Subcutaneous Injection
Definition
A method of drug administration involving injection into the subcutaneous tissue, the fatty layer located between the skin and the underlying muscle, allowing for slow and sustained absorption into the bloodstream.
Subcutaneous Injection
A subcutaneous injection delivers medication into the layer of fatty tissue (adipose tissue) situated just beneath the skin and above the muscle. This route of administration is widely used for biologics, peptides, and proteins that cannot survive oral administration due to degradation in the gastrointestinal tract. The subcutaneous space provides a depot effect, enabling the drug to be absorbed slowly and steadily into the bloodstream through surrounding capillaries. Common injection sites include the abdomen, thigh, and upper arm, and patients can typically be trained to self-administer subcutaneous injections at home.
For incretin-based therapies including retatrutide, subcutaneous injection is the standard route of administration. Retatrutide is formulated for once-weekly subcutaneous injection, leveraging the slow absorption from the subcutaneous depot combined with the peptide’s engineered long half-life to maintain therapeutic drug levels throughout the dosing interval. In clinical trials, participants self-administered retatrutide via prefilled syringes or autoinjectors, and injection site reactions were generally mild and infrequent.
The subcutaneous route offers several practical advantages over intravenous administration: it does not require a healthcare professional for each dose, it allows for flexible dosing schedules compatible with patients’ daily routines, and it avoids the peak-and-trough drug level fluctuations associated with bolus intravenous dosing. These characteristics make once-weekly subcutaneous injection a patient-friendly approach that supports long-term adherence, which is essential for chronic conditions like type 2 diabetes and obesity where treatment duration may extend indefinitely.