A 50-year-old male with a history of type 2 diabetes is prescribed sitagliptin. Sitagliptin works by:

Correct Answer: C

Rationale: Rationale: 1. Sitagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor. 2. DPP-4 enzyme breaks down incretin hormones like GLP-1. 3. By inhibiting DPP-4, sitagliptin increases incretin hormone levels. 4. Incretin hormones stimulate insulin release and inhibit glucagon. 5. Thus, sitagliptin indirectly increases insulin secretion. Summary: A: Incorrect - Sitagliptin indirectly increases insulin secretion. B: Incorrect - Sitagliptin does not affect glucose absorption. D: Incorrect - Sitagliptin does not increase renal glucose excretion.

Correct Answer: B

Rationale: The correct answer is B: Beta-adrenergic receptors. Albuterol is a beta-2 adrenergic agonist that works by binding to beta-2 adrenergic receptors in the airway smooth muscle, leading to bronchodilation. This mechanism helps in treating conditions like asthma and COPD. Choice A (Alpha-adrenergic receptors) is incorrect because albuterol specifically targets beta-adrenergic receptors, not alpha-adrenergic receptors. Choice C (Cholinergic receptors) is incorrect because albuterol does not directly interact with cholinergic receptors. Choice D (Dopaminergic receptors) is incorrect as albuterol does not have a significant affinity for dopaminergic receptors. In conclusion, the correct answer is B because albuterol's mechanism of action involves activating beta-adrenergic receptors to produce bronchodilation.

Correct Answer: B

Rationale: The correct answer is B: Inhibiting HMG-CoA reductase. Simvastatin is a statin medication that works by inhibiting the enzyme HMG-CoA reductase, which is involved in the synthesis of cholesterol in the liver. By inhibiting this enzyme, simvastatin reduces the production of cholesterol in the body, leading to lower LDL cholesterol levels. Choice A is incorrect because simvastatin actually decreases LDL cholesterol levels. Choice C is incorrect as blocking cholesterol absorption in the intestine is the mechanism of action for a different class of drugs called bile acid sequestrants. Choice D is incorrect as simvastatin primarily reduces LDL cholesterol levels and has a modest effect on increasing HDL cholesterol levels.

Correct Answer: B

Rationale: Step-by-step rationale for choice B: 1. Spironolactone is a mineralocorticoid receptor antagonist. 2. It blocks aldosterone receptors in the kidneys. 3. Aldosterone is a hormone that promotes sodium and water retention, leading to increased blood volume and pressure. 4. By blocking aldosterone receptors, spironolactone reduces sodium and water retention, helping to decrease blood volume and pressure in heart failure patients. Summary of why other choices are incorrect: A: Inhibiting sodium reabsorption in the kidneys is the mechanism of action of loop diuretics, not spironolactone. C: Spironolactone actually increases potassium retention, not excretion. D: Increasing cardiac contractility is the mechanism of action of positive inotropic agents, not spironolactone.

Correct Answer: B

Rationale: The correct answer is B: Amlodipine. It is a calcium channel blocker commonly prescribed for hypertension by inhibiting calcium influx into heart and blood vessel cells, leading to vasodilation and decreased blood pressure. Lisinopril (A) is an ACE inhibitor, Losartan (C) is an ARB, and Hydrochlorothiazide (D) is a thiazide diuretic, all of which work through different mechanisms to lower blood pressure.