at R&D and scale-up stages.

3. Responsibilities

• Formulation Scientist: Responsible for sample preparation and compatibility studies.
• Analytical Scientist: Conducts viscosity testing and documents results.
• QA: Verifies results and ensures compliance with guidelines.

4. Accountability

Head – Product Development and Head – QA are accountable for reviewing and approving the evaluation reports.

5. Procedure

5.1 Evaluation of Viscosity

1. Prepare samples at the final proposed drug concentration using compendial water or appropriate vehicle.
2. Measure viscosity using Brookfield viscometer, cone and plate viscometer, or capillary viscometer depending on formulation type.
3. Record viscosity in centipoise (cP) at specified shear rates and temperatures (typically 25°C ± 2°C).
4. Document data in the Viscosity Evaluation Form (Annexure-1).

5.2 Viscosity Acceptability Criteria

• IV formulations: < 10 cP
• IM or SC formulations: ≤ 50 cP (unless justified by clinical rationale)
• Must be suitable for injection through intended needle gauge.

5.3 Evaluation of Compatibility

1. Perform visual inspection under white and polarized light for precipitate formation, color change, or turbidity.
2. Conduct pH and osmolality checks immediately and after 24, 48, and 72 hours storage at 2–8°C and 25°C.
3. Perform container closure compatibility using vials, prefilled syringes, or ampoules with the final formulation.
4. Document all results in Compatibility Evaluation Sheet (Annexure-2).

5.4 Drug-Excipient Interaction Check

• Use FTIR, DSC, and HPLC impurity profile comparison between placebo and final formulation.
• Report any new peaks, degradation products, or pH drifts.

5.5 Stability Observation

1. Place samples under ICH stability conditions (e.g., 25°C/60% RH and 40°C/75% RH) for 7 days.
2. Monitor any changes in viscosity, pH, visual appearance, or compatibility during the study.

6. Abbreviations

• DSC: Differential Scanning Calorimetry
• FTIR: Fourier Transform Infrared Spectroscopy
• cP: Centipoise

7. Documents

1. Viscosity Evaluation Form – Annexure-1
2. Compatibility Evaluation Sheet – Annexure-2
3. Interaction Study Data Sheet – Annexure-3

8. References

• USP <912> – Injectability
• ICH Q6A – Specifications: Test Procedures and Acceptance Criteria
• FDA Guidance on Injectable Product Development

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation	Formulation Scientist	QA Executive	Head QA
Department	Product Development	Quality Assurance	Quality Assurance

11. Annexures

Annexure-1: Viscosity Evaluation Form

Sample Name	Shear Rate	Viscosity (cP)	Temperature	Comments
			25°C

Annexure-2: Compatibility Evaluation Sheet

Time Point	Condition	Appearance	pH	Osmolality	Conclusion
0 hr	25°C
24 hr	2–8°C

Annexure-3: Interaction Study Data Sheet

Includes overlay spectra, chromatograms, and degradation profile comparisons.

Revision History

Revision Date	Revision No.	Details	Reason	Approved By
01/07/2022	1.0	Initial SOP	Product development need	Head QA
18/06/2025	2.0	Added compatibility and interaction studies	Process refinement	Head QA