What type of drug administration involves injecting into the fatty layer just under the skin?

Subcutaneous drug administration involves injecting medication into the fatty layer just beneath the skin. This method allows for the medication to be absorbed slowly into the bloodstream, which can be beneficial for certain types of medications that require a gradual release. Common examples include insulin or vaccines, which can be effectively delivered in this manner.

Intravenous administration involves injecting the medication directly into the bloodstream via a vein, leading to rapid effects. Intramuscular administration entails injecting into a muscle, where absorption can be faster than subcutaneous but still slower than intravenous. Transdermal delivery involves applying drugs to the skin in the form of patches for absorption through the skin, bypassing injection entirely. Hence, the option focused on subcutaneous delivery aligns precisely with the described method of administration.