products during formulation development, process optimization, and stability studies.

3. Responsibilities

• Analytical Scientist: Performs rheological testing, interprets flow curves, and documents results.
• QC Analyst: Assists in instrument setup, calibration checks, and sample handling.
• QA Executive: Reviews rheological data and approves final test reports for regulatory submissions.

4. Accountability

The Head of Analytical Method Development is accountable for method validation, equipment qualification, and ensuring that rheological assessments support product consistency and performance.

5. Procedure

5.1 Instrument and Materials

1. Rotational Rheometer (e.g., Anton Paar, TA Instruments)
2. Measuring geometries: cone-plate, parallel plate, or coaxial cylinder
3. Temperature control unit (25 ± 0.5°C standard)
4. Standard calibration oils (optional)

5.2 Sample Preparation

1. Equilibrate the topical formulation to room temperature (25°C).
2. Ensure the sample is homogeneous and free from air bubbles.
3. Load the sample gently into the measuring system to avoid altering its structure.

5.3 Instrument Setup

1. Select geometry based on sample type and consistency (e.g., cone-plate for creams, parallel plate for gels).
2. Set the measuring gap and temperature to test conditions (typically 25°C).
3. Trim excess sample using a spatula or edge tool.

5.4 Rheological Measurements

5.4.1 Flow Curve (Shear Stress vs. Shear Rate)

1. Program shear rate sweep from 0.1 to 100 s^-1.
2. Record corresponding viscosity values at each point.
3. Plot viscosity vs. shear rate to observe flow behavior (e.g., Newtonian, pseudoplastic).

5.4.2 Thixotropy

1. Apply an up-and-down shear ramp (increasing and then decreasing shear rate).
2. Record hysteresis area to assess structure recovery.

5.4.3 Oscillatory Testing (Viscoelastic Properties)

1. Perform amplitude sweep to determine linear viscoelastic region (LVER).
2. Conduct frequency sweep (0.1–10 Hz) at constant stress within LVER.
3. Record storage modulus (G’) and loss modulus (G”) to characterize gel strength.

5.5 Data Analysis and Reporting

1. Document flow behavior (e.g., shear thinning, thixotropic, viscoelastic).
2. Compare parameters across batches, time points, and formulations.
3. Highlight deviations or formulation instability if observed.

5.6 Validation Parameters

1. Repeatability: RSD of duplicate runs ≤ 5%
2. Ruggedness: Analyst-to-analyst and day-to-day variations ≤ 10%

6. Abbreviations

• G′: Storage Modulus
• G″: Loss Modulus
• LVER: Linear Viscoelastic Region
• QA: Quality Assurance

7. Documents

1. Rheological Profile Log – Annexure-1
2. Instrument Calibration Report – Annexure-2
3. Rheology Validation Summary – Annexure-3

8. References

• USP <1911>: Rheological Properties
• ICH Q6A: Specifications for New Drug Products
• FDA Guidance: Semisolid Drug Products – Quality Considerations

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name	Dr. Asha Tiwari	Rahul Sethi	Sunita Reddy
Designation	Rheology Scientist	QA Reviewer	Head – AMD
Department	Analytical Method Development	QA	Analytical Method Development

11. Annexures

Annexure-1: Rheological Profile Log

Sample ID	Shear Rate Range	Viscosity Profile	G′ (Pa)	G″ (Pa)	Status
TP-257-01	0.1–100 s⁻¹	Shear thinning	120	45	Pass

Annexure-2: Instrument Calibration Report

Date	Instrument ID	Calibration Fluid	Expected Value (cP)	Observed	Status
21/05/2025	RH-03	1000 cP	998 cP	Pass

Annexure-3: Rheology Validation Summary

Rheological method validated for gel formulation G-257 with precision RSD ≤ 1.5%, excellent repeatability, and viscoelastic profiling across all time points. Suitable for formulation optimization and stability analysis.

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
21/05/2025	2.0	Included oscillatory testing and updated USP reference	Annual SOP Review	Sunita Reddy
15/03/2022	1.0	Initial SOP Release	New SOP	QA Head