Gramicidin

[Andrea Hilton]

Dear members,

Does anyone have a suggestion of a HPLC method for gramicidin assay in ointments and creams? I was trying to develop it as per USP 28 but I am having problems with getting growth response in the turbidimetric microbiological assay.

Regards,

Dea Hilton

[Rick Jagielski]

Our Micro lab also struggles with the Gram assay per USP. It turns out that the issue with the USP method is that it incorrectly lists the times for growth of the organism. We had to map a growth curve and revise our incubation/introduction times accordingly. If we followed the USP method the organism was already into it's death phase.

The problem with an HPLC method and the reason we haven't gone to one is that the label claims are often based on A.U. or active units. You can quantify the concentration but it doesn't tell you the activity of the material.

We have often resorted to sending samples for bulk release out to Nucro Labs in Canada to have the microbiological assay done. 2-3 wks turnaround.

If you have some way to resolve activity of the material to its concentration we would be very intrested also.

Thanks
Rick

[Andrea Hilton]

Dear Rick,

I'd studied the problem with our Micro lab and the analyst responsible for it guaranteed me that there are no problems with the times for growth of the organism. The USP method is working for the raw material. He had already map a growth curve and the microorganism can't survive since the beggining of the test.

I don't have a problem with using an HPLC method because the label clains in my country is based on mg per g of the productand I don't have to quantify the activity of the material. I don't know also a way to resolve your problem, but I'm doing a lot of research on this and when I have the solution for these problems, I'll let you know.

So can anyone (even you, Rick), have another suggestion?

Kind regards,

Dea