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 be distributed in. It is the factor 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.
The first-order elimination rate constant is the rate constant for the elimination of the drug from the body. The elimination rate constant and the half life are dependent on the total body clearance and the volume of distribution of the drug.
CLT
Vd = k =0.693
t 1/2This rate constant represents drug elimination through all routes of drug elimination such as metabolism, renal excretion, and other routes. The first-order elimination rate constant has units of (time-1).
A semilog graph paper is a graph paper in which the x-axis is a normal linear scale, but the y-axis is a logarithmic scale. Semilog graph paper allows plotting the data at logarithmic intervals without the need for logarithmic transformation.
The y-axis is divided into cycles, each represents 10-fold increase in values (a single log10 unit).