Administration of subcutaneous (s.c.) insulin poses potential problems for a patient who is acutely ill and unable to take oral glucose. The insulin will exert a hypoglycemic effect for several hours, but the rate of absorption is unpredictable in people who are shocked and have peripheral vasoconstriction. Intravenous (i.v.) insulin, by contrast, has a short half-life (2.5 min) and has to be given as a continuous infusion. This works immediately and its effects can be stopped by discontinuing the infusion; dose adjustments have an immediate effect. Insulin delivery by the i.v. route has several indications (Table 6.1), but it is often overprescribed—non-fasting patients are frequently and unnecessarily given i.v. insulin to control hyperglycemia in the absence of ketosis or hyperosmolality. In these situations, s.c. insulin or oral antidiabetic medications should be used.