Last month we talked about high blood pressure (hypertension) — definitions, prevalence, and how it’s dubbed “the silent killer” because it usually doesn’t cause any symptoms. We mentioned that sometimes a change in lifestyle (e.g. diet and exercise) might be all it takes to regain normal blood pressure. However, for many people it takes more than that, and it’s usually an antihypertensive medication. Fortunately there are many medications to choose from, and many are inexpensive with few side effects.
The blood pressure is determined by several factors, but the most important is the tone of the arteries — how tense or relaxed they are. The more relaxed the artery, the lower the blood pressure. The “hardness” or rigidity of the vessels also affects the blood pressure, especially the top number (systolic). Antihypertensives are usually divided into about 7 major groups according to the mechanism by which they relax arteries and thus lower the pressure. (Detailed description of the mechanisms of action of these medications is beyond the scope of this article.) Let’s talk about 6 of these now.
Diuretics (known as “water pills”) are the mainstay of antihypertensive therapy, and are often one of the first medications started. This drug class is very complicated and diuretics are used for more than one medical condition. In general, however, they work by reducing the total amount of fluid in our circulation, thus reducing the pressure in the system. Some common diuretics include hydrochlorothiazide, spironolactone, and furosemide (Lasix). Some of these can cause dangerous potassium loss or accumulation, so don’t be surprised if your primary care provider (PCP) recommends testing your potassium after starting this medication. If an excessive dose is taken over time, a patient can become dehydrated. Thus your PCP will have a plan to follow your labs and clinical response carefully after starting diuretics.
Another large group of commonly used antihypertensives are the ACE-inhibitors (ACE-1) and the ARBs (ACE-2). Both of these groups act by blocking the production of a chemical that increases the tone of the arteries. The ACE-1 inhibitors (e.g. enalopril, lisinopril, captopril) are very effective in lowering blood pressure, and they are often combined with one of the diuretics above. The ACE-1 inhibitors, especially enalapril (Vasotec) quickly became known to cause a nagging, dry cough in a few people. The ARBs (e.g. losartan, valsartan) are similar in their effects to the ACE-1 inhibitors, but they are much less likely to have the cough side effect.
The tone of the arteries is controlled in part by the central (brain) and peripheral (nerves) nervous systems. Centrally-acting antihypertensives (e.g. clonidine) act by directly interacting in the brain to limit signals traveling to the peripheral nerves that control the tone of the arteries. These can be very effective, but since they act directly in the brain, there can be side effects that may or may not be unwanted (e.g. sleepiness).
Beta-blockers (e.g. atenolol, metoprolol, propranolol, carvedilol) also decrease blood pressure, but the mechanism of action is complex and involves various degrees of slowing the heart and decreasing the strength of its contractions, central effects (as above), and interactions with receptors on the arteries to decrease their tone. Other direct effects on the arteries are also probably involved. Beta-blockers are often used to lower blood pressure and have other beneficial effects in people who have suffered a heart attack. Although beta-blockers usually have few practical side-effects, care must be taken in diabetic patients and those with chronic obstructive pulmonary disease (COPD).
Alpha-blockers (e.g. prazosin, terazosin) act directly on alpha receptors on the arteries to block the effects of circulating adrenaline that increases tension, thus relaxing the arteries. Alpha blockers are sometimes used to decrease the size of the prostate gland in men who are bothered by getting up at night to urinate. Since alpha-blockers decrease the tone of arteries, these medications can reduce the size of the highly vascular prostate gland. These can sometimes have the unwanted side effect of blood pressure dropping suddenly when the patient stands up. Thus patients, especially the elderly, are cautioned to sit first or stand up slowly when arising from bed.
Calcium channel blockers (e.g. nifedipine, Norvasc, amlodipine) relax arteries by blocking calcium entering the arteries, one mechanism by which the arterial wall tension is maintained. In some people, unwanted leg swelling can limit their use.
Strategies — PCPs recommend different medications, or combinations of medications, based on a patient’s individual genetics, medical history, and current conditions. In general, it is better to take two medications, each at a low dose, than to take the maximum dose of a single medication. Higher doses of any medication usually increase the chances of unwanted side effects.
New, brand-name antihypertensives can be expensive. Fortunately there are good representatives of each class above that have gone off-patent, are available generically, and thus often on the “$4 List” at many pharmacies. If yours is very expensive, ask your PCP if there is a generic equivalent that you can take.
What can you do if you’re already taking strong doses of all of the medications above, and your blood pressure is still far above the goal of 120/80? Stay tuned for Part 3 next month!
Dr. Fleming is the Medical Director of The Jane Pauley Community Health Center (part of Community Health Network). Ideas for this column can be e-mailed to Dr. Fleming at AskDrFleming@gmail.com