isophane

Isophane refers to a form of insulin commonly known as insulin isophane or neutral protamine Hagedorn (NPH) insulin. It is an intermediate-acting insulin preparation created by combining insulin with protamine, and sometimes zinc, to form an insoluble complex. When injected subcutaneously, the complex dissolves slowly, delaying absorption and producing a longer duration of action than rapid-acting insulin.

Pharmacokinetics vary, but typical onset occurs within 1 to 3 hours, with a peak effect in roughly 4 to 12 hours, and a duration of action up to 18 to 24 hours. This profile makes isophane insulin useful for providing basal insulin coverage, often administered once or twice daily, and it is frequently used in combination with a short-acting insulin in mixed regimens for both type 1 and type 2 diabetes.

Historically, the preparation is associated with the name Neutral Protamine Hagedorn, after the researchers who developed it. The term “isophane” is an older descriptor for this type of complex. In clinical practice, NPH insulin remains a widely used intermediate-acting option, though newer long-acting basal insulins have supplemented or replaced it in some regimens.

Adverse effects are similar to other insulin products and include the risk of hypoglycemia and local injection-site reactions. Dosing requires individual adjustment and careful monitoring, particularly during changes in diet, activity, illness, or when starting or stopping other antidiabetic therapies.