Which route of administration is indicated by the abbreviation 'sl'?

The abbreviation 'sl' stands for sublingual, which refers to the method of administering medication by placing it beneath the tongue. This route allows for the medication to dissolve and be absorbed directly into the bloodstream through the mucous membranes, leading to a rapid onset of action. Sublingual administration is particularly useful for certain medications that need to bypass the gastrointestinal tract and avoid first-pass metabolism in the liver, thus ensuring that a more significant amount of the active ingredient reaches systemic circulation quickly.

In contrast, the other options represent different routes of administration that do not involve placing a medication under the tongue. Topical administration involves applying a medication directly onto the skin, rectal administration involves inserting medication into the rectum, and inhalation refers to delivering medication through the respiratory tract. Each of these methods has distinct advantages and specific usages, but for the abbreviation 'sl', sublingual is the accurate route.