8-4. TYPES OF DIURETICS
There are several types of diuretics. The categories are defined
based upon their mechanism of action.
a. Osmotic Diuretics. Osmostic diuretics produce a diuresis of water rather
than a diuresis of sodium. The body does not metabolize osmotic diuretics. Instead,
the drug molecules are not reabsorbed in the kidney tubules. This greatly affects the
tonicity of every part of the kidney tubules through which the glomerular filtrates pass.
By the process of osmosis, the drug molecules draw an increased amount of water from
the interstitial fluid compartment. The result is that a great volume of urine is produced
(water diuresis). It just so happens that sodium is contained in that urine and is
subsequently removed from the body. Thus, the osmotic diuretics indirectly produce a
removal of sodium from the body. Following is one example of an osmotic diuretic:
Mannitol. Mannitol is used to prevent acute renal (kidney) failure, evaluate
kidney functioning, treat glaucoma (by the reduction of intraocular pressure), promote
the urinary excretion of toxic substances (diuresis in certain drug intoxications) and
reduce intracranial pressure (pressure in the head). The usual dosage of mannitol is
from 50 to 200 grams in a 24-hour period by intravenous infusion. Side effects
associated with the use of mannitol include pulmonary congestion, fluid and electrolyte
imbalance, acidosis, electrolyte loss, and dryness of mouth and dehydration. Since
mannitol may crystallize on exposure to low temperatures, you should observe mannitol
vials and premixed bags for such crystals. When you observe these crystals, you
should warm the vials or bags in a 500 C water bath in order to dissolve the crystals.
The product should be cooled to body temperature before the mannitol solution is
administered. Mannitol is available in a 5, 10, 15, 20, and 25 percent injection.
b. Thiazide Diuretics. Thiazide diuretics work by the inhibition of sodium
reabsorption in the first portion of the distal tubule. The passive diffusion of the
accompanying water and chloride is correspondingly reduced. Thus, the result is an
increased excretion of sodium, water, and chloride from the body. When the thiazide
acts on the proximal tubule, the carbonic anhydrase activity in the distal tubule is also
decreased. This causes increased secretion of potassium. Consequently, the water
lost contains sodium, potassium, and chloride. This loss of potassium can present
problems to the patient.
(1) Hydrochlorothiazide (Hydrodiuril). Hydrochlorothiazide is used in the
treatment of essential hypertension and edema found in congestive heart failure. The
usual dose of this drug is from 12.5 to 100 milligrams per day. Side effects commonly
associated with hydrochlorothiazide include hypokalemia, hyperglycemia, and
hyperuricemia. This drug should be used in caution in patients suffering from diabetes
or gout and in patients who take digitalis.