How does montelukast (Singulair), a leukotriene blocker, work in the treatment of asthma?

Choice A reason: This is not the preferred agent for the initial treatment of heart failure. Vasodilators are a class of medications that lower the blood pressure by relaxing the blood vessels and reducing the resistance to blood flow. They can be used to treat hypertension, angina, and heart failure, but they are usually added to other medications, such as diuretics or beta blockers, to improve the symptoms and outcomes.

Choice B reason: This is the preferred agent for the initial treatment of heart failure. Diuretics are a class of medications that increase the urine output and reduce the fluid retention in the body. They can be used to treat hypertension, edema, and heart failure, as they reduce the preload and afterload on the heart, and decrease the pulmonary congestion and peripheral edema.

Choice C reason: This is not the preferred agent for the initial treatment of heart failure. Calcium channel blockers are a class of medications that lower the blood pressure and heart rate by blocking the calcium channels in the heart and blood vessels, which cause vasodilation and reduced cardiac contractility. They can be used to treat hypertension, angina, and arrhythmias, but they are not recommended for most patients with heart failure, as they may worsen the cardiac function and increase the mortality.

Choice D reason: This is not the preferred agent for the initial treatment of heart failure. Direct renin inhibitors are a class of medications that lower the blood pressure by inhibiting the enzyme renin, which initiates the renin-angiotensin-aldosterone system, a hormonal pathway that regulates the blood pressure and fluid balance. They can be used to treat hypertension, but they have not been proven to be effective or safe for patients with heart failure.

Choice A reason: ACE inhibitors do not lower heart rate. They lower blood pressure by blocking the conversion of angiotensin I to angiotensin II, which is a potent vasoconstrictor. Beta blockers are the drugs that lower heart rate and blood pressure.

Choice B reason: ACE inhibitors inhibit vasoconstriction. This is the correct statement that describes the action of these medications. By blocking the angiotensin II formation, they prevent the narrowing of the blood vessels and reduce the resistance to blood flow.

Choice C reason: ACE inhibitors do not increase aldosterone secretion. They decrease it. Aldosterone is a hormone that causes the kidneys to retain sodium and water, which increases blood volume and pressure. By blocking the angiotensin II formation, ACE inhibitors reduce the stimulation of aldosterone secretion and promote sodium and water excretion.

Choice D reason: ACE inhibitors do not promote sodium retention. They promote sodium excretion. As explained above, ACE inhibitors reduce the aldosterone secretion and prevent the kidneys from reabsorbing sodium and water. This lowers the blood volume and pressure.