Standard Operating Procedure for In-Process pH Testing for Enteric-Coated Tablets

Department	Quality Control
SOP No.	SOP/TAB/125/2025
Supersedes	SOP/TAB/125/2022
Page No.	Page 1 of 6
Issue Date	01/03/2026
Effective Date	06/03/2026
Review Date	01/03/2027

1. Purpose

To define the procedure for conducting in-process pH testing on enteric-coated tablets to ensure the coating’s acid resistance and its ability to protect the tablet core from gastric fluids.

2. Scope

This SOP applies to in-process pH testing of enteric-coated tablets to ensure that the coating remains intact and functional under acidic conditions, preventing premature dissolution in the stomach.

3. Responsibilities

• Quality Control (QC): Responsible for performing pH testing on enteric-coated tablets during production to verify coating quality and functionality.
• Coating Operator: Responsible for ensuring that the enteric coating process is carried out as per the defined parameters and ensuring that the tablets are sampled for pH testing at the appropriate stages.
• Quality Assurance (QA): Ensures that pH testing procedures are followed as per this SOP and reviews the results for compliance with required specifications.

4. Accountability

The QC Manager is accountable for ensuring that the in-process pH testing of enteric-coated tablets is performed consistently and according to this SOP. The QA Manager is responsible for reviewing pH testing results to ensure compliance with internal and regulatory standards.

5. Procedure

5.1 Sample Collection

1. During the enteric coating process, collect a representative sample of tablets at regular intervals, typically every 30 minutes or after every 100 tablets produced.
2. The sample size should consist of at least 10 tablets for accurate pH measurement.

5.2 pH Testing

1. To measure the pH of the enteric-coated tablets, prepare a suitable acidic medium (typically a 0.1 N HCl solution) that simulates the stomach’s pH (approximately pH 1.2).
2. Place a tablet in the acidic medium and allow it to dissolve for 30 minutes at 37°C (simulating gastric conditions).
3. Measure the pH of the solution after the prescribed time using a calibrated pH meter.
4. The pH of the solution should be monitored to ensure that it remains within the expected range, with no premature dissolution of the enteric coating occurring before the tablet reaches the small intestine (i.e., the pH should not drop below the threshold for dissolution of the enteric coating, typically around pH 5.5-6.0).
5. Record the pH values and any changes during the test.

5.3 Monitoring and Adjustments

1. If the pH measurement shows that the coating is dissolving prematurely (before the tablet reaches the small intestine), adjust the coating process parameters, such as spray rate, drying temperature, or tablet rotation speed, to ensure uniform and effective coating.
2. Re-sample and test the tablets again after adjustments have been made to verify that the coating now meets the required standards.

5.4 Monitoring Frequency

1. pH testing should be conducted at regular intervals during the enteric coating process, typically every 30 minutes or after every 100 tablets produced, to ensure consistent coating quality.
2. If any irregularities or deviations are found, increase the frequency of pH testing until the issue is resolved.

5.5 Documentation

1. Record all pH test results, including the individual pH readings, the time of collection, the batch number, and any corrective actions taken in the batch record (Annexure-2).
2. Document any deviations from the expected pH range and the corrective actions taken in the deviation report (Annexure-1).
3. Ensure all records are signed, dated, and reviewed by QA for compliance with regulatory standards.

5.6 Acceptance Criteria

1. The pH of the solution should not drop below the threshold pH value for the enteric coating dissolution (typically around pH 5.5–6.0) during the test.
2. If the pH drops too low, the batch may be rejected or reprocessed to correct the coating issue.

5.7 Post-Coating Actions

1. Once the coating has been verified for pH stability, proceed with the next steps in tablet production, such as drying, packaging, or storage.
2. Ensure that any adjustments made to the coating process are documented, and the equipment is cleaned and calibrated as required.

6. Abbreviations

• SOP: Standard Operating Procedure
• GMP: Good Manufacturing Practice
• QC: Quality Control
• QA: Quality Assurance
• API: Active Pharmaceutical Ingredient

7. Documents

1. Batch Record (Annexure-2)
2. Deviation Report (Annexure-1)

8. References

• USP <701> – Disintegration Testing
• 21 CFR Part 211 – Current Good Manufacturing Practice for Finished Pharmaceuticals (US FDA)
• European Pharmacopoeia (EP) – Specifications for Enteric-Coated Tablets

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Deviation Report

Deviation Date	Batch Number	Deviation Description	Corrective Action	Responsible Person
15/12/2025	Batch 001	Premature coating dissolution below pH 5.0	Adjusted coating spray rate and re-tested	Jane Smith

Annexure-2: Batch Record

Sample Number	pH Value	Time of Test	Action Taken
Sample 1	5.8	10:30 AM	Accepted

Revision History:

Revision Date	Revision No.	Revision Details	Reason for Revision	Approved By
01/01/2024	1.0	Initial Version	New SOP Creation	QA Head
01/02/2025	2.0	Updated pH testing process	Improved testing methodology	QA Head