Kinetic processes of elimination for a large number of drugs is:

Large number of drugs follow first order kinetics of elimination i.e. a constant fraction of the drug is eliminated in unit time. Very few drugs e.g. alcohol, have zero order elimination pattern where in a constant amount of the drug is eliminated in unit time. For few other drugs the enzymes participating in the metabolic reactions are saturable hence at higher doses these drugs change their pattern from first order to zero order e.g. theophylline, phenytoin, etc.