Depyrogenation oven issue

I am having a issue with the depyrogenating of wet vials. A large portion of the vials are coming out scored-scratched. It seems that they are fusing together during the run. Could you provide any suggestions?

Hi MattW,

I think the best way to avoid this is to perform a Dry step prior to beggining the Depyrogenation.
I recommend a 100oC for 1 hour and then begin your Depyrogenation.

May I ask you what is the basis of preheating vials at 100C for 1 hour?
The total time will be extended and it had to be shown to the FDA inspector.

Hi Matt,

That is strange. I won’t recommend a pre-drying phase as it will not eliminate the root cause of the problem.

Are you facing this problem with just one type of vials or all of them including ampoules, if any?

If all types/sizes are having this problem, I suggest you check the water quality which is fusing them together. Or you should consider creating some space in the depyrogenation trays.

Can’t pin point the cause without further details.


I do not think water is a culprit. This particular question is comming from EU zone. Its not a third world country like India/Pak etc. We all believe they adhere to stanadard washing procedures by purified water and then Water for Injection that will adhere to the requirements of EP/USP.

Adhering is a phase change and sticking to each other. Such were observed with Soda lime glasses. We all need to know does this phenomenon happened with one lot or many lots or different lots of Vials that were procured from vendor.
My second question is what should be the legal or Internal limit thickness of each vial and what was the Observed?
Did they test the vials for USP/EP Glass test by powdering these vials? What were the results when it was sampled? What was result after washing and before Depyrogenation? What was the result when these fused cooled vials were taken post Depyrogenation and tested ?

I asked many experts when I met them especially glass manufacturers including best from EU. Every one were astonished and asked about these tests.
Its not the heat element that is causing. It is quality of glass that is being used.
The above tests are very essential.It gives the clue.
What is the product that is formed during heating and destabilising the basic SIO2 in the vial?

I think this is a great discussion and finally the clue will be revealed by Mr.Matt.


You may be right about the nature of glass.

I am surprised that EU glass manufacturers are unaware of the Type tests. If this is the case, how are they claiming (if they are claiming) the vials to be Type I, II, or III !

Anyway, we shall have to wait for a fresh reply from Matt.


I never mentioned that EU manufacturers are un aware of these USP tests. I mentioned in my earlier reply that there are 3 areas of concern where one can find the solution at the end users site of these vials:
1.Pre washing - Testing Vial- This is done during sampling
2.Post washing
3.Post sterlization of the cooled vials.

Any way this question is a big riddle.Any at the end user they have to carry put a Fault Tree Analaysis study and find the solution.
What is that compound making vials unstable when being heated in a Depyrogenating oven?
Its also scorching or charring the vials. Such scorching comes only when fibres are present in vials that carry over from packing or manufacturing materials from manufacturing site of vials. But they will be certainly removed by washing procedures.

Durga sir, also posible cause are:
External drying with compressed air during washing process.
During heat up period (upto 150 °C), the exhaust (percentage should be fixed on validation studies) should be opened. The generated vapor should be goes out like tunnel sterilizer.
Because I have faced the same problem in my previous company (M/s. Venus Remedies Limited) and implement the above conditions.

With Regards,
Sitarama Raju
SMS Pharma