## Core Concept
Dextrans are a group of **polysaccharides** composed of glucose molecules linked by **α-1,6-glycosidic bonds**. They are produced by certain bacteria and are used in medicine for **plasma volume expansion** and as **anticoagulants**.

## Why the Correct Answer is Right
Dextrans work by increasing **plasma volume**, which helps to maintain blood pressure and perfusion of vital organs. They are commonly used in **surgical settings** and for **treating hypovolemia**. Their mechanism involves drawing fluid into the bloodstream, thereby expanding the **intravascular volume**.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because dextrans do not primarily act as **antibiotics**; they are used for their **hemodynamic effects**.
* **Option B:** This option is incorrect as dextrans are not **mainly metabolized by the liver**; they are primarily **excreted unchanged in the urine**.
* **Option C:** This option might seem plausible but is incorrect because while dextrans can affect **coagulation**, saying they are used "mainly" for this purpose is misleading; their primary use is for **volume expansion**.
* **Option D:** Without the actual text of option D, we proceed with the understanding that the correct answer provided indicates the most accurate statement about dextrans.

## Clinical Pearl / High-Yield Fact
A key point to remember is that dextrans can interfere with **blood typing** and **cross-matching** due to their effect on rouleaux formation of red blood cells. Therefore, **blood samples for typing should be taken before dextran administration**.

## Correct Answer Line
**Correct Answer: D.**