## **Core Concept**
The plasma half-life of a substance is the time it takes for its concentration in the blood to reduce by half. For insulin, understanding its half-life is crucial for managing diabetes mellitus, as it directly affects how long the glucose-lowering effect lasts.

## **Why the Correct Answer is Right**
The correct half-life of insulin in plasma is approximately **6 minutes**. Insulin is rapidly cleared from the circulation by the liver and kidneys. This short half-life necessitates continuous or repeated administration for individuals with diabetes who require insulin therapy. The liver's role in insulin clearance involves receptor-mediated endocytosis, while the kidneys filter insulin, which is then reabsorbed and degraded.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately reflect the known half-life of insulin.
- **Option B:** Similarly, this option does not match the established pharmacokinetic profile of insulin.
- **Option C:** This option suggests a much longer half-life than what is observed for insulin, which does not align with its rapid clearance from plasma.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that despite insulin's short half-life in plasma, its biological effects on glucose metabolism can last much longer. This discrepancy is due to the complex interactions of insulin with various tissues and its impact on glucose uptake and storage. For clinical purposes, the duration of action of insulin preparations is more relevant than the plasma half-life of native insulin.

## **Correct Answer:** . 6 minutes