Some chemicals (e.g. ethanol) are eliminated by zero order kinetics. How is this different from 1st order
elimination? Is half-life a constant with drugs eliminated by zero order? What causes a drug to be
eliminated by zero order instead of 1st order kinetics? .
Ans )
Chemical elimination or clearance from the body can occur via different kinetics, which can be classified
into two types: first-order and zero-order kinetics.
First-order kinetics describes a process in which the rate of elimination is proportional to the
concentration of the substance being eliminated. This means that as the concentration of the substance
decreases over time, the rate of elimination also decreases proportionally.
A constant fraction of the drug is eliminated per unit of time, resulting in an exponential
decrease in drug concentration. The half-life of a substance eliminated by first-order kinetics is a
constant, meaning that the time it takes for the concentration to decrease by 50% is the same,
regardless of the initial concentration.
Zero-order kinetics describe a process in which the rate of elimination is independent of the
concentration of the substance being eliminated. This means that a constant amount of the drug is
eliminated per unit of time, regardless of the concentration of the drug. This results in a linear decrease
in drug concentration over time. The half-life of a substance eliminated by zero-order kinetics is not
constant but decreases as the drug concentration decreases.
Drugs that are eliminated by zero-order kinetics typically exhibit a saturable elimination mechanism,
meaning that the rate of elimination becomes saturated when the elimination pathways become
saturated with the drug. Ethanol is an example of a drug eliminated by zero-order kinetics, which means
that the rate of elimination is not affected by the concentration of ethanol in the body. In other words, a
constant amount of ethanol is eliminated per unit of time. This is because ethanol is primarily eliminated
by hepatic metabolism, and the enzymes involved in this process have a limited capacity. Therefore, as
the concentration of ethanol in the body increases, the enzymes involved in the metabolism process
become saturated, and the rate of elimination becomes constant.
The half-life of a drug eliminated by zero-order kinetics is not constant, unlike the half-life of a drug
eliminated by first-order kinetics. As the drug concentration decreases, the rate of elimination also
decreases, resulting in a longer half-life. This is because, in zero-order kinetics, the rate of elimination is
dependent on the amount of the drug present in the body, and as the drug concentration decreases, the
rate of elimination decreases proportionally.
Drugs eliminated by zero-order kinetics have a constant rate of elimination, regardless of their
concentration in the body, and their half-life is not constant but decreases with decreasing
concentration. Saturable elimination mechanisms, such as hepatic metabolism, are responsible for the
elimination? Is half-life a constant with drugs eliminated by zero order? What causes a drug to be
eliminated by zero order instead of 1st order kinetics? .
Ans )
Chemical elimination or clearance from the body can occur via different kinetics, which can be classified
into two types: first-order and zero-order kinetics.
First-order kinetics describes a process in which the rate of elimination is proportional to the
concentration of the substance being eliminated. This means that as the concentration of the substance
decreases over time, the rate of elimination also decreases proportionally.
A constant fraction of the drug is eliminated per unit of time, resulting in an exponential
decrease in drug concentration. The half-life of a substance eliminated by first-order kinetics is a
constant, meaning that the time it takes for the concentration to decrease by 50% is the same,
regardless of the initial concentration.
Zero-order kinetics describe a process in which the rate of elimination is independent of the
concentration of the substance being eliminated. This means that a constant amount of the drug is
eliminated per unit of time, regardless of the concentration of the drug. This results in a linear decrease
in drug concentration over time. The half-life of a substance eliminated by zero-order kinetics is not
constant but decreases as the drug concentration decreases.
Drugs that are eliminated by zero-order kinetics typically exhibit a saturable elimination mechanism,
meaning that the rate of elimination becomes saturated when the elimination pathways become
saturated with the drug. Ethanol is an example of a drug eliminated by zero-order kinetics, which means
that the rate of elimination is not affected by the concentration of ethanol in the body. In other words, a
constant amount of ethanol is eliminated per unit of time. This is because ethanol is primarily eliminated
by hepatic metabolism, and the enzymes involved in this process have a limited capacity. Therefore, as
the concentration of ethanol in the body increases, the enzymes involved in the metabolism process
become saturated, and the rate of elimination becomes constant.
The half-life of a drug eliminated by zero-order kinetics is not constant, unlike the half-life of a drug
eliminated by first-order kinetics. As the drug concentration decreases, the rate of elimination also
decreases, resulting in a longer half-life. This is because, in zero-order kinetics, the rate of elimination is
dependent on the amount of the drug present in the body, and as the drug concentration decreases, the
rate of elimination decreases proportionally.
Drugs eliminated by zero-order kinetics have a constant rate of elimination, regardless of their
concentration in the body, and their half-life is not constant but decreases with decreasing
concentration. Saturable elimination mechanisms, such as hepatic metabolism, are responsible for the
