The first-order elimination rate constant of the metabolite is the rate constant responsible for the elimination of the metabolite from the body. This rate constant is dependent on the clearance and the volume of distribution of the metabolite. (CL_T(m)) / Vd_(m) = k_(m))

The elimination rate constant of the metabolite is the same when the metabolite is formed in vivo after the parent drug administration and after administration of the preformed metabolite.

This constant represents the metabolite elimination through all routes of metabolite elimination including secondary metabolism and renal excretion.

The first-order elimination rate constant of the metabolite has units of time ^-1.

The metabolite half life is the time required for the amount of the metabolite or the plasma concentration of the metabolite to decrease by 50% . The half life has units of time.

The metabolite half life and the metabolite first order elimination rate constant are dependent on the metabolite total body clearance of the metabolite volume of distribution.

The half life of the metabolite is constant within a patient (dose and concentration independent) when the metabolite elimination process follows first-order kinetics. However different patients may have different half lives for the same metabolite.

The half life is the time required for the amount of the drug or the plasma concentration of the drug to decrease by 50%. The half life has units of time.

The half life and the first order elimination rate constant are dependent on the total body clearance and the volume of distribution.

The half life of a drug is constant within a patient (dose and concentration independent) when the drug elimination process follows first-order kinetics. However different patients may have different half lives for the same drug.

The half life is a very important parameter, because it indicates how fast the drug is eliminated from the body. Drugs with shorter half lives are eliminated faster than those with longer half lives.

The semilog graph paper allows plotting the data at logarithmic intervals without doing the actual logarithmic transformation of the numbers.

In order to determine the slope of a line drawn on a semilog graph paper it is necessary to do logarithmic transformation of the y values. The slope of the line in this case will be determined from the following relationship: