Is this the situation?

A blood test has measured the level of Soma (carisoprodol) in
blood of 26 micrograms per millilitre, and you wish to know
what dosage of the drug the person must have taken to account
for this?

If that is so, it is a relatively complex question of
pharmakokinetics. To address it, the most important additional
piece of information required is the time between the drug
having been taken, and the blood test having been performed.
It is also important to know if the scenario is of a person
regularly taking the drug at a known dosage (if so, what
dosage?) who may have taken a single wrong dosage, or a
person who had not been taking the drug before and who had
taken a single dose.

If you could supply, confirm, or correct those points, we will be
in a much better position to find an answer for you.

OK - and was it a person who had already been taking the drug,
or just a single dose?

This is a comparatively short time and depending on the exact
mode of uptake for this drug (which I haven't explored yet), it
may not have reached its peak concentration.

Perhaps I misunderstood your initial question. Do you actually
know what dose you took?

OK - my answers stand up reasonably well given that you took
about 1400 mg. The dose/concentration relationship could
easily be non-linear. That is one of the reasons why
extrapolation can be inaccurate.

The comments of level versus driving impairment still apply.

If it was not under your doctor's specific direction that you took
this dosage, then of course, you would not have a case there. I
had thought that it was while you were at the doctor he or she
might have said something like "OK - take 6 soma now and that
should help".

I have given my opinion on this, and a great deal more
information, in the formal answers I have posted here.

To access them, you must pay the required site deposit. If you
find the formal answers to be sufficiently helpful, you should
then accept them in order that I can receive payment for my
efforts.