Pharmacology-Diuretics and Drugs for Electrolyte and Acid-Base Disorders

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Pharmacologic class: Thiazide Diuretic
Therapeutic class: anithypertensice, agent for reducing edema

Chlorothiazide (Diuril)

Pharmacologic class: K+-sparing Diuretic
Therapeutic class: Antihypertensive, drug for reducing edema

Spironolactone (Aldactone)

Pharmacologic class: Alkaline Agent/Electrolyte
Therapeutic class: agent to treat acidosis or bicarbinate deficiency

Sodium Bicarbonate

Pharmacologic class: Electrolyte
Therapeutic class: Potassium supplement

Potassium Chloride

The kidneys regulate fluid volume, electrolytes, acids, and bases

Kidneys are essential to overall health

Primary organs for controlling fluid volume, electrolyte composition, and acid-base balance

Functional unit of the kidney is the NEPHRON¹

The kidneys regulate fluid volume, electrolytes, acids, and bases

Additional kidney functions

Secrete renin - regulate blood pressure

Secrete erythropoietin - stimulates red blood cell production

Produce calcitrol (active form of vitamin D) - help maintain bone homeostasis

The kidneys regulate fluid volume, electrolytes, acids, and bases

Structures of the urinary system
Two kidneys
Two ureters
One urinary bladder
One urethra

The kidneys regulate fluid volume, electrolytes, acids, and bases

Blood enters a nephron at Bowman's capsule
Fluid is called filtrate
Water and small molecules pass into the proximal tubule
Filtrate passes through loop of Henle, then the distal tubule
Nephrons empty filtrate into collecting ducts
The fluid in collecting ducts is called urine

The composition of filtrate changes dramatically as a result of the processes of reabsorption and secretion

Filtrate passing through Bowman's capsule has the same composition as plasma minus large proteins
Reabsorption - some substances in the filtrate cross the walls of the nephron and reenter the blood
Water is the most important molecule reabsorbed in the tubule
Glucose, amino acids, sodium, chloride, calcium, and bicarbonate are also reabsorbed
Some ions and molecules are too large to pass through Bowman's capsule, but enter the filtrate through ...
Secretion - some substances pass from the blood through the walls of the nephron and become part of the filtrate
Potassium, phosphate, hydrogen, ammonium ion, and many organic acids are secreted into the filtrate

Renal failure significantly impacts pharmacotherapy

Kidneys excrete most drugs

Patients with moderate to severe renal failure require a smaller dose of a large # of drugs

Pharmacotherapy of renal failure attempts to CURE the cause of the dysfunction

Renal failure significantly impacts pharmacotherapy

iuretics - used to maintain urine output

Epoetin alfa (form of erythropoietin) is used to treat anemia (deficiency in red blood cell production)

Renal failure

Acute
Requires immediate treatment
Accumulation of waste products can be fatal
Cause of acute renal failure is insufficient blood flow
Cause must be rapidly identified and corrected
Heart failure
Dysrhythmias
Hemorrhage
Dehydration
Chronic
Occurs over months or years
Many cases occur in patients with a history of hypertension or diabetes mellitus
May be undiagnosed for a long time

Diuretics are used to treat HTN, HF, and fluid retention disorders - Most diuretics act by blocking sodium reabsorption in the nephron

Diuretics = ↑ urine output
By blocking Na+ reabsorption
Blocking reabsorption of Na+ keeps more water in the filtrate
The more water in the filtrate, the greater the volume of urine
Different diuretics act at different sites along the nephron

Most effective diuretics are those that affect the loop of Henl

Loop diuretics (furosemide) act by blocking Na+ reabsorption in the loop of Henle
The most effective diuretics, BUT are more likely to cause dehydration and electrolyte loss (rapid excretion of large amounts of water)
Used to reduce edema associated with:
Heart failure
Hepatic cirrhosis
Chronic renal failure
Loop diuretics reserved for clients with moderate to severe fluid retention

The thiazides are the most widely prescribed class of diuretics

Thiazide diuretics block Na+ reabsorption in the distal tubule

Less effective than LOOP diuretics

More frequently prescribed; however, d/t their lower incidence of serious side effects

Used to treat mild to moderate hypertension

Not effective in clients with severe renal disease

Although less effective than loop diuretics, potassium -sparing diuretics may help prevent hypokalemia

K+ -sparing diuretics act on the distal tubule
Less effective than loop diuretics
Produce a mild diuresis without affecting blood potassium levels
Block the exchange between sodium and potassium in the tubule
Causes sodium to stay in the tubule and leave through the urine
More potassium is retained by the body

Several less commonly prescribed diuretics have specific indications

Carbonic anhydrase inhibitors
Prevent formation of carbonic acid water and carbon dioxide
Example - acetazolamide (Diamox)
Decreases intraocular fluid pressure in patients with glaucoma
Osmotic diuretics
Maintain urine flow in clients with acute renal failure or during prolonged surgery
Example - mannitol
Very potent diuretic; only given IV

Electrolytes are charged substances that play important roles in body chemistry

Electrolyte imbalances can cause serious problems
Small, inorganic molecules possessing a positive or negative charge
Essential for body functions
Nerve conduction
Muscle contraction
Bone growth and remodeling
Kidney and GI tract are the primary regulators
Balance of sodium, potassium, and calcium is of greatest importance

Electrolytes are charged substances that play important roles in body chemistry

SODIUM:
Hypernatremia
Most commonly caused by kidney disease
Accumulates due to decreased excretion
Minor hypernatremia - low salt diet
Acute hypernatremia - IV fluids and diuretics

Hyponatremia
Caused by disorders that cause sodium to be lost
Disorders of the skin, GI tract, or kidneys
Excessive sweating
Prolonged fever
Increased risk when patients are taking potassium-sparing diuretics
Treat with IV solutions of sodium chloride

Electrolytes are charged substances that play important roles in body chemistry

POTASSIUM
Hypokalemia
Caused by:
High doses of loop diuretics
Strenuous muscle activity
Severe vomiting or diarrhea
Mild - increase dietary intake of potassium
More severe - oral or parenteral potassium supplements

Acidic and basic drugs can be administered to maintain normal body pH

pH measures the degree of acidity or alkalinity of a solution
A pH of 7.0 is neutral
A pH above 7.0 is basic or alkaline
A pH below 7.0 is acidic
pH of plasma and most body fluids is between 7.35 and 7.45

Acidic and basic drugs can be administered to maintain normal body pH

Alkalosis
Develops at pH values above 7.45
Symptoms of CNS stimulation - nervousness and convulsions
May be fatal if large change in pH not corrected immediately
Common causes - see Table 27.5
Ammonium chloride = quickly reverse alkalosis
Sodium chloride w/ potassium chloride can reverse alkalosis indirectly

Acidic and basic drugs can be administered to maintain normal body pH

Acidosis
Develops at pH values below 7.35
Symptoms of CNS depression - coma
May be fatal if large change in pH not corrected immediately
Common causes - see Table 27.5
More common than alkalosis
Sodium bicarbonate drug of choice

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