Pharmacology and Nutrition

LEARNING OUTCOMES

After studying this chapter, the student will be able to:

1. List the major health problems for which treatment with diuretic drugs is used

2. List the major classes of diuretics, their mechanism of action and their side effects

 

DIURETICS

Drugs used to remove sodium and water from the body. They are clinically employed in clients with edema or ascites, both of which are pathological increases in extracellular fluid volume. Diuretics are also used in the treatment of hypertension, as they can promote blood pressure reduction while reducing the adverse effects of other antihypertensive drugs.

DIURETICS AND ANTIHYPERTENSIVES

on the concentration of the hormone, aldosterone. The regulation of sodium balance by the kidney is therefore determined by: glomerular filtration rate (i.e., the rate at which fluid is filtered by the kidney glomeruli) concentration of aldosterone, a hormone secreted by the adrenal cortex baroreceptors of the body In certain illnesses the excretion of sodium may be impaired, thus leading to the accumulation of fluid and sodium within the body. Diuretics are designed to correct this situation by promoting the excretion of sodium by inhibiting its reabsorption.

Thiazide Diuretics

The thiazide diuretics were developed in the 1950s and have evolved to be the safest diuretic agents in current use. They appear to act by inhibiting sodium and chloride reabsorption in the early portion of the distal tubule, although they may also block chloride reabsorption in the ascending hoop of Henle. As the concentration of sodium reaching the distal tubule is higher in clients using thiazide diuretics, a greater than normal sodium-potassium exchange takes place, thereby possibly leading to potassium depletion and hypokalemia. Because of the neurotransmission importance of potassium, its depletion can have serious, even life-threatening, consequences. Neurotransmitters conduct impulses to muscles of the body including and most particularly the heart. Thus, with insufficient potassium, clients may experience cardiac arrhythmias, as well as muscle weakness in skeletal and smooth muscles of the body. In addition, an excessive amount of chloride is also sometimes excreted by such clients, thereby leading to chloride depletion and metabolic alkalosis.

Note:

These drugs may cause hyperuricemia and hyperglycemia.

Carefully monitor clients with gout or diabetes mellitus.

Monitor potassium level and assess client for hypokalemia, including symptoms of muscle cramps and weakness.

Encourage intake of potassium-rich foods, including citrus fruits, bananas, and apricots.

Give drug early in the day to prevent nocturia.

Record intake and output on hospitalized clients.

Monitor blood pressure and weight.

Observe clients taking thiazide diuretics with cardiac glycosides for the development of cardiac glycoside toxicity (visual disorders, bradycardia, bigeminy, nausea, vomiting, and anorexia).

Use of alcohol, barbiturates or narcotics may aggravate postural hypotension.

Discontinue drug use before parathyroid function tests are performed.

 

Loop Diuretics

Loop diuretics, furosemide (Lasix), ethacrynic acid (Edecrin), bumetanide (Bumex), and torsemide (Demadex) are widely used. These agents act by inhibiting the reabsorption of sodium and chloride in the ascending loop of Henle, thereby reducing the ability of the kidneys to concentrate urine. The loop diuretics are considerably more potent than the thiazides in promoting sodium and fluid excretion. Unlike the thiazides, they remain effective, even in clients with seriously impaired glomerular filtration rates. This has made them popular agents in treating elderly clients, who may not adequately respond to thiazides. Because of the relatively high concentration of sodium that enters the distal tubule, considerable sodium-potassium exchange occurs in clients using loop diuretics, thereby promoting the development of hypokalemia. The use of these agents has also been associated with hearing loss, particularly when administered parenterally in high doses.

Potassium-Sparing Diuretics

Several agents having diuretic activity, but different modes of action, exert their action in the distal tubule. Spironolactone (Aldactone) imparts its diuretic activity by inhibiting the action of the hormone aldosterone. Triamterene (Dyrenium) and amiloride HCl (Midamor) directly block sodium reabsorption in the distal tubule independently of aldosterone. None of these agents is a potent diuretic.

Osmotic Diuretics

Osmotic diuretics are agents capable of being filtered by the glomerulus, but have a limited capability of being reabsorbed into the bloodstream. This results in a high concentration of osmotic agent in the kidney tubule, which leads to large amounts of fluid and produces a profound diuretic effect. Agents such as glycerin and isosorbide are used orally. Urea and mannitol are administered intravenously as osmotic diuretics. They are employed primarily in the treatment of increased intracranial pressure, but is also used to treat acute renal failure as well as in conditions where rapid reduction of the pressure and volume of intraocular and/or intraspinal fluid is required.

Carbonic Anhydrase Inhibitors

Carbonic anhydrase is an enzyme found in a number of organs of the body, including kidneys and eyes. In kidneys, the enzyme acts to promote the reabsorption of sodium and bicarbonate from the proximal tubule, thereby maintaining the alkalinity of the blood. The administration of drugs such as acetazolamide (Diamox), dichlorphenamide (Daranide), and methazolamide (Neptazane) that inhibit carbonic anhydrase activity, promotes the excretion of bicarbonate, sodium and water, and results in a mild diuretic effect.

The use of carbonic anhydrase inhibitors as diuretics has diminished greatly with the development of more effective diuretic drugs. These agents are used widely, however, for the reduction of intraocular pressure in glaucoma clients (review Chapter 26). This application is based upon the observation that inhibition of carbonic anhydrase activity reduces the rate of production of aqueous humor in the eye.

Non-thiazide Diuretics

Note:

Give early in the day to prevent nocturia.

Record intake and output in hospitalized clients.

Monitor fluid and electrolyte balance, especially potassium.

 Observe clients taking cardiac glycosides and diuretics, other than potassium-sparing diuretics, for the development of cardiac glycoside toxicity (visual disturbances, bradycardia, bigeminy, nausea, vomiting, and anorexia).

Monitor blood pressure and weight.

Diuretics

Oral diuretics have long been considered to be the cornerstone of antihypertensive drug therapy and are often used as the initial form of treatment. Most of these agents have been shown to be capable of lowering both systolic and diastolic blood pressure in virtually all clients treated for essential hypertension. They will also potentiate the action of most other oral, nondiuretic, antihypertensive agents.

 

Nondiuretic Antihypertensive Agents

Note:

Client education program should stress the importance of compliance.

Monitor blood pressure. If postural hypotension occurs, teach client to change position slowly, especially on first rising in the morning. Elastic stockings or ingesting a high-protein snack at bedtime may also be helpful.

Clients on sodium-restricted diets require special instruction and follow-up.

 

Assessment

1. In measuring blood pressure, use an appropriate size cuff.

2. If a reading of 140/90 or higher is obtained, check the blood pressure in the other arm, take a personal, family, and medication history and observe the client’s level of anxiety.

3. Refer clients to the physician if they have three elevated readings 1 week apart.

 4. Ongoing assessment includes blood pressure readings, weight, inquiries about diet, alcohol intake, exercise, smoking, and problems related to medication

Sodium and Potassium Needs

1. Some clients with hypertension benefit from a sodium restricted diet, either mild (1,500–2,000 mg), moderate (1,000 mg) or severe (500 mg).

2. Clients on sodium-restricted diets may experience sodium deficit, particularly during hot weather. A temporary increase in sodium is recommended.

3. Muscle cramps, muscle weakness, and change in the pulse may indicate potassium deficit. Potassium is replaced by intake of foods such as fruits and fruit juices.

 4. Clients on sodium-restricted diets must be taught to read the labels on foods and medications to identify sources of sodium.

5. Clients taking potassium-sparing diuretics are instructed to avoid salt substitutes containing potassium.

Limiting Adverse Effects

1. Cooperation may be enhanced when the unpleasant side effects of therapy are controlled.

2. Assess blood pressure, weight, tissue turgor, and indications of low serum potassium such as muscle weakness, leg cramps and pulse irregularities.

 3. Maintain intake and output records for all hospitalized clients taking diuretics.

4. Use of thiazide diuretics may result in hyperglycemia, with both thiazides and ethacrynic acid possibly increasing serum uric acid levels. Diabetics and those with gout must be monitored carefully.

5. Rauwolfia derivatives may produce nasal stuffiness and mental depression. Clients are advised to avoid the use of over-the counter decongestants containing pressor agents. Therapy may be discontinued if the client becomes depressed.

6. Postural hypotension is alleviated by changing positions slowly, eating a high protein snack at night, flexing the calf muscles to increase blood return to the heart and wearing elastic stockings or a counter-pressure garment. Clients are cautioned to avoid alcohol and straining at stool and to hold onto a stationary object when rising.

7. Observe clients taking beta-adrenergic blocking agents for respiratory difficulties and bradycardia. Diabetics are monitored for hypoglycemia. All clients are instructed to protect the extremities from cold.

8. Clients taking antihypertensives should tell other health care personnel that they are taking these drugs.

9. Observe the elderly for orthostatic hypotension and protect them from falls.

 

Long-Term Client Management

1. Clients are advised to avoid heavy meals and exercise after meals.

2. Straining at stool is contraindicated, and measures should be taken to prevent constipation.

 3. Weight loss is recommended, and clients who smoke should be encouraged to quit.

4. Aerobic exercise, avoidance of alcohol, and a diet rich in potassium and calcium may all be important in controlling blood pressure.

5. Clients should learn coping measures to deal with stress.

 6. Clients are instructed to read the labels of over-the-counter (OTC) drugs since many of them contain pressor substances contraindicated in hypertension

Hypertensive Emergencies

1. A hypertensive emergency exists when the diastolic blood pressure exceeds 120 mm Hg and there is evidence of end organ damage.

2. Medications, such as sodium nitroprusside or diazoxide, will be administered intravenously.

3. Monitor the vital and neurologic signs and report significant changes.