Pharmacology for Dentistry

Diuretics and Antidiuretics 209

i. It is widely used in the treatment of

hypertension and in the management

of refractory edema.

ii. Hypokalemia: Potassium sparing di-

uretics have been used in patients with

low serum K+ resulting from other di-

uretics, like thiazide and loop diuretics.

iii. Edema: It has been used in cirrhotic and

nephrotic edema.

OSMOTIC DIURETICS

Osmotic diuretics are non-electrolytes,
freely filterable at the glomerulus, undergo
limited reabsorption by the renal tubules.
The amount of diuresis produced is
proportional to the quantity of osmotic
diuretic, therefore for more diuresis, a large
quantity of osmotic diuretic should be given.
The primary effect of osmotic diuretics
involves an increased fluid loss caused by
osmotically active diuretic molecule. This
results in reduced reabsorption of sodium
and water in proximal tubule and since the
tubule is permeable to water, there is a
passive back diffusion of water, such a
process keeps the tubular fluid isotonic.

They also tend to increase glomerular
filtration rate.

MANNITOL

Mannitol is not absorbed from the GIT
and must be given IV and is osmotically
more active than urea.

Mannitol is useful in clinical conditions
which are characterized by hypotension and
decreased glomerular filtration. It is useful
in maintaining kidney function under these
conditions, even at low rates of filtration a
sufficient amount of mannitol may enter the

tubular fluid to exert an osmotic effect and

thus continue urine formation.

It is also used to reduce intraocular

pressure prior to eye surgery for glaucoma.

Mannitol has been used to reduce cerebral

edema.

The adverse reactions associated with

mannitol administration are nausea,

vomiting, headache and hypernatremia.

UREA

Urea is administered intravenously and

useful for reducing a raised cerebrospinal

fluid pressure during neurosurgery and

cerebral edema after head injury.

Urea is contraindicated in patients with

severe impairment of renal, hepatic or

cardiac function due to their potential effect

on expansion of the extracellular fluid

volume.

ISOSORBIDE

Isosorbide is an orally active diuretic,

most commonly used in the emergency

treatment of acute angle-closure glaucoma.

ORGANIC MERCURIALS

In earlier twenties, these agents were

diuretics of choice, but after the introduc-

tion of thiazides and loop diuretics, the

organomercurials have been almost re-

placed.

Mercurials depress the tubular

reabsorption of sodium at several sites

including loop of Henle and some portions

of proximal and distal tubules. They inhibit

the reabsorption of Cl– and Na+.