Test for Related substance in Drug products containing 3 API

[rickmartink]

Dear Forum
I count upon your knowledge and hope to get a solution.

I have a tablet with composition Paracetamol ( 500mg ) + Aceclofenac ( 100mg) +THiocolchicoside ( 8mg).

Normally for HPLC related substance test , the Final test solution concentration is kept as 1mg/ml. Hence in my case i crush 20 tablets and weigh equivalent quantity of Caffeine to get final concentration of 1mg/ml of Caffeine then the concentration of paracetamol and Aceclofenac will be way too high.

What should i do and which API out of three should i consider to make my test solution.

The HPLC method we have developed is Gradient and we have acheived resolution for all three API so there is no issue with the method we want to use. We have dont on test solution to be prepared.

PL. advice.

Regards
Rick martink

[HPLCaddict]

The HPLC method we have developed is Gradient and we have acheived resolution for all three API so there is no issue with the method we want to use.

Nice. But senseless. What about the impurities? As "related substances test" implies, this is all about the related substances aka impurities, the APIs themselves are quite meaningless. Did you check if all impurities to be measured are resolved from each other and the APIs? Did you perform forced degradation studies?

As for the sample solution, there's no prerequisite that it must be at a concentration of 1 mg/mL. The concentration should be adjusted according to the peak areas you're getting (->response factors!) at the impurities levels you have to quantify.

Do you have specifications for the impurities?

[rickmartink]

The HPLC method we have developed is Gradient and we have acheived resolution for all three API so there is no issue with the method we want to use.

Nice. But senseless. What about the impurities? As "related substances test" implies, this is all about the related substances aka impurities, the APIs themselves are quite meaningless. Did you check if all impurities to be measured are resolved from each other and the APIs? Did you perform forced degradation studies?

As for the sample solution, there's no prerequisite that it must be at a concentration of 1 mg/mL. The concentration should be adjusted according to the peak areas you're getting (->response factors!) at the impurities levels you have to quantify.

Do you have specifications for the impurities?

Dear , please dont think that my query was senseless. i wanted to keep my query short thats why i wrote that we could acheive resolution of APIs. Ofcourse we did degradation studies and resolved all peaks aka ., impurities and APIs. I didnt mention these in my query becoz my query was only on the Sample preparation .
However your second part of reply has was useful to me and has answered me. Thanks a lot.
May i know your email id. I have other doubts and look forward for your advice.

[krickos]

Hi

Not sure I am getting the problem here, you have separation between all peaks of intrest, which is good.

The issue, is it that the 2 most concentrated API peaks goes out of linear range so you can not use internal normalisation (area %)?
If the method is good just use external standards at suiteble concentrations instead.

Another option depending on issue is to use the more concentrated sample preparation for Caffine impurities only and use a diluted sample preparation for the other impurties, but obviously takes more time to run, so not a first choice.

[carlos.teixeira]

You are a hero, Rick, because you have a method for all related compounds of three API. In case you have any coelution you may impróve your method using wavelengths. Take care with the ranges for each related compound in order to avoid some surprises. And go ahead. All the best for and your Team.