Which of the following describes typical characteristics of a subcutaneous injection?

• A. High volume (>5 ml), hypertonic, acidic
• B. Low volume (<3 ml), isotonic, physiological pH
• C. Any volume, isotonic, physiological pH
• D. Low volume, isotonic, basic pH

Answer: (B)

Subcutaneous injections work best when the formulation stays gentle to the tissue: a small amount, isosmotic with body fluids, and near the normal pH of blood. The subcutaneous space can only accommodate a limited volume without causing pain or distorting tissue, so keeping the volume low helps ensure predictable absorption. Isotonicity prevents osmotic shifts that would draw water in or out of cells, reducing tissue irritation. A pH close to physiological minimizes local irritation and damage to the injection site. Therefore a low volume (<3 mL), isotonic solution with physiological pH is the typical, best description for subcutaneous injections. Higher volumes, hypertonic solutions, or solutions with acidic or basic pH would increase pain, tissue irritation, or absorption problems.