**Question:** Which one of the following statements about biguanides is not true -

A. Biguanides reduce blood glucose levels by increasing glucose uptake in muscle cells and decreasing hepatic glucose production.
B. Metformin is the only biguanide used in the treatment of type 2 diabetes mellitus.
C. Biguanides cause lactic acidosis as a side effect.
D. Biguanides are effective in weight reduction and improving cardiovascular outcomes.

**Correct Answer: C. Biguanides cause lactic acidosis as a side effect.**

**Core Concept:** Biguanides are a class of medications primarily used in the treatment of type 2 diabetes mellitus. They work by increasing glucose uptake in muscle cells and reducing hepatic glucose production.

**Why the Correct Answer is Right:** Biguanides are generally well-tolerated medications with minimal side effects. Lactic acidosis is a severe and life-threatening side effect associated with metformin, a biguanide drug. This side effect occurs when the acidic lactic acid accumulates in the blood, leading to an imbalance in the body's pH and potentially causing respiratory distress and renal failure.

**Why Each Wrong Option is Incorrect:**

A. The statement about biguanides reducing blood glucose levels and improving glucose uptake is accurate and essential for understanding their mode of action and therapeutic use.

B. While metformin is a widely used biguanide, this statement does not apply to all biguanides. Other biguanides, such as phenformin, were withdrawn from the market due to concerns about lactic acidosis.

D. Biguanides are not primarily known for their weight reduction or cardiovascular benefits. These benefits are associated with metformin, but not all biguanides possess these effects.

**Clinical Pearl:** Although biguanides are generally safe and effective in managing type 2 diabetes, physicians should closely monitor patients for signs and symptoms of lactic acidosis when prescribing metformin, especially in patients with kidney dysfunction or heart failure. Adequate hydration and regular renal function tests are crucial in preventing lactic acidosis.