Injection site rotation (revision 7)

Injection site rotation is the practice of varying the location of successive subcutaneous injections. Its purpose is to avoid the local tissue changes that repeated injection at one point produces, principally lipohypertrophy — a thickening of the subcutaneous tissue from which absorption becomes erratic.^[1]

The evidence base is largely from insulin therapy, where lipohypertrophy is common, is associated with unpredictable glycaemic control, and resolves slowly when the affected area is rested. Its relevance to weekly peptide administration is less well characterised, since injection frequency is roughly one seventh of that in basal-bolus insulin therapy.^[2]

Two rotation patterns are distinguished. Rotating within a region — moving a couple of centimetres each time while staying in the same anatomical area — preserves that region's absorption characteristics. Rotating between regions changes them as well.^[1]

Lipohypertrophy is a local proliferation of subcutaneous adipose tissue at sites of repeated injection. It presents as a soft or rubbery thickening, often more readily felt than seen, and is frequently painless — which is part of why it is under-recognised.^[2]

Absorption from affected tissue is reduced and more variable. In insulin therapy this produces unexplained variability that persists until the affected area is rested, and continued injection into it is self-reinforcing because reduced sensation makes the site attractive.

Whether repeated weekly injection of a peptide produces the same lesion is not established. Frequency is much lower, but the mechanical and pharmacological insults are qualitatively similar, and the literature on this specific question is thin.^[3]