product safety, efficacy, and physical-chemical stability.

2. Scope

This SOP applies to the Analytical Method Development and Quality Control departments performing pre-formulation, formulation development, or routine compatibility testing between APIs and diluents such as normal saline, 5% dextrose, and Ringer’s lactate.

3. Responsibilities

• Analytical Scientist: Prepares compatibility samples and performs stability assessments.
• Formulation Scientist: Selects appropriate diluents based on clinical use and route of administration.
• QA Executive: Reviews results and ensures compliance with regulatory standards.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring proper design, execution, and documentation of API-diluent compatibility studies.

5. Procedure

5.1 Selection of Diluents

1. Choose diluents commonly used in clinical administration:
   • 0.9% Sodium Chloride Injection
   • 5% Dextrose Injection
   • Ringer’s Lactate
   • Sterile Water for Injection (WFI)

5.2 Sample Preparation

1. Reconstitute or dilute the API at intended concentration in selected diluent under aseptic conditions.
2. Prepare in duplicate for each time point and diluent.
3. Label and store at 2–8°C, 25°C, and 40°C for short-term observation (up to 48 hours) or as per stability protocol.

5.3 Parameters for Evaluation

1. Visual Inspection: Check for precipitation, color change, turbidity, or phase separation.
2. pH Measurement: Measure initial and final pH to detect instability.
3. Assay: Conduct potency test using validated HPLC/UV method.
4. Particulate Matter: Evaluate sub-visible particles using light obscuration or microscopic count.
5. Sterility (if required): Conduct test as per pharmacopoeial protocol (USP/Ph. Eur.).

5.4 Time Points for Analysis

• 0 hours (initial)
• 2 hours
• 4 hours
• 24 hours
• 48 hours

5.5 Acceptance Criteria

• No visible change in color, clarity, or formation of precipitate.
• Potency retained within 90%–110% of initial assay value.
• pH shift not exceeding ±0.5 units from baseline.
• Particulate matter within USP <788> limits.

5.6 Method Validation Parameters

1. Precision: RSD ≤ 2% for assay readings across time points.
2. Linearity: r² ≥ 0.999 over 80%–120% of nominal concentration.
3. Robustness: Ensure no significant variation under different diluent and storage conditions.

6. Abbreviations

• API: Active Pharmaceutical Ingredient
• RSD: Relative Standard Deviation
• WFI: Water for Injection
• QA: Quality Assurance

7. Documents

1. API-Diluent Compatibility Log – Annexure-1
2. HPLC Chromatogram Set – Annexure-2
3. Validation Summary Report – Annexure-3

8. References

• USP <797>: Pharmaceutical Compounding—Sterile Preparations
• ICH Q1A(R2): Stability Testing of New Drug Substances and Products
• FDA Guidance on In-Use Stability Testing of Drugs

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name	Ajay Kulkarni	Poonam Desai	Sunita Reddy
Designation	Formulation Analyst	QA Reviewer	Head – AMD
Department	Analytical Method Development	QA	Analytical Method Development

11. Annexures

Annexure-1: API-Diluent Compatibility Log

Sample ID	Diluent	Time (h)	Appearance	Assay (%)	pH	Status
ACT-274-01	0.9% NaCl	24	Clear	98.7	6.2	Pass

Annexure-2: HPLC Chromatogram Set

Overlay chromatograms for API in each diluent across 0–48 hour time points confirming peak stability and retention time consistency.

Annexure-3: Validation Summary Report

Method validated for API-diluent compatibility across three injectable APIs. Linearity, precision, and robustness confirmed for assay under various conditions. Visual and pH results indicated no significant degradation or interaction.

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
21/05/2025	2.0	Added robustness and particulate criteria, updated diluent types	Annual Review	Sunita Reddy
15/04/2022	1.0	Initial SOP Release	New SOP	QA Head