The validity of this depends on the constancy of renal clearance and the quality of the urine excretion data. This is one method that can be used to check for long terminal half-lives which are not evident from the plasma data, provided the two criteria mentioned above are fulfilled. A good deal of our research involves following the excretion rates of drugs because we do not have the facilities for taking blood samples from human volunteers. The assumption that must be met for urinary analysis is that drug is excreted from the central compartment by a definable process, usually first order. Set up your spreadsheet with columns for time, midpoint, volume, and concentration.
Time is the time since the dose was taken.
Concentration is determined in the normal manner by HPLC or whatever instrument you use. Some spreadsheets can't handle subtracting a cell from the next one in the column. We have used this fact in the formulation of several bioequivalent products under the assumption that if two formulations are bioequivalent, then they should be excreted in a bioequivalent manner. I said previous compartment. If you are measuring a drug that is excreted intact, then the input calculated by deconvolution is input into the central compartment.