Structural Biochemistry/Subcutaneous

Definition
A subcutaneous injection (SC, SQ, SubQ) is a method of drug administration in which the drug is injected into hypodermis, the fatty tissue layer directly beneath the dermis and epidermis. Because there is limited blood flow to the hypodermis, subcutaneous injection is usually used when slow absorption of medication is preferred. Drugs that are administered using this method must be soluble and potent in small concentrations. Common medications used with this procedure include heparin, insulin, growth hormones, and vaccines against MMR and varicella.

Sites and Method of Injection
With subcutaneous injection, the drug is usually administered through loose interstitial tissues of the upper arm, the anterior surface of the thigh, the lower portion of the abdomen, or the lower back. When injecting, the skin is pinched up to prevent injection into muscle. It is recommended to use the same site for routine injections. The shot is given at a straight 90 degree angle if at least 2 inches of skin can be grasped. Otherwise, it is given at a 45 degree angle.

Absorption Rate
Factors that may increase absorption rate are heat, massaging, co-administers vasodilators, or hyaluronidase at the site of injection. Epinephrine may decrease the absorption rate due to decreased blood flow.