Back to the Top
Dear all,
In a tissue distribution study, rat liver was collected which weighed
8.33 g. 0.5 g rat liver was homogenised in 5 ml homogenising solution,
0.5 ml of the homogenate was processed, assayed along with calibration
standards processed similarily and calculated concentration was 74.03
ng/ml. How should I proceed to calculate the drug content in ng/g in rat
liver?
Thank you in anticipation,
Hari
Hari Narayan kushwaha
SRF, Central Drug Research Institute,
Lucknow-226001,
India
Back to the Top
If you weigh the homogenate taken for assay will be able to calculate
the concentration of drug in ng/g of tissue
Back to the Top
The following message was posted to: PharmPK
Dear Hari,
Concentration: 74.03 ng in 1 mL of homogenate
-> 37.015 ng in 0.5 mL of homogenate
-> 370.15 ng in 5 mL of homogenate
-> 370.15 ng in 0.5 g of rat liver
-> 740.3 ng per g of rat liver
Does this make sense?
Cheers,
Fabrice
Fabrice Nollevaux,
Arlenda SA
www.arlenda.com
Back to the Top
Dear Hari
74.03 ng/ml means 370.15 ng in 5 ml of homogenate or 0.5 g of rat
liver, therefore in 1 g of liver there is 370.15 X 2 = 740.3 ng of drug
-
Garima Balwani
Research Scholar
Department of Pharmacy
BITS-Pilani
Back to the Top
Hello Hari,
Though the solution is not hard, it is not quite straightforward. The
comment by msgcot2 has merit, but beside the weight of the homogenate
taken, you would need the weight of the entire homogenate. You could
also use volume measurements for the homogenate and the sample analyzed.
You indicate that the tissue was homogenized in 5 mL of homogenizing
solution. One assumes that you then have 5 mL + 0.5 g of tissue, so the
volume of the homogenate is greater than 5 mL. So you need to have an
estimate of the total volume or mass of the total homogenate. One might
assume that all tissue has a density of 1 but that in not correct, so
mass and volume may not be the same. I suspect that 0.5 g of lung
tissue and 0.5 g of muscle will have different volumes. So to determine
the concentration of drug in a tissue from the information given, you
would use the following equation:
((concentration in aliquot/volume of aliquot analyzed)*total volume of
homogenate)/weight of tissue homogenized=concentration in tissue.
Again you could use mass or volume for the size of the sample analyzed
and the total homogenate. Fabrice's estimate of 740.03 ng/g liver is
likely pretty close. However, Fabrice assumes that that total volume of
homogenate is 5 mL. I suspect that is is higher. You would need that
additional information to accurately calculate the concentration in the
tissue. You may have a further error in that the concentration in the
tissue may not be homogeneous. Your sample may have higher a higher or
lower concentration than the total liver.
Good Luck,
Chris
Christopher Town, PhD
Home EMAIL: town.chris.-at-.sbcglobal.net
Back to the Top
Dear Hari,
Please go through the below calculation carefully, you will get the tissue
concentration in ng/g appropriately.
Consider 0.5 g of liver weight as 1 part. You have added 5ml of homogenising solution
which is equivalent to 10 part of tissue weight. Now add both the part to find dilution
factor i.e., 1+10=11. Calculated concentration was found to be 74.03 ng/ml. Now multiply
this value with dilution factor i.e., 74.03*11=814.33 ng which is present in 0.5 g of
tissue. So, 1g of liver tissue contains 814.33/0.5=1628.66 ng/g of liver tissue.
I think the above calculation will give appropriate conc. per g of tissue. But to find
exact conc in tissue always homogenize the whole tissue not the some part of tissue. This
will give exact amount of drug present in the tissue
Regards,
Nirat P. Shah
Scientist II
ADME Dept.
Torrent Research Centre,
Gandhinagar-382428
Back to the Top
The following message was posted to: PharmPK
Dear Hari,
I agree with Nirat, but when we are looking for exact concentration of
test article in tissue then we have to apply correction factor of test
article in tissue residual blood fraction.
It has greatly influence the results for the test article whose tissue
to plasma distribution ratio is very high or very low in highly perfused
tissues like lung, liver, kidney, etc.
Best Regards,
Mr. Dipak Modi
Associate Scientist
Pharmacokinetics and Metabolism
Novel Drug Discovery & Development
Lupin Research Park
46A/47A, Village: Nande, Taluka: Mulshi
Pune-411 042, India
Back to the Top
Hello Narat and Hari,
I would maintain that the best estimate will be arrived at by measuring the volume or mass
of the whole homogenate and the corresponding volume or mass of the homogenate sample that
was analyzed. In adding 5 mL of a solution to 0.5 g of tissue and homogenizing, it is not
likely that you will obtain exactly 5.5 mL of homogenate. There are fats, solids and
other components in the sample that will likely prevent that. However, using a factor of
11 is going to give a better answer than a factor of 10, because you should obtain a
volume closer to 5.5 mL than 5.0 mL.
The remaining issue with your answer is the number of significant digits. I know that
this has been covered in previous discussions on this Listserve. However, in multiplying
by 11, a number that you have little precision for, you went from 4 to 5 significant
figures in you answer. In dividing by 0.5 (which you had a better value but not to 5 or 6
significant figures) you went to 6 significant figures I think that when you make your
assumptions, you might want to give your answer as 1.6 X 10^3 ng/g liver tissue. The rule
of thumb for significant figures (that I was taught) is that you should match the number
of digits in your answer with that from the factor with the lowest number of significant
figures. I think that two would be a reasonable number of significant figures in this
case. I know that we all want to keep the number of decimal places constant throughout our
calculations, but there are times, when for accuracy, we should admit that we can't
justify that number of significant digits. I would be interested in the comments of
others on this issue.
Best Regards,
Christopher Town, PhD
Independent Consultant
Home EMAIL: town.chris.at.sbcglobal.net
|
Want to post a follow-up message on this topic?
If this link does not work with your browser send a follow-up message to PharmPK@boomer.org with "Calculation of drug concentration in tissues" as the subject | Support PharmPK by using the |
Copyright 1995-2011 David W. A. Bourne (david@boomer.org)