The lung is the major organ of excretion for gaseous and volatile substances.
The breathalyzer test is based on a quantitative pulmonary excretion of
ethanol. Most of the gaseous anesthetics are extensively eliminated in expired
This is not really a method of drug excretion as the drug will usually be
swallowed and reabsorbed, thus a form of 'salivary recycling'. Drug excretion
into saliva appears to be dependent on pH partition and protein binding. This
mechanism appears attractive in terms of drug monitoring, that is determining
drug concentration to assist in drug dosage adjustment. For some drugs, the
saliva/free plasma ratio is fairly constant. Therefore drug concentrations in
saliva could be a good indication of drug concentration in plasma. For some
drugs localized side effects maybe due to salivary excretion of the drug.