Diuretics work by reducing the amount of water and salt in the body. Since blood pressure can be influenced by salt intake, diuretics are the first line drugs for treating high blood pressure.
There are three main types of diuretics: thiazides, loop, and potassium-sparing agents. All three types lower the amount of salt and water in the body, helping to lower blood pressure. They differ in the area of kidney where they work.
- Thiazides reduce sodium absorption from the distal tubule segment of the kidney. They can be taken alone to treat mild to moderate high blood pressure or taken in combination with other drugs. Some common thiazides and thiazide-containing drugs are: chlorothiazide (Diuril®), chlorthalidone (Hygroton®), indapamide (Lozol®), and hydrochlorothiazide (Esidrix®, HydroDiuril®).
- Loop diuretics also block sodium absorption from the kidney back into the blood, but they tend to work faster than thiazides and have a greater effect since they work in the Loop of Henle in the kidney. Loop diuretics need to be monitored and controlled in order to prevent dehydration and excessive loss of potassium. Some common loop diuretics include bumetanide (Bumex®), furosemide (Lasix®), and ethacrynic acid (Edecrin®).
- Potassium-sparing agents block the action of aldosterone in the collecting duct of the kidney, so that more potassium is left in the blood. Leaving more potassium in the blood causes more sodium and water to be excreted in the urine. Some examples of such medications include amiloride (Midamor®), spironolactone (Aldactone®), and triamterene (Dyrenium®).
Common Side Effects
As with most other medications, there are some problems associated with diuretics. Electrolytes such as potassium and sodium are important to the body. Loop and thiazide diuretics can deplete the body’s supply of potassium, which if untreated, could ultimately cause irregular heartbeats (cardiac arrythmias). In rare instances, such heart rhythm disturbances can lead to cardiac arrest. Potassium-sparing drugs, on the contrary possess the risk of raising potassium levels to dangerously high levels. Other common side effects include:
- Muscle cramps, fatigue, weakness due to low potassium levels
- Increased sensitivity to sunlight
- Dizziness/light-headedness
- Heart palpitations/arrythmias
- Urinary frequency
- Allergic reactions in patients with sulfa allergies
- Loop and thiazide diuretics may raise cholesterol or blood sugar levels.
- Potassium-sparing diuretics can contribute to decreased sexual drive; increased hair growth, menstrual changes, breast tenderness, and breast swelling in men.
Drug Interactions
- Digoxin: Enhanced digoxin-toxicity when potassium blood concentrations are reduced with a diuretic
- Drugs used to treat diabetes: Decreased effectiveness due to diuretics causing an increase in blood glucose
- Drugs used to treat high blood pressure: Other high blood pressure medications may be additive in reducing blood pressure further
- Drugs used to treat high cholesterol: Decreased effectiveness due to diuretics causing an increase in cholesterol
- Nonsteroidal anti-inflammatory drugs (NSAIDS) – Decreased effectiveness of diuretics since NSAIDS can increase sodium retention.
Patient Instructions
- May be taken with food or milk
- Rise slowly from a lying or seated position to reduce the risk of dizziness or light-headedness
- Take evening dose early in evening to avoid awakenings due to increased urinary frequency.
- Consult your physician about the need to withhold doses in the event of diarrhea or vomiting in order to prevent dehydration.
