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Questions and Answers
What is the primary reason potassium-sparing diuretics are used in the management of congestive heart failure?
Which statement about loop diuretics is true?
What adverse effect is most commonly associated with the use of loop and thiazide diuretics?
Which factor does NOT determine the response to diuretic treatment in animals?
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What is the expected effect of administering a diuretic concurrently with an ACE inhibitor?
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Which class of diuretics is characterized by the ability to be administered in a dose-dependent manner to treat severe congestive heart failure?
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What common electrolyte disturbance is most closely associated with the use of loop and thiazide diuretics?
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How does the route of administration affect diuretic therapy effectiveness?
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What factor contributes most to the development of diuretic resistance during long-term treatment?
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Which of the following patient conditions increases the risk of digoxin toxicosis when treated with diuretics?
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Study Notes
Diuretics for Congestive Heart Failure
- Diuretics are a mainstay treatment option for congestive heart failure (CHF) in animals.
- Three primary classes of diuretics are used: loop diuretics, thiazide diuretics, and potassium-sparing diuretics.
- Loop diuretics are the most potent, acting in a dose-dependent manner to treat mild to severe CHF.
- Thiazide diuretics have moderate potency and are often used in conjunction with loop diuretics in severe cases.
- Potassium-sparing diuretics are typically used in cases of right heart failure, hypokalemia, or resistance to other agents, and also possess cardioprotective properties.
Furosemide: A Loop Diuretic
- Furosemide is the most commonly used diuretic for CHF in dogs, cats, cattle, and horses.
- It is available in oral and parenteral formulations.
- Furosemide inhibits sodium, potassium, and chloride reabsorption in the kidney, resulting in increased excretion of these electrolytes, along with water.
- This diuretic action leads to enhanced excretion of sodium, chloride, potassium, hydrogen, calcium, magnesium, and possibly phosphate.
- Furosemide also acts as a mild venodilator, reducing systemic venous pressure.
- The drug is highly protein-bound with rapid elimination, having a half-life of approximately 1 hour in dogs.
Adverse Effects of Diuretics
- All loop and thiazide diuretics can cause electrolyte and acid-base disturbances, dehydration, and kidney dysfunction.
- Common abnormalities include hypokalemia, hyponatremia, hypomagnesemia, and metabolic alkalosis.
- These effects are exacerbated by the use of multiple diuretics, concurrent anorexia, and higher doses.
- Cats are generally more susceptible to these adverse effects than dogs.
Diuretic Resistance
- Animals with CHF may become resistant to furosemide due to decreased drug delivery to the kidneys or hormonal factors promoting sodium and water retention.
- Strategies to increase renal blood flow or plasma concentration may mitigate resistance.
- Furosemide resistance should be considered if doses exceed 8-10 mg/kg for dogs and 6 mg/kg for cats.
Diuretics in CHF
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Diuretics are the primary treatment for CHF in animals, addressing issues like pulmonary edema, pleural effusion, and ascites.
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There are three main classes of diuretics used in veterinary medicine: Loop diuretics, Thiazide diuretics, and Potassium-sparing diuretics.
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Loop diuretics are the most potent. They are dosed in a way that scales with the severity of the CHF. They can be administered orally or intravenously.
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Thiazide diuretics are considered moderate in potency and are typically used alongside loop diuretics in cases of severe or resistant CHF.
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Potassium-sparing diuretics, like spironolactone, were historically reserved for animals with right heart failure or those experiencing hypokalemia from other diuretics. Now, they are used for their antifibrotic (cardioprotective) effects, blocking the effects of aldosterone on the heart.
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Adverse effects of loop and thiazide diuretics can include electrolyte and acid-base imbalances, dehydration, and kidney problems.
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The risk of kidney problems (azotemia) increases when diuretics are used alongside ACE inhibitors, NSAIDs, or other substances that can damage the kidneys.
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Diuretic resistance can develop with long-term use.
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Hypokalemia, hyponatremia, hypomagnesemia, and metabolic alkalosis are common electrolyte and acid-base problems linked to diuretics.
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The risk of these problems is higher in cats than dogs.
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Factors influencing diuretic response: potency, dosage, duration of action, route of administration, renal blood flow, glomerular filtration rate, and nephron function.
Furosemide
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Furosemide is the most common loop diuretic used in veterinary medicine for CHF. It's available in oral and injectable forms.
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Furosemide works by preventing reabsorption of sodium, potassium, and chloride in the ascending loop of Henle, ultimately reducing sodium and water absorption by the kidneys.
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Aside from its diuretic effect, furosemide also acts as a mild vasodilator, decreasing venous pressure before diuresis.
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The bioavailability of furosemide is influenced by the route of administration – intravenous administration yields higher plasma concentrations and a faster onset of action.
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Furosemide has a relatively short half-life of about 1 hour with peak effects occurring within 30 minutes of administration and a 2-3 hour duration of action.
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Furosemide resistance can occur in CHF due to decreased renal blood flow or hormonal changes promoting water retention.
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Increasing renal blood flow or the plasma concentration of furosemide may help overcome resistance.
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In dogs, furosemide resistance should be suspected if doses exceed 8-10 mg/kg daily. In cats, the threshold is about 6 mg/kg daily.
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Furosemide is significantly bound to proteins in the blood, and a small amount is metabolized in dogs, mainly to a glucuronide derivative.
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The drug is eliminated primarily through bile and urine in dogs, with approximately half cleared within the first 30 minutes of administration.
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Description
This quiz covers the role of diuretics in treating congestive heart failure (CHF) in animals. Learn about the different classes of diuretics, their mechanisms, and specific examples like furosemide. Assess your understanding of these essential pharmacological agents.
