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OOS Investigation Tools: A Comprehensive Guide

Introduction In the pharmaceutical industry, Out-of-Specification (OOS) events can have significant consequences, impacting product quality, patient safety, and regulatory compliance. Effective OOS investigation is crucial to identify the root causes, implement corrective actions, and prevent future occurrences. This blog post will explore various tools and techniques employed in OOS investigations. Essential Tools for OOS Investigations Data Analysis Tools: Statistical Software: Leverage software like Minitab, Excel, or specialized statistical packages for data analysis, trend identification, outlier detection, and process variability assessment. Quality Management Systems (QMS): Utilize QMS software to centralize and manage quality data, facilitating efficient data retrieval, analysis, and reporting during investigations. Electronic Batch Records (EBR): Employ EBR systems to capture and store detailed manufacturing process information, aiding in tracing back steps, identifyi

DHS | Depyrogenation Tunnel Principle

DHS | Depyrogenation Tunnel Principle

DHS (dry heat sterilization) is a method of sterilization and depyrogenation tunnel work on DHS principle. The depyrogenation process is widely used in the pharmaceutical industry. The term depyrognation refers to the removal of pyrogens. The injectable products are filled in the glass vials/ ampoules. Injectable products are said to be pyrogen-free products. 

Hence the glass vials and ampoules are subjected to depyrogenation in the depyrogenation tunnel. For the preparation of injectable products, Water for injection is used. Water for injection is free from pyrogens / bacterial endotoxins. Hence, before manufacturing injectable products, pre-sterilized articles are used, and finally, all assembled products are subjected to terminal sterilization. This topic is too vast and interconnected with each process. So in this post, we will know the " what is depyrogenation and depyrogenation tunnel principle".

DHS (Dry heat sterilization)

The dry heat sterilization process is performed by conduction; that is where heat is absorbed by the exterior surface of an item and then passed onward to the next layer. Eventually, the entire item reaches the proper temperature needed to achieve sterilization. The proper time and temperature for dry heat sterilization is 160 °C (320 °F) for 2 hours or 170 °C (340 °F) for 1 hour or in the case of High-Velocity Hot Air sterilizers 190°C (375°F) for 6 to 12 minutes

What Is Depyrogenation? What Is Depyrogenation Tunnel (DHS)?

Depyrogneation tunnel is used for the removal of pyrogens / bacterial endotoxins from the subjected glass vials/ ampoules before product filling. Depyrogenation tunnel works on the 6 log reduction principle. The glass vials/ ampoules are subjected to temperatures of more than 300°C for a specific time. The depyrogenation is meant for the removal of microorganisms only, but heat-resistant microorganisms such as bacterial endotoxins/pyrogens are not killed by sterilization. Hence this endotoxin removal process is called depyrogenation.

What Are Pyrognes? What Are Bacterial Endotoxins?

Pyrogens are substances that can produce a fever. The most common pyrogens are endotoxins, which are lipopolysaccharides (LPS) produced by Gram-negative bacteria such as E. coli. Examples of pyrogen-producing gram-negative bacteria are Escherichia coli (E. Coli), Proteus, Pseudomonas, Enterobacter, and Klebsiella

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How does depyrogenation tunnel work? How does DHS work? What is the depyrogenation process?

The depyrogenation tunnel has two machines. 1st is the vial washing machine and 2nd is the depyrogenation tunnel. These two pieces of equipment run parallel. 


1. Inspected good vials/ampoules are passed on the conveyor.

2. Vial washing machine operation: 

Vials/ampoules are then subjected to the washing machine. In this step, the vials are washed with purified water (Externally)- dried with compressed air (Externally)- again washed with recycled water (Internally) - again dried with compressed air (Internally)- Again washed with water for injection (Internally) - and dried with compressed air and finally, these dried vials are passed to tunnel through the conveyor.


3. Depyrogenation Tunnel Principle: 

The tunnel has 3 zones, 1st is preheating zone, 2nd is the depyrogenation zone and 3rd is the cooling zone. 

  • The vials are passed to the preheating stage at a temperature of -----
  • After preheating, the vials are passed to the depyrogenation zone of temperature NLT 300°C for a specific time, The time temperature is based on validation study and it can vary based on the vial size. Only consider that more the vial size the time required for sterilization is less, and smaller vial size time required for depyrogenation is more.
  • After depyrogenation, the vials are cooled in the cooling zone at 30 to 40°C.
  • These vials are called depyrogenated vials. For a better understanding of the working of the depyrogenation tunnel principle have a look at below depyrogenation tunnel animation.

Does Depyrogenation Sterilize?

Depyrogenation is one type of sterilization only. However, only steam sterilization does not remove all the microorganisms eg. E.coli, Proteus, Pseudomonas, Enterobacter, and Klebsiella. As steam sterilization is a moist heat sterilization technique only heat-labile microorganisms are killed by this process. However, for heat resistant microorganisms higher temperature exposure is required and this process is called depyrogenation and terminal sterilization.

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Conclusion on Depyrogenation tunnel (DHS):

Depyrogenation tunnel is a type of dry heat sterilization method. It is used to remove pyrogens from the objects like glass vials. The heat-labile products can not be subjected to dry heat sterilization. It also gives more than 6 log reduction as sterility assurance level. Hence this method can be used for continuous decontamination activity of glass vials, stoppers that are heat resistant. 

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