Which method involves injecting a drug under the skin, useful for protein products?

The correct method for injecting a drug under the skin, particularly for protein products, is subcutaneous injection. This method involves delivering the medication into the layer of fat and connective tissue just beneath the skin. This route is often preferred for protein-based drugs, including insulin and certain vaccines, due to its ability to provide a slow and sustained absorption into the bloodstream, which is beneficial for long-acting effects.

Subcutaneous injections have several advantages, such as being relatively easy to perform and causing minimal discomfort when compared to other injection methods. The subcutaneous tissue has a good blood supply, allowing for effective absorption of the medication, which is especially important for protein drugs that may be broken down by digestive processes if given orally.

In contrast, intramuscular injections deliver the medication deeper into the muscle tissue, offering faster absorption but often at the expense of discomfort and a more invasive technique. Intravenous injections provide immediate access to the bloodstream but require more technical skill and equipment. Inhalation is a different delivery method primarily used for respiratory conditions and would not apply to injectable forms administered under the skin.