Clearance (More...)

Nonrenal Clearance:

Clearance by the fecal route (ClF), respiratory route (ClL), salivary route (ClS), biliary route (ClB), can
be computed in a fashion analogous to computation of ClR: measuring the amount of subtance excreted
in the feces, expired air, saliva, etc., over an interval and dividing by the plasma concentration at
mid-interval and the length of the interval. Following oral administration of a substance, measurement
of fecal clearance may be confounded by the presence, in feces, of unabsorbed substance or of
substance absorbed but excreted into the lumen of the gastrointestinal tract in, e.g., bile. Specialized
techniques exist for estimating clearance of substances by the liver (ClH), by biotransformation and/or
biliary excretion.

Unlike half-lives, clearances are directly additive and for any substance:

ClT = ClR + ClL + ClH + ClS + ClF + . . . etc.