Hypertension, or high blood pressure, is a condition in which the blood exerts too much pressure on the walls of vessels as it flows through the body. If high blood pressure remains untreated, it can damage blood vessels in the kidneys, heart and brain. This increases your risk of developing heart disease, heart failure, kidney failure and stroke. There are several medications that effectively treat hypertension, with each high blood pressure medication working in different ways.
Diuretics
Diuretics, or water pills, work in the kidneys to reduce the amount of fluid in the blood. This reduces the pressure on the blood vessels. Some common diuretics include furosemide and hydrocholorthiazide.
Calcium Channel Blockers
Calcium is an essential element in smooth muscle contraction. Calcium channels located on the walls of muscle cells control the entrance of calcium into the cell. Calcium channel blockers reduce the influx of calcium into the muscle cell, which reduces the ability of the muscle cell to contract. This helps relax the layer of smooth muscle that lines the blood vessels. Calcium channel blockers include drugs such as diltiazem, verapamil and amlodipine.
ACE Inhibitors
ACE Inhibitors, or angiotensin-converting enzyme inhibitors, were the first class of drugs developed that acted on the renin-antiotensin system, a series of enzymes released by the kidneys to regulate blood pressure. In healthy individuals, low blood pressure or low sodium in the blood flowing to the kidneys stimulates the release of the enzyme renin. This sets off a cascade of reactions that increase blood pressure. In some cases, hypertension is a direct result of high renin levels in the plasma. Even people with normal renin levels, however, experience a reduction in blood pressure after taking drugs that inhibit the renin-angiotensin sysystem.
ACE inhibitors block one of the enzymes responsible for converting antiotensin I to angiotensin II. ACE inhibitors also slow the breakdown of bradykinin, a substance that dilates blood vessels. In some patients, the increased amount of bradykinin causes a chronic cough. This cough causes many people to stop taking ACE inhibitors.
Some examples of ACE inhibitors are captopril, benazepril and lisinopril.
Angiotensin Receptor Blockers
Angiotensin II has two main functions in the body: It constricts blood vessels and stimulates the release of the hormone aldosterone from the adrenal glands. Aldosterone increases the amount of sodium and water retained by the body, which increases blood pressure.
Angiotensin receptor blocking agents, also known as ARBs, decrease blood pressure by blocking the affect of angiotensin II in the body. Since they block the action of angiotensin II, rather than slowing down its production, they are a more complete inhibitor of angiotensin II. Valsartan and losartan are two popular ARBs.
Renin Inhibitors
Renin is the first enzyme in the renin-angiotensin system. Renin breaks angiotensinogen down to angiotensin I. Renin inhibitors lower blood pressure by blocking the action of renin. Aliskiren is a renin inhibitor.
Beta Blockers
Beta blockers blunt the effect of adrenaline in the central nervous system. Although adrenaline is most famously known for the "fight or flight" response to stressful situations, it is constantly secreted by your nervous system. Beta blockers reduce the effect of adrenaline on the blood vessels and heart to reduce blood pressure and slow heart rate. They may also have some effect on the renin-angiotensin system in the kidneys. Beta blockers include the drugs propranolol, atenolol and metoprolol.
Alpha Blockers
Alpha blockers block another type of adrenaline receptor in the body. Alpha blockers dilate blood vessels and reduce blood pressure, but have less effect on heart rate. Alpha blockers are powerful vasodilators and can sometimes reduce blood pressure so drastically that fainting or dizziness occurs. Examples of alpha blockers are prazosin and terazosin.
Alpha-2 Agonists
Alpha-2 agonists stimulate the alpha-2 receptors in the brain. Stimulation of these receptors causes the blood vessels to dilate, or relax. Stopping an alpha-2 agonist suddenly can cause a dangerous spike in blood pressure, so patients should be careful to take them exactly as directed. Methyldopa, guanfacine and clonidine are drugs in this class.
References
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
- U.S. Pharmacist magazine: Treatment of Hypertension in the Elderly
