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To Ben Suttle, Zeneca Pharmaceuticals:
I assume your drug of interest is >50% renally cleared, otherwise
what follows is not very relevant.
I don't think you can get around this problem easily since age is one of
the major determinants of declining CrCL after the age of 25 or so.
Furthermore (as you probably know) serum Cr levels can be notoriously
misleading in estimating CrCL in elderly patients, in nutritional
deficiency or metabolic disorders when decreased Cr production by
muscle tissue can mask diminishing renal function.
Therefore, why not be done with it and do a 24 hr urine collection,
a 12 hr serum level and assay both for creatinine to directly estimate the
"true" CrCL? Alternatively, some other direct way to estimate GFR
would be OK, e.g. as suggested in the reply from Michael Burton.
Bruce Charles, PhD
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