After a single iv dose the amount of the drug in the body decreases with time.
The rate of drug elimination decreases with time due to the decrease in drug amount in the body.
A plot of the drug excretion rate vs. time is linear on a
and is parallel to the amount vs. time profile.The rate of drug excretion at any time divided by the corresponding plasma concentration is constant, and is equal to the
.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).
The total body clearance is the volume of the plasma or blood which is completely cleared from the drug per unit time. It has units of volume/time.
The CLT for a drug is constant within a patient (dose and concentration independent) when the elimination processes follow first-order kinetics.
The total body clearance is a measure of the efficiency of all eliminating organs in eliminating the drug and it is the sum of all organ clearances (i.e. CLT is the sum of the renal clearance, hepatic clearance and all other organ clearances).
The elimination rate constant and the half life (the dependent pharmacokinetic parameters) are dependent on (is determined from) the total body clearance and the volume of distribution (the independent pharmacokinetic parameters).
CLT
Vd = k andCLT
Vd =0.693
t 1/2