Insulin

MECHANISM OF ACTION

Insulin lowers blood glucose by facilitating the uptake of glucose into insulin-sensitive tissues, primarily skeletal muscle and adipose tissue, and by inhibiting hepatic glucose production. It binds to the insulin receptor, activating intracellular signaling pathways that promote glucose transporter (GLUT4) translocation to the cell membrane, allowing glucose entry into cells. Additionally, insulin stimulates glycogen synthesis, lipid storage, and protein synthesis while suppressing gluconeogenesis and lipolysis, collectively maintaining normal blood glucose levels and supporting metabolic homeostasis.

PHARMACOKINETICS

Absorption

Insulin absorption depends on its formulation and route of administration. When administered subcutaneously, which is the most common route, absorption is influenced by factors such as injection site, local blood flow, and insulin type. Rapid-acting insulin is absorbed within 10–30 minutes and peaks at 30–90 minutes, while short-acting insulin peaks at 2–4 hours, intermediate-acting at 4–12 hours, and long-acting formulations provide relatively steady levels over 24 hours.

Distribution

Insulin is widely distributed throughout the body, particularly in insulin-sensitive tissues such as the liver, muscle, and adipose tissue. It has limited plasma protein binding.

Metabolism

Insulin is primarily metabolized in the liver, kidneys, and muscle tissues by enzymatic degradation. Enzymes such as insulinase break it down into inactive metabolites.

Elimination

Insulin is eliminated mainly through metabolic degradation, with the kidneys playing a major role in clearing circulating insulin. Only a negligible amount is excreted unchanged in urine.

PHARMACODYNAMICS

Insulin is a peptide hormone that regulates glucose metabolism. It lowers blood glucose levels by facilitating the uptake of glucose into cells, especially in muscle and adipose tissue, and by inhibiting hepatic glucose production. 

ADMINISTRATION

Insulin is usually administered via subcutaneous injection, though intravenous administration may be used in emergencies such as diabetic ketoacidosis. It is available in various formulations, including rapid-acting, short-acting, intermediate-acting, and long-acting types. 

DOSAGE AND STRENGTH

Insulin dosage is individualized based on blood glucose monitoring. It is typically measured in units rather than milligrams. Requirements vary depending on age, weight, type of diabetes, and lifestyle.

DRUG INTERACTIONS

Insulin may interact with several drugs. Some medications (e.g., corticosteroids, diuretics) may increase blood glucose levels, while others (e.g., oral antidiabetic drugs) may enhance the glucose-lowering effect of insulin, increasing the risk of hypoglycemia.

FOOD INTERACTIONS

Food intake significantly affects insulin action. Timing of meals must be coordinated with insulin administration to prevent hypoglycemia or hyperglycemia. Carbohydrate intake plays a key role in determining insulin requirements.

CONTRAINDICATIONS

Insulin is contraindicated in patients with hypoglycemia or hypersensitivity to insulin or its components.

SIDE EFFECTS

• Hypoglycemia (most common) 

• Weight gain 

• Injection site reactions 

• Lipodystrophy (with repeated injections at the same site)

OVER DOSAGE

Overdosage of insulin results in hypoglycemia (low blood glucose levels), which is the most common and potentially dangerous complication. It may occur due to excessive insulin administration, missed meals, increased physical activity, or alcohol consumption.

TOXICITY

The major toxicity of insulin is hypoglycemia, which can range from mild symptoms (sweating, tremors, confusion) to severe complications such as seizures, unconsciousness, and coma. Prompt recognition and treatment with glucose are essential.