Diuretic drugs help the kidneys excrete more sodium in the urine. The sodium, because it associates with water, takes excess water with it. The reduction in the amount of fluid flowing through the blood vessels reduces pressure on the blood vessel walls. Doctors will probably suggest that a patient taking diuretics should make some changes in his or her lifestyle, such as eating a low-sodium diet.
There are three main classes of diuretic medicines, each of which works a little differently.
- Thiazide diuretics moderately increase urine output and also act to widen blood vessels, helping to lower blood pressure in two ways. This is the most prescribed type of diuretic.
- Loop diuretics are stronger than thiazides. They produce more effective elimination of sodium and a greater increase in urine flow.
- Potassium-sparing diuretics are often prescribed in combination with thiazide and loop diuretics. As their name suggests, they help prevent the loss of too much potassium, which can be a problem with other types of diuretics.
Diuretic drugs sometimes become less effective over time, resulting in a condition called diuretic resistance. In some instances, diuretic resistance is treated with a non-drug therapy called ultrafiltration in which the excess fluid is filtered out of the blood.
Vasodilator drugs relax the smooth muscles that line blood vessel walls, causing the blood vessels to dilate and allow an increased amount of blood to flow through them. This has two beneficial effects -- it's easier for the heart to pump blood, and the blood pressure goes down. So, vasodilator drugs relieve symptoms associated with heart failure and treat high blood pressure. Uncontrolled high blood pressure puts a burden on the heart and the blood vessels that can lead to permanent damage over time, so controlling it is important.
There are two basic types of inotropic drugs: Positive inotropic drugs increase the force of the heart's muscular contractions, and negative inotropid drugs decrease it. By decreasing stress on the heart, negative inotropic drugs decrease blood pressure, the volume of blood that the heart pumps and electrical activity in the heart.
On the next page we'll learn about how and when doctors usually prescribe these drugs.