Back to the Top
Hello Everyone,
We are facing an issue with one of research NCEs which is having lipophilic property.
When we are injecting it intravenously to wistar rats, we are not getting enough systemic levels.
The C0 is much more lesser compared to calculated one.
Dosing : Femoral Vein
Blood collection : Jugular Vein
Method of analysis (LC-MS), formulation assay and deposition in various tissues are the factors
which we already investigated for.
We doubt on solubility but how to access this issue?
Please give suggestions if anybody came across such issues.
Thanks in Advance,
Mitul Patel
DMPK
Torrent Research Centre
Back to the Top
Mitul,
The best advice I can give you is to go and talk to your team's chemist.
If you don't have one, get one.
Dario
Back to the Top
Mitul,
Since your drug is lipophilic, it should easily get into the the organic solvent during extraction.
So, extraction should not be an issue.
If your formulation is stable and clear during iv injection, then solubility should not be an issue.
I would suggest to check Blood-Plasma partition of the drug and plasma stability. If you are
analyzing plasma levels, you need to make sure if drug is partitioned well between blood and plasma.
If your drug is partitioned into blood, then you have to analyze whole blood. Another possibility is
your drug is readily metabolized or transformed which you have not detected
Sukesh
Back to the Top
Hi Mitul,
Have you explored the solubility and permeability profile of the drug? Also I would suggest to see
how much is the drug partitioning into red blood cells. Whether it is hydrophobic or lipophilic as
both are different terms?
Thanks,
Back to the Top
Hi Mitul,
There are at least four possible explanations for what you have described (in order of likelihood):
1. Your compound has poor aqueous solubility, and it just crashes out of solution the instant it
touches blood. If this was the case, you would find high concentrations in the lung, as the
precipitated drug particles are quickly filtered by the small capillaries in this organ. I would
recommend serial diluting your formulation in PBS or other aqueous buffer to at least 6 steps and
look for any evidence of compound precipitation.
2. Your compound is rapidly metabolized in whole blood. You could do in vitro stability in blood
to test this.
3. You are analyzing plasma, but your compound is partitioning into red blood cells. You can do in
vitro blood to plasma portioning experiments to assess this.
4. Your compound has an exceedingly high volume of distribution, such that the measurable
concentrations in plasma are very low. (you didn’t say how low the concentrations actually were).
Hint: It's almost certainly number 1.
Good luck,
Peter
Back to the Top
Thanks a lot everyone for your suggestions.
Peter,
I would like to share few more details.
Compound is not getting partitioned in to RBC, we already ascertained this possibility, so whole
blood analysis will solve this mystery.
Secondly, I agree that compound has got very low aqueous solubility,but atleast it must be get
detected in any matrix either in any tissue or in plasma. Even if there is a precipitation
immediately after coming in contact with blood, it is there in the blood only.
Lastly it is moderately stable in vitro, so instant clearance is not expected.
Regards,
Mitul Patel
Back to the Top
Hi Mitul,
Where did you get the predicted Co? Are you extrapolating from another in vivo study that used this
same compound in the same formulation?
What is the vehicle for the drug? Are you using PEG, for example, which can interfere with mass spec
analysis? If so, a heated nebulizer source may work to reduce this effect compared to turbo ion
spray source on the LCMS.
What exactly does the profile look like? Is it a typical IV profile with the Cmax at the first time
point? Does the Cmax occur later? What are your timepoints?
Could you be getting non specific loss of the drug during dosing, during sample collection, or
sample prep (anything plastic)?
What happens when you test the concentration of your dosing solution in your LCMS assay? Is it
different if you run it through a mock dosing first?
Good luck with your work!
Rachel
| PharmPK Discussion List Archive Index page |
Copyright 1995-2014 David W. A. Bourne (david@boomer.org)