In addition to prescription diuretics, there are
several types of diuretics available in over-the-counter
formulations or commonplace beverages.
Loop diuretics are the strongest
of the prescription diuretics. They take their name from
the fact that they work in the ascending limb of the loop
of Henle, a structure in the kidney in which magnesium
and calcium are ordinarily reabsorbed. By disrupting
the reabsorption of these two ions, loop diuretics bring
about increased urine production, which in turn lowers
blood volume, leading to lowered blood pressure. Loop
diuretics also cause the veins to dilate, which lowers
blood pressure mechanically. This vasodilation is independent
of the drug’s diuretic effect.
Loop diuretics are usually given to treat edema
(accumulation of fluid in body tissues) associated with
heart failure; cirrhosis of the liver; impaired kidney
function or nephrotic syndrome (a condition in which
the kidneys leak protein from blood into the urine);
hypertension; or severe hypercalcemia (abnormally high levels of calcium in the blood). They are also
given together with other drugs to treat edema of the
brain or lungs, conditions that require rapid diuresis.
Drugs classified as loop diuretics include furosemide
(Lasix), bumetanide (Bumex), ethacrynic acid (Edecrin),
and torsemide (Demadex).
Thiazide diuretics are derived
froma chemical called benzothiadi(A)zene. Unlike the
loop diuretics, which work in the loop of Henle, thiazide
diuretics work in a different structure called the
distal convoluted tubule, although they function in a
similar way to increase urine production by decreasing
the kidney’s reabsorption of sodium and calcium.
They are not as strong as loop diuretics and have
fewer adverse effects.
Thiazide diuretics are commonly prescribed to
manage high blood pressure because they help to
dilate blood vessels as well as lower blood volume by
increasing urine output. They are also sometimes
given to patients with high levels of calcium in the
urine to prevent the formation of kidney stones and
lower the risk of osteoporosis. They include such
drugs as hydrochlorothiazide (HydroDiuril, Esidrix),
chlorothiazide (Diachlor, Diuril), and chlorthalidone
(Hygroton, Hylidone).
Potassium-sparing
diuretics include such drugs as amiloride (Midamor)
and triamterene (Dyrenium). They are usually given
together with loop diuretics in treating CHF or high
blood pressure to prevent the patient’s potassium level
from falling too low. They work by decreasing sodium
reabsorption in the collecting tubules of the kidneys.
There are two formulations that combine the
potassium-sparing diuretic triamterene with the thiazide
diuretic hydrochlorothiazide in one pill—Maxzide
and Dyazide—thus simplifying the patient’s dosage
schedule.
Osmotic diuretics are substances
that cannot be reabsorbed in the kidney and
so increase urine volume by osmosis. The most commonly
used osmotic diuretic is mannitol, a sugar alcohol
or polyol that is also added to sugar-free candies,
mouthwashes, and similar products as an artificial
sweetener. Mannitol (Osmitrol) is given intravenously
to patients with glaucoma to lower fluid pressure
inside they eyeball, and to patients with acute kidney
failure following cardiovascular surgery.
Until early 2007, high-dose mannitol was recommended
as treatment to reduce fluid accumulation
inside the skull in cases of head trauma, on the basis
of randomized trials conducted by a neurosurgeon in
Brazil who committed suicide in 2005. His papers on
the use of mannitol in head surgery were called into
question in late 2006; neither his former coauthors nor
the journal editors who published his studies have
been able to verify his data; and the university he
claimed as his affiliation has never employed him.
Carbonic anhydrase
inhibitors are a class of diuretics that increase
water loss through the kidneys by changing the acidity
of urine. Their most common use, however, is to treat
glaucoma by lowering the fluid pressure inside the
eyeball. The most common diuretic in this group,
acetazolamide (Diamox), is also used as an anticonvulsant
(drug given to prevent seizures). Other carbonic
anhydrase inhibitors include dichlorphenamide
(Daranide) and methazolamide (Neptazane).
Prescription diuretics should be used only under a
doctor’s supervision and monitored in long-term
users, as dosage requirements may change or the doctor
may recommend dietary supplements to compensate
for electrolytes and nutrients lost through the use
of some diuretics. In addition, patients should not stop
taking prescription diuretics or change the dosage
without consulting their doctor.
