Capsule method development

[lcrandall]

Hi all,
I'm having a bit of a quandry with a method for powder in capsule stability. It's been a while since I've worked with capsules and I'm wondering if I've forgotten something big.

The API is VERY water insoluble.
The API is fluffy and low dose...I've used "open capsule, empty contents into flask" method before, but here I lose the API.
The capsule shell is not dissolving in ACN after much sonication. I've also tried to add water up to 5%, but the capsule still isn't dissolving.
We don't have many capsules, so I don't want to turn the method into "dump capsules and weight out x mg into a vol flask".

I hope I've given all the necessary details. Any suggestions would be appreciated.
Thanks!

[Dan]

lcrandall,

From your description, I will assume that you have a hard gelatin capsule. This is important as the sample preparation can be very different for soft and hard gelatin capsules.

As you noted, the capsule shell doesn't dissolve/disintegrate in organic solvent. It won't as it is designed for the aqueous environment of the body; if the solvent is too high in organic content , then the shell will remain intact and not release its contents.

Suggestions:

1) Try a sample solvent that is mostly aqueous and has a surfactant that will solubilize your API.
2) Try a two-step solvent addition for the sample prep. First add a bit of aqueous solvent to get the shell to disintegrate. Then add the organic solvent to extract/dissolve your API.
3) Use an erlenmeyer flask (or other suitable extraction flask) not a volumetric flask. Many sample preps that I have seen make use of the volumetric flask, but that is not suitable for the preparation of capsules. You just don't get good extraction/disintegration/mixing with the volumetric flask for capsule sample preparation.
4) Test your sample preparation with aged capsules as the shell can undergo physical changes with time that make it harder to disintegrate. (You can approximate 2 years of real time at room temperature by placing capsules at 60 degrees/60%RH for 2 weeks.)

One added note, if you use suggestion 2 above, then you should consider the volume change for mixing water and orgainc. There was a discussion thread about that subject on this forum a few months ago.

Regards,
Dan

[lcrandall]

Thanks for the suggestions.

I think these may be very old capsule shells. All my experience is with soft capsules. But, I'm having a difficult time even getting the shells open. Some are ok, and some are beastly!
And, I tried to get an empty shell to dissintegrate in water. I soniccated, shook, and vortexed the solution and the capsule just swelled and stayed intact. Does anyone have any comments/experience with this problem? My theory is that they sent me very old capsules that have cross-linked.

The next is a philosophical question.. when working with capsules in erlenmeyers or such, and not in a volumetric flask, how reliable is measuring volume with a graduated cylinder?

Thanks!
Lisa

[DR]

It's unreliable - you have to do a transfer, rinse, transfer that, repeat - into a larger volumetric, then QS.

40°C water and a little sonication as a first step should open up the capsules. If it doesn't, you may want to reconsider your capsule materials or vendor.

[Dan]

Lisa,

OK, so it is soft gelatin capsule shells. Since you mentioned that your API is "fluffy" I assumed that the shell contents were in powder form and that meant you had a hard gelatin shell. When I think of soft gelatin shells, I usually see liquid contents. But that is not always the case.

Yes, cross-linking is an issue with soft gelatin shells. The older the product, then the more cross-linking that will/can occur. I have seen instances in dissolution analysis where the soft gelatin capsule in the vessel has grown to the size of a golf ball and still not ruptured.

I have never tested it, but I have heard that adding pepsin to the dissolution media allows you to overcome the cross linking problem. See this link at the Dissolution Discussion Group for a discussion on this topic:

http://www.dissolution.com/vbulletin/sh ... php?t=2319

It has been some years since I last worked with soft gelatin capsules, but I remember that for the assay analysis, we always cut open the shells for the sample preparation. You use a razor blade or similar device. You need to carefully rinse the razor blade and shell to ensure that all contents get into your preparation flask. You mentioned that your API gives problems if you do this, so it doesn't seem to be an option.

Perhaps, using some pepsin will work for your case. You will still need to have a two-step solvent addition in your extraction; water (with pepsin) first, followed by addition of organic as I noted before.

Usually, you need better accuracy for the solvent delivery in the sample preparation than you can get with a graduated cylinder. I don't recommend its use in this situation. Also, you will come across the occasion when an analyst uses a TC graduated cylinder instead of the more common TD one and then the volume error throws off the results; OOS investigations are a pain.

Regards,
Dan

[ym3142]

I think it is not necessary to dissvole the capsule. Open it, put the whole to flask, let the solvent dissolve the API.

[lcrandall]

I had wanted to try to dissolve it since my API can be difficult to work with.
But...
What do we think about opening capsules over weigh paper, then dumping into a VF, and rinsing paper very well into the flask? The capsule shell halves would also be dropped into the VF.
Thanks!

[Dan]

What do we think about opening capsules over weigh paper, then dumping into a VF, and rinsing paper very well into the flask? The capsule shell halves would also be dropped into the VF.

That could work. You could also use a powder funnel instead of the weighing paper. The funnel could be placed directly into the neck of the volumetric flask.

If you have a soft gelatin capsule shell and you are using a volumetric flask, then you may need to correct the final sample preparation volume for the volume of the shell. This would only apply if the shell does not dissolve. If it is only one capsule shell, then the volume may not be significant enough to require a volume correction.

We had an assay method using 10 capsules and the soft gelatin did not dissolve and the volume was significant so a volume correction was used.

Regards,
Dan