Types of Antihypertensive Medications
Mechanisms of Different Drugs to Treat High Blood Pressure
Apr 11, 2009
Hypertension, or elevated blood pressure, is one of the most common medical conditions. In most cases, it is a silent risk factor for other conditions, such as a heart attack or stroke. The medical community greatly emphasizes the importance of controlling blood pressure. Many drugs are available to control high blood pressure and work in many ways. The major classes of antihypertensive medications and their mechanisms of action are described as follows.
Diuretics
Diuretics are drugs that increase the amount of urine eliminated from the body. Normally, as blood flows through the kidneys, fluid, electrolytes, and small substances are filtered into the nephrons of the kidney but most of the filtrate is reabsorbed back into the bloodstream. Diuretics work by blocking the reabsorption process so that extra urine is produced.
Depending on the site of action, diuretics are further classified into loop diuretics (e.g., furosemide) that act on the loop of Henle in the nephron, thiazide diuretics (e.g., hydrochlorothiazide) that block reabsorption at the distal tubule of the nephron, and potassium-sparing diuretics (e.g., spironolactone) that function at the collecting ducts in the kidney. Of these three, thiazide diuretics and potassium-sparing diuretics are the ones used for hypertension.
ACE Inhibitors
Certain antihypertensive drugs may target the renin-angiotensin pathway, a set of chemical reactions that ultimately boosts blood pressure when it gets low. Though the process is complicated, the main steps involve the conversion of angiotensin I to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs. ACE inhibitors (e.g., lisinopril), work by blocking ACE, thereby lowering blood pressure.
Angiotensin II Receptor Blockers
Instead of ACE inhibitors, antihypertensive drugs called angiotensin II receptor blockers (e.g., losartan) can lower blood pressure by blocking the receptors for angiotensin II. This class of drugs is considered when a patient is averse or allergic to ACE inhibitors.
Beta Blockers
Beta blockers (e.g., metoprolol) are drugs that decrease the heart's rate and contractility, which in turn lowers blood pressure. These medications are generally used when other conditions requiring beta blockers are present, such as congestive heart failure and myocardial infarction.
Calcium Channel Blockers
Calcium channel blockers (e.g., nifedipine) are medications that inhibit transport of calcium across cell membranes. They primarily act on the smooth muscle layer of arteries, causing relaxation of smooth muscle, increased arterial diameter, and lowered blood pressure. Certain drugs in this class, such as diltiazem, also reduce heart muscle contractility.
Choice of Antihypertensives
The above drugs are prescribed for many cases of hypertension. Doctors choose the appropriate medications by taking into account many factors, such as the patient's comorbid conditions and the side effect profile of the drug. Often, multiple medications are required, and some patients may benefit just as well from combination antihypertensive pills.
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