Most sodium and water reabsorption occurs throughout the renal tubular seg-
ments. Diuretics affect one or more of these segments. Every one and one-half
hours the kidneys (glomeruli) clean the body’s extracellular fluid (ECF).
Small particles—such as electrolytes, drugs, glucose, and waste products
from protein metabolism—are filtered in the glomeruli during this process.
Sodium and water are the largest filtrate substances. Larger products—such as
protein and blood—are not filtered with normal renal function. Instead, they
remain in the circulation.
Nearly all filtered sodium is reabsorbed. Half occurs in the proximal tubules,
approximately 40% in the loop of Henle, about 7% in the distal tubules, and the
remaining in the collecting tubules.
Diuretics, such as Mannitol, that act on the tubules closest to the glomeruli
have the greatest effect in causing sodium loss in the urine (natriuresis).
Diuretics have an antihypertensive effect by promoting sodium and water
loss. They block sodium and chloride reabsorption causing a decrease in fluid
volume, a lowering of blood pressure, and a decrease of edema. If sodium is
retained, water is also retained in the body and blood pressure increases.
Many diuretics cause loss of other electrolytes, including potassium, magne-
sium, chloride, and bicarbonate. The diuretics that promote potassium excretion
are classified as potassium-wasting diuretics. Potassium-sparing diuretics pro-
mote the reabsorption of potassium. Combination diuretics have been marketed
that have both actions.
There are five categories of duretics that remove water and sodium.Thiazide and thiazide-like diuretics
Thiazide diuretics include: chlorothiazide (Diuril), hydrochlorothiazide
(HydroDIURIL, HCTZ), bendroflumethiazide (Naturetin), benzthiazide Aquatag,
(Hydrex), hydroflumethiazide (Saluron, Diucardin); methychlothiazide
(Aquatensen, Enduron), Polythiazide (Renese-R), trichlormethiazide (Metahydrin,
Naqua); Thyzaide-like diuretics: chlorthalidone (Hygroton), indapamide (Lozol),
metolazone (Zaroxolyn), and quinethazone (Hydromox).Loop or high-ceiling diuretics
Loop or high-ceiling diuretics include bumetanide (Bumex), ethacrynic acid
(Edecrin), furosemide (Lasix), and toresemide (Demadox).Osmotic diuretics
Osmotic diuretics include Mannitol and urea (Ureaphil).(^360) CHAPTER 19 Cardiac Circulatory Medications