Hi,

we have validated a HPLC method for procaine at a wavelength of 280 nm in a product, called A.

Now we use the same method for benzylpenicilline, procaine and DHS in another product, called B.
This detection wavelength is set at 200 nm.

Question: Is it allowed to use for product A a wavelength of 200 nm (linearity is tested with the validation of the method for product B). The method is specific for both products, precision is tested, everything is tested. We just want to change the wavelength, is this allowed?

It would depend on what method you submitted when you submitted your NDA(or ANDA). You need to stick to that one, or you would have to modify your submission.

We have submitted our first method, so we have to modify/adjust our method. But what parameters should we test before changing our method, or should we revalidate the entire method?

You would have to revalidate the entire method, in my opinion, to change something as crucial as wavelength.

Hi Mel,

Is a wavelength that crucial? We have tested specificity, so there are no peaks in the background, wich can cause errors at different wavelengths. Also we have tested lineairity at the 200 nm wavelength method, so thats no problem too. My question: is a wavelength in this case that critical?

Consider the effect of changing the wavelength:
The extinction coefficient is likely to be different at different wavelengths, so sensitivity could be much less or much greater. This could affect the range of the method and the linearity. At 200 nm, the background noise could be much higher -- the mobile phase may even be opaque! -- which could effect quantitation limit (range), accuracy and precision.

Furthermore, you speak of validating the method for procaine, but using it for two other analytes as well. It must be validated for those, too.

As far as the procaine is concerned, you might want to consider a dual wavelength detector so you can go back to measuring that at 280 nm and not have to revalidate the method for that component, at least. For the investment in such a detector, you avoid the cost of revalidating. Probably a significant savings.

If I understand this well, I just have to validate the accuracy, precision and quantitation limit for the method @ 200 nm.


So: We have validated our method @ 200 nm for product B so the linearity, precision and accuracy is validated. Specificity is also tested for product A. Does this mean that we don't need to revalidate our method for product A?

Bite the mini-bullet and get either a multiple wavelength detector on one such as Agilent VWD where you can time-program in a wavelength switch automatically. Whatever you do, document the changes, and do what you document. The FDA won't buy the "being cheap" excuse, it's the cost of being in the pharmaceutical business.