Question

Can the concept of "steady state" be applied similarly on drugs that follow first order and zero order kinetics?

Answer 1

The concept of "steady state "can be applied on drugs that follow first order kinetics.It cannot be applied to drugs which follow zero order kinetics.Steady state refers to the situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination.In other words it is the time during which the concentration remains stable or consistent when the drug is given repeatedly or continuously.For most drugs, the time to reach steady state is four to five half lifes if the drug is given at regular intervals.Medications with short half-lives reach steady state relatively quickly.

In first order kinetics constant proportion of drug is eliminated per unit time where as in zero kinetics constant amount of drug is eliminated per unit time.In clinical pharmacology first order kinetics are considered as linear process because the rate of elimination is propotional to drug concentration.This means that the higher the drug concentration,the higher its elimination rate.The elimination process are not saturated.In zero order kinetics elimination process is saturated.Elimination rate is not propotional to the drug concentration ,but decreasing at higher concentrations.Zero order kinetics are also called non linear kinetics.

So the concept of steady state cannot be applied to zero kinetic drugs safely.