Suppose a pet gets an insulin shot every 12 hours, gets 15 hours duration from each shot, and is on an insulin that has a three hour onset. During the 3 hours after each insulin shot, there will be two insulin shots working to reduce blood glucose levels: the diminishing previous shot and the rising current shot. This may mean that the ongoing insulin dose should be less than if no overlap was used.
Using overlap safely and effectively requires significant information about and analysis of how a particular insulin works in your pet (its duration, onset, and peak) and how feeding and other forces (such as exercise or sleep) affect your pets' blood glucose levels. Using overlap may result in diminished insulin needs as your pet's blood glucose levels are reduced from the diminishing effect of the previous shot, and possibly also from the carryover effects of previous shots.
Also see insulin stacking.
Overlap is not the same as carryover.
- Causes of Hyperglycemia and Hypoglycemia in diabetic dogs Greco, Deborah, 2009, DVM 360