Subcutaneous Injection
A method of drug administration where the compound is injected into the fatty tissue layer beneath the skin. Subcutaneous injection is the most common route for peptide drugs, offering reliable 60-90% bioavailability and suitability for self-administration. Common sites include the abdomen, thigh, and upper arm.
Technical Context
SC injection deposits drug into the subcutis (hypodermis) — the adipose tissue layer between the dermis and muscle fascia, typically 1-2.5cm deep. Absorption occurs primarily via blood capillaries and lymphatic vessels. Absorption rate depends on local blood flow (increased by warming/massage, decreased by cold/vasoconstriction), injection volume, and drug formulation. SC bioavailability for peptides is typically 60-90% with Tmax of 1-8 hours. Recommended sites: abdomen (fastest absorption), anterior thigh, upper outer arm. For self-administered peptide drugs, 4-6mm needles at 90° or 8mm at 45° are typical. Modern pen devices (FlexPen, FlexTouch for semaglutide; Trulicity pen for dulaglutide) use 29-32 gauge needles and semi-automated injection to minimise pain and technique errors.