What happens to insulin
in the body?
1. Intravenous administration invariably results in a quick absorption and distribution of the insulin. Upon injection,it gives instantaneous peak with rapid decline. the plasma half-time of insulin is about 10-12 minutes, so most of the insulin bolus will have dissipated one hour after bolus injection.This mode of administration are recommended only for regular acting and short acting insulin but not for long acting insulin. It is used in acute condition such as diabetes ketoacidosis and perioperative period.
2. Intramuscular injection shows rapid action compared to subcutaneous injection because of the high muscle vascularity. This route is preferable in an extreme dehydration situation like hyperosmolar coma and diabetic ketoacidosis compared to subcutaneous. This is because dehydration results in reduces skin blood flow.
3. Subcutaneous injection is the common mode because this can be performed relatively safely and easily by patients themselves. It is also intended for long term regular use and rate of absorption may be different for each site of injection. For example , insulin injected at arm and abdomen shows rapid action compare to thigh and buttock.
4. Inhalation has been intended for short-acting insulins because of the rich vasculature of the lungs. However, for various reasons such as safety, commercial and inviability the only registered pulmonary insulin named ExuberaR was taken from the market in 2007.
5. Nasal and oral modes of administration are still being explored but have not yet shown any convincing results.
Absorption - Mode of administration can effect the plasma level of insulin
Distribution
Circulating insulin is distributed in equilibrium between free insulin and insulin bound to IgG antibodies The presence of insulin antibodies can delay the onset of insulin activity, reduce the peak concentration of free insulin, and prolong the biologic half-life of insulin
Metabolism
Human insulin is degraded by insulin protease or insulin-degrading enzymes and possibly protein disulfide isomerase. Metabolites formed are inactive.
Elimination
The kidneys and liver responsible for the majority of insulin degradation. About ~60% of the insulin release by the pancreas is degrades by the liver as it is delivered through portal vein blood flow while ~35-45% degrades by the kidney. But for exogenous insulin, since it is no longer delivered directly to the portal vein, kidney plays a major roles in degradating it. For subcutaneous administration, ~60% of the insulin degrades by the kidney and ~30-40% degrades by the liver. Renal failures will effects the clearance of both endogenous insulin (secreted by pancreas or stimulates by oral agent) and exogenous insulin. This will prolong insulin's effect.
Insulin undergo four major process in the body
Diabetic Ketoacidosis is often the first sign of type 1 diabetes in people who do not yet have other symptoms.Fats is broken down for energy and produces ketone bodies as wastes.
Hyperosmolar coma is a severe loss of body water that can lead to shock, coma, and death. It occurs more in people with type 2 diabetes as opposed to type 1 diabetes.