CARBONIC ANHYDRASE INHIBITORS
The carbonic anhydrase inhibitors block the action of the enzyme carbonic anhy-
drase which is needed to maintain the acid-base balance (hydrogen and bicarbon-
ate ion balance). Inhibition of this enzyme causes increased sodium, potassium,
and bicarbonate excretion. Prolonged use can result in metabolic acidosis.
Carbonic anhydrase inhibitors include acetazolamide dichlorphenamide
(Diamox), and methazolamide (Daranide).
Carbonic anhydrase inhibitors are used to decrease intraocular pressure in
patients with open-angle (chronic) glaucoma and are not used in narrow-angle
or acute glaucoma. Other uses include inducing diuresis, management of epilepsy,
and treatment of high-altitude or acute mountain sickness.
Carbonic anhydrase inhibitors can cause fluid and electrolyte imbalance,
metabolic acidosis, nausea, vomiting, anorexia, confusion, orthostatic hypoten-
sion, and crystalluria. Hemolytic anemia and renal calculi can also occur. Carbonic
anhydrase inhibitors are contraindicated in the first trimester of pregnancy.
A list of drugs for carbonic anhydrase inhibitors is provided in the Appendix.
Detailed tables show doses, recommendations, expectations, side effects, con-
traindications, and more; available on the book’s Web site (see URL in Appendix).
POTASSIUM-SPARING DIURETICS
Potassium-sparing diuretics act primarily in the collecting distal duct renal
tubules to promote sodium and water excretion and potassium retention. The
drugs interfere with the sodium-potassium pump that is controlled by mineralo-
corticoid hormone aldosterone (sodium retained and potassium excreted).
Potassium is reabsorbed and sodium is excreted.
Potassium-sparing diuretics are weaker than thiazides and loops and are used
as mild diuretics or in combination with antihypertensive drugs. Continuous
use of potassium-wasting diuretics requires a daily oral potassium supplement
because potassium, sodium, and body water are excreted through the kidneys.
However, potassium supplements are not used when the patient takes potassium-
sparing diuretics.
When potassium-sparing diuretics are used alone they are less effective in
reducing body fluid and sodium than when used in combination. They are usu-
ally combined with a potassium-wasting diuretic, such as a thiazide or loop. The
combination intensifies the diuretic effect and prevents potassium loss. The main
side effect of these drugs is hyperkalemia.
CHAPTER 19 Cardiac Circulatory Medications^363