Drug Urinary Excretion Data—some Aspects Concerning the Interpretation

The study of the excretion of a drug and its metabolites in urine after drug administration can provide valuable information concerning drug absorption, distribution and elimination. The maximum value of these studies is, however, only obtained by a detailed kinetic analysis of the experimental results. While certain procedures may be preferable for a specific purpose, two methods of treating the experimental results are capable of general application and are suitable for mathematical interpretation. The first is derived from the classical method of chemical kinetics. In principle it seeks to calculate the amount of drug in the body from a knowledge of the amount of drug excreted at that time and the total amount finally excreted. Its application to drug urinary excretion data will here be termed the " Sigma-minus" method. The second is the " Rate" method. This is based on a study of the decline in the rate of excretion of drug in the urine.