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Mean arterial pressure = Cardiac output × Peripheral resistance

The preceding equation is a familiar one from physiology. According to this equation, a decrease in either cardiac output or peripheral resistance will decrease blood pressure. Conversely, if high blood pressure is present, something must have increased one of the two variables.

A number of factors will increase cardiac output, including increased heart rate, increased contractility, and increased sodium and water retention. Vasoconstriction will increase peripheral resistance. Decreasing one or more of these factors is the goal of antihypertensive therapy.

Diuretics can be used to decrease blood volume. Drugs are available that interfere with the renin-angiotensin system, which is intimately involved in salt and water balance in the body. Finally, drugs can be used to decrease peripheral vascular resistance or cardiac output. This can be done with direct-acting vasodilators or by using agents that block sympathetic nervous system output.

  1. Diuretics

    1. Thiazides

    2. Loop diuretics

    3. Potassium (K+)-sparing diuretics

  2. Drugs that interfere with the renin-angiotensin system

    1. ACE inhibitors

    2. Angiotensin II receptor antagonists

    3. Aldosterone antagonists

    4. Direct renin inhibitor

  3. Drugs that decrease peripheral vascular resistance or cardiac output

    1. Direct vasodilators

      1. Calcium channel blockers

      2. Nitrates

    2. Sympathetic nervous system depressants

      1. α- and β-Blockers

      2. Clonidine

As you can see from this outline, it is easiest to organize the antihypertensive drugs by their mechanism of action. Some of these drugs are also useful in the treatment of angina or heart failure.


Drugs that increase urine flow are called diuretics. Diuretics play an important role in the management of high blood pressure. They are often used in combination with other classes of antihypertensive drugs. These drugs are ion transport inhibitors in the kidney, so a short review of renal physiology may be useful for you at this point.

There are basically three groups of diuretics, named according to their structure and mechanism of action: thiazide diuretics, loop diuretics, and potassium-sparing diuretics. Consider the group names for these drugs; in particular, the phrase potassium sparing. This tells you that the other two groups cause a loss of potassium. You now know a major side effect of both the thiazide diuretics and the loop diuretics. Next, consider the name loop diuretics. If you have to guess the site of action of these drugs, what would you guess? I am sure you said the loop of Henle. So you see, you already know the site of action of this group.

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Thiazide Diuretics Loop Diuretics Potassium-Sparing Diuretics
HYDROCHLOROTHIAZIDE bumetanide amiloride
chlorthalidone ethacrynic acid triamterene
metolazone torsemide eplerenone

Name recognition is extremely important with these drugs. Many students have missed an exam (or board) question because he or she didn’t recognize a drug ...

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