Nasal drug absorption specific applications

Medicinal products administered at a specific site to obtain a local effect should preferably not be absorbed systemically. However, significant amounts of active substance can be absorbed, e.g. after application on the skin. Removal of locally acting active substances from the site of action by systemic absorption may result in systemic effects that can be considered as adverse effects. After nasal, ocular, pulmonary and rectal administration of active substances for a local effect, absorption into the systemic circulation is likely to occur. This may cause adverse effects and limit the duration of the desired drug effect. Conversely it should be realised that the systemic route is often also the main route for clearance of the active substance from the site of administration. The bioavaUability of locally acting medicines is, of course, not determined by the amount of active substance that reaches the systemic circulation. As an alternative the fraction of the active substance that is dissolved in the aqueous fluids at the site of application is usually taken as a measure for the bioavailability. 

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