**Question:** Propranolol is contraindicated in diabetes mellitus because it

A. causes hypoglycemia
B. impairs glycemic control
C. increases cardiovascular morbidity
D. does not affect glycemic control

**Correct Answer:** B. impairs glycemic control

**Core Concept:** Propranolol is a beta-blocker, which is a class of medications used primarily for heart conditions like hypertension, angina pectoris, and arrhythmias. However, it can also have some impact on glycemic control in patients with diabetes mellitus.

**Why the Correct Answer is Right:** Propranolol can cause a decrease in insulin secretion and a reduction in peripheral sensitivity to insulin in patients with diabetes mellitus. This results in impaired glycemic control, leading to increased risk of hypoglycemia and exacerbation of the underlying diabetes condition.

**Why Each Wrong Option is Incorrect:**

A. Causes hypoglycemia: While propranolol can lower blood sugar levels, it is not the primary reason for the medication's contraindication in diabetes mellitus. The primary concern is the effect on glycemic control.

B. Impairs glycemic control: As explained, propranolol affects insulin secretion and insulin sensitivity, resulting in worsened glycemic control in diabetic patients, which is the primary concern in this context.

C. Increases cardiovascular morbidity: While propranolol has cardiovascular benefits, the impact on glycemic control outweighs this potential benefit in diabetic patients.

D. Does not affect glycemic control: This statement contradicts the correct answer, as propranolol does have an impact on glycemic control, due to its effects on insulin secretion and insulin sensitivity.

**Clinical Pearl:** In patients with diabetes mellitus, it is crucial to consider the potential effects of medications on glycemic control before administering them. Adequate glycemic control is essential to prevent complications in these patients. If you are unsure about a medication's impact on glycemic control, consult with a medical professional or refer to reliable sources for information.