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# Calculating Drug concentrations in Log scales

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### #1 Peniel

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Posted 03 April 2013 - 02:14 AM

Dear all,

I worked out how to carry out my MTS assay drug concentrations as 10uM, 20uM, 30uM, 40uM, 50uM, 60uM, 80uM and 100uM. I was just told it is better to work in log scales for drug concentrations and I have no clue on what to do. I am just confused. Please help!!!

### #2 mdfenko

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Posted 03 April 2013 - 06:48 AM

log scales are 10-fold differences between doses.

you can do more than one dose within each log (eg 1, 2, 5, 7.5, 10, 20, 50, 75, 100, 200, 500, 750, ...)

Edited by mdfenko, 03 April 2013 - 06:50 AM.

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### #3 Tom M

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Posted 03 April 2013 - 07:13 AM

You might also try concentrations that work out to "half log units", which would help linearize your concentration-response curves, ie. 1, 3, 10, 30, 100, 300 etc.

### #4 Peniel

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Posted 03 April 2013 - 10:40 AM

log scales are 10-fold differences between doses.

you can do more than one dose within each log (eg 1, 2, 5, 7.5, 10, 20, 50, 75, 100, 200, 500, 750, ...)

Thanks mdfenko.

I don't know how to work this out. What I'm thinking is if my first concentration is 100nM then the log10 will be -7? Do I work then work from that in log scale i.e -6, -5, -3, -1, 0.01, 0.1, 1, 10.

I want to work within the range of 100nM to 10uM. Please I'll need some elementary explanation as I am rubbish at this.

thanks

### #5 Peniel

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Posted 03 April 2013 - 11:30 AM

log scales are 10-fold differences between doses.

you can do more than one dose within each log (eg 1, 2, 5, 7.5, 10, 20, 50, 75, 100, 200, 500, 750, ...)

Thanks mdfenko.

I don't know how to work this out. What I'm thinking is if my first concentration is 100nM then the log10 will be -7? Do I work then work from that in log scale i.e -6, -5, -3, -1, 0.01, 0.1, 1, 10.

I want to work within the range of 100nM to 10uM. Please I'll need some elementary explanation as I am rubbish at this.

thanks

I think I got that all wrong.
so for 1uM it'll be 0.01 in log scale. So I can do 0.01, 0.10, 0.30, 0.40, 0.50, 0.60, 0.65, 0.70, 0.80 and it will be equivalent to (uM) 1.02, 1.23, 1.995, 2.511, 3.162, 3.98, 4.67, 5.01, 6.31 and so on. Does this sound right?

### #6 Tom M

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Posted 03 April 2013 - 01:18 PM

If you wish to run a curve between 100 nM to 10 uM and generate a "linear" log scale then try these concentrations: 100 nM, 300 nM, 1uM, 3uM and finally 10 uM. That will yield values on the x-axis of (log molar) -7, -6.5, -6, -5.5, -5, -4.5; respectively.

### #7 Peniel

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Posted 03 April 2013 - 02:12 PM

If you wish to run a curve between 100 nM to 10 uM and generate a "linear" log scale then try these concentrations: 100 nM, 300 nM, 1uM, 3uM and finally 10 uM. That will yield values on the x-axis of (log molar) -7, -6.5, -6, -5.5, -5, -4.5; respectively.

Thank you so much Tom, I appreciate this. How does this relate to log10 values. One of my peers keep emphasizing 0.001, 0.01, 0.1, 1.0, 10, 100, 1000. Sorry this questions might seem stupid or basic but I have no clue.

Thanks

### #8 mdfenko

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Posted 04 April 2013 - 04:50 AM

your peer is correct. as i wrote before, logarithmic differences in doses refers to 10-fold differences between samples. sorry if tom m and i confused you by showing how to get better coverage while still performing logarithmic changes.

in fact, if you first perform just 10-fold doses, then you can narrow the doses after finding the best range.
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### #9 Peniel

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Posted 06 April 2013 - 02:45 AM

### #10 murusa

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Posted 31 August 2015 - 06:12 PM

the topic is very old but there is a LOG10 function in the Excel software. you can easily calculate the log10 value of your concentration.