In what situations might a medication need to be administered subcutaneously?

Subcutaneous administration is particularly suitable for medications that require slow and consistent absorption over time. Insulin, used in the management of diabetes, and heparin, an anticoagulant, both benefit from this method, as it allows for sustained therapeutic effects without causing rapid fluctuations in drug levels. The subcutaneous tissue has a rich blood supply, promoting the gradual release of the medication into the bloodstream, making it ideal for maintaining stable drug levels.

Rapid absorption, as seen with morphine, typically necessitates a different route of administration, such as intravenous, to achieve immediate effects. Oral medications that require quick effects would also not be suitable for subcutaneous delivery, as this route does not provide that level of immediacy. Topical medications that are designed for local effect are better applied directly to the skin rather than through subcutaneous injection, as they are meant to work at the site of application rather than being absorbed systemically. Thus, the choice of subcutaneous administration aligns perfectly with the need for a slower, more sustained absorption profile that is characteristic of medications like insulin and heparin.