A first-order process is a process that has a rate proportional to the amount of the reactant involved in this process.

For example, if the dg elimination rate is proportional to the amount of the drug in the body, this means that this drug is eliminated by a first-order process. The proportionality constant is the first-order elimination rate constant. i.e.

Elimination rate = elimination rate constant x drug amount

The rate of drug elimination decreases with time because the amount of the drug remaining decreases with time.

The volume of distribution is the apparent volume in which the drug can distributed in. It is the parameter that relates the amount of drug in the body to the concentration of the drug in the sampling site. It is not an actual volume, however it is a hypothetical volume determined by the drug distribution behavior.

The volume of distribution ranges from 3-5 liters to more than 25 L/kg. Drugs with higher affinity for tissues, have higher volume of distribution.

It is the volume of the plasma or the blood that is completely cleared from the drug per unit time by the kidney. It has units of volume/time.

The renal clearance cannot exceed the CL_T. However it can be equal to the CL_T when the drug is excreted completely unchanged by the kidney.

The renal clearance can be determined from the renal excretion rate over a short interval and the average plasma concentration during this interval.

A rectangular graph paper is a graph paper where the x-axis and the y-axis are divided into equal divisions. Each of these divisions represents a fixed value throughout the x or the y axes (linear scale).

The x-axis and the y-axis may cover different ranges of the graphed variables. The minimum value on the axes may or may not be zero.

It is the volume of the plasma or the blood that is completely cleared from the drug per unit time by the kidney. It has units of volume/time.

The renal clearance cannot exceed the CL_T. However it can be equal to the CL_T when the drug is excreted completely unchanged by the kidney.

The renal clearance can be determined from the renal excretion rate over a short interval and the average plasma concentration during this interval.