What is the absorption rate of a subcutaneous injection?

The absorption rate of a subcutaneous injection is best characterized as moderate through fat tissue. When a drug is injected subcutaneously, it is delivered into the fatty layer beneath the skin rather than directly into muscle tissue or bloodstream. This fat tissue has a different vascular supply compared to muscle, which affects how quickly the medication is absorbed into the bloodstream.

Typically, absorption from the subcutaneous layer is slower than intramuscular injections because the subcutaneous tissue has fewer blood vessels than muscle. While capillaries are present for absorption, the rate through capillaries in this context isn’t described as "fast" since it is moderated by the fatty tissue surrounding the injection site.

The absorption can also be variable based on several factors, including blood flow to the area and the nature of the drug being administered. For example, medications that are hydrophilic might be absorbed at different rates compared to lipophilic medications, reflecting this variability.

In summary, while the absorption from the subcutaneous tissue does involve capillary action, characterizing it specifically by stating it's "fast" overlooks the influence of the surrounding fatty tissue and overall absorption dynamics. Thus, the best description of the absorption rate of a subcutaneous injection is moderate through fat tissue.