Loop diuretic

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Diuretic loop is a diuretic that acts at the bottom of the loop of Henle in the kidneys. They are primarily used in medicine to treat hypertension and frequent edema due to congestive heart failure or renal insufficiency. While thiazide diuretics are more effective in patients with normal renal function, loop diuretics are more effective in patients with impaired renal function.

Video Loop diuretic

Action mechanism

The 90% diuretic loop is attached to the protein and is secreted into the convoluted proximal tubule through an organic anion transporter 1 (OAT-1), OAT-2, and ABCC4. Loop diuretics work on Na -K -2Cl ^- sympathizer (NKCC2) on thick ascending boughs of Henle arch to inhibit sodium, chloride and potassium reabsorption. This is achieved by competing for the Cl ^- binding site. Loop diuretics also inhibit NKCC2 in the macula densa, reducing sodium transported to macular densa cells. This stimulates the release of renin, which, through the renin-angiotensin system, increases fluid retention in the body, improves glomerular perfusion, thus increasing glomerular filtration rate (GFR). At the same time, the diuretic loop inhibits the tubuloglomerular feedback mechanism so that increased salt in the lumen near the macula densa does not trigger a response that reduces GFR.

Loop diuretics also inhibit magnesium and calcium reabsorption in upward thick boughs. The absorption of magnesium and calcium depends on the positive voltage on the luminal side and the less positive voltage on the interstitial side with a 10 mV transepithelial voltage gradient. This causes magnesium and calcium ions to be rejected from the luminal to the interstitial side, encouraging their absorption. The difference in voltage on both sides is regulated by recycled potassium through the medial outer potassium channel of the kidney. By inhibiting potassium recycling, the voltage gradient is removed and magnesium and calcium reabsorption are inhibited. By disrupting the reabsorption of these ions, loop diuretics prevent the formation of a hypertonic renal medulla. Without such a concentrated medulla, water has less osmotic drive force to leave the collecting duct system, which ultimately results in increased urine production. Loop diuretics lead to decreased renal blood flow by this mechanism. This diuresis leaves little water to be absorbed back into the blood, resulting in a decrease in blood volume.

The secondary effect of loop diuretics is to increase the production of prostaglandins, which produce vasodilation and increase blood supply to the kidneys.

The collective effect of decreased blood volume and vasodilation lowers blood pressure and improves edema.

Maps Loop diuretic

Pharmacokinetics

Loop diuretics are highly bonded with proteins and therefore have low distribution volumes. The nature of the protein bonds of the loop diuretic molecule causes it to be secreted through several transporter molecules along the proximal tubular luminal wall in order to exert its function. The availability of furosemide is a high variable from 10% to 90%. The biological half-life of furosemide is limited by the absorption of the digestive tract into the bloodstream. The apparent half-life of excretion is higher than the apparent absorption half-life of the oral route. Therefore, the intravenous furosemide dose is twice as strong as the oral route.

However, for torsemide and bumetanide, their oral bioavailability is consistently higher than 90%. Torsemide has a longer half-life in patients with heart failure (6 hours) when compared with furosemide (2.7 hours). Loop diuretics usually have a "ceiling" effect in which there is a maximum level of dosage where further dose increases will not increase the clinical effect of the drug. The dose of 40 mg of furosemide is equivalent to 20 mg of torsemide and 1 mg of bumetamide.

src: heartfailure.onlinejacc.org

Clinical use

Loop diuretics are mainly used in the following indications:

• Heart failure - Giving 2.5 times the previous oral twice daily dose to those with acute decompensated heart failure is a sensible strategy. However, a daily assessment of clinical response is needed to adjust the next dose.
• Edema is associated with liver cirrhosis, and nephrotic syndrome
• Cerebral edema - intravenous furosemide may be combined with mannitol to initiate rapid diuresis. However, the optimal duration of the treatment is still unknown. Frequent monitoring of fluid status is necessary to prevent intravascular volume depletion leading to decreased cerebral perfusion. An intravenous bolus dose of 10 or 20 mg of furosemide may be given and then followed by an intravenous bolus of 2 or 3% hypertonic saline to increase serum sodium levels.
• Lung edema - Intravenous dose bolus of 40 to 80 mg of furosemide at 4 mg per minute is indicated for patients with excess fluid and pulmonary odema. Such doses can be repeated after 20 minutes. After bolus, continuous intravenous infusion may be administered at 5 to 10 mg per hour. For those with underlying renal impairment or severe heart failure, up to 160-200 mg of bolus may be given.
• Hypertension - A systematic review by the Cochrane Hypertension group assessing the anti-hypertensive effect of loop diuretics found only a slight drop in blood pressure when compared with placebo. According to the Joint National Committee (JNC-8) guidelines, first-line treatment of hypertension is a thiazide diuretic. The use of loop diuretics is not mentioned in this guide. Meanwhile, according to the 2013 European Society of Cardiology (ESC) guidelines, loop diuretics can only replace thiazide-type diuretics if there is kidney damage (Creatinine is more than 1.5 mg/dL or the estimated glomerular filtration rate (eGFR) is less than 30 ml/min/1.73 m ² due to the lack of long-term cardiovascular outcome data and the appropriate dosing regimen of its use.

The 2012 KDIGO (Kidney Disease: Increase in Global Income) 2012 guideline states that diuretics should not be used to treat acute kidney injury, except for excessive volume management. Diuretics have not shown the benefit of preventing or treating acute kidney injury.

Sometimes it is also used in the management of severe hypercalcemia in combination with adequate rehydration.

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Resistance

Diuretic resistance is defined as a diuretic failure to reduce fluid retention (measurable with low urine sodium) despite the maximum drug dose. There are various causes of resistance to loop diuretics. After the initial period of diuresis, there will be a period of "post-diuretic sodium retention" in which the rate of sodium excretion does not reach as much as the initial diuresis period. Increasing sodium intake during this period will offset the amount of excreted sodium, and thus cause diuretic resistance. The use of loop diuretics too long will also contribute to the resistance through "braking phenomenon". It is the body's physiological response to reduce the volume of extracellular fluid, in which the renin-angiotensin-aldosterone system is activated which results in remodeling of the nephron. Nephrone renovation increases the number of distal twisted cells, principal cells, and intercalation cells. These cells have sympathizers of sodium chloride in intricate distal tubules, epithelial sodium channels, and chloride-bicarbonate exchanger pendrin. This will increase the reabsorption of sodium and fluid retention, causing diuretic resistance. Other factors include intestinal edema that slows the absorption of oral loop diuretics. Chronic kidney disease (CKD) reduces renal flow rate, reduces delivery of diuretic molecules to the nephrons, limits sodium excretion and increases sodium retention, causing diuretic resistance. Non-steroidal anti-inflammatory drugs (NSAIDs) can compete with loop diuretics for organic ion transporters, preventing diuretic molecules secreted into convoluted proximal tubules.

Those with diuretic resistance, cardiorenal syndrome, and severe right ventricular dysfunction may have a better response to a continuous diuretic infusion. The diuretic dose is adjusted to produce 3 to 5 liters of urine per day. Thiazide (blockade of the sodium-chloride symporter), amiloride (epithelial sodium channel blocker) and carbonic anhydrase inhibitor (chloride-bicarbonate pendrin blockade) have been suggested to complement the loop diuretic action in the case of resistance but limited evidence is available to support its use.

src: howmed.net

Adverse effects

The most common adverse drug reactions (ADRs) are dose related and arise from the diuretic loop effect on diuresis and electrolyte balance.

Common ADR includes: hyponatremia, hypokalemia, hypomagnesemia, dehydration, hyperuricemia, gout, dizziness, postural hypotension, syncope. The loss of magnesium as a result of loop diuretics has also been suggested as a possible cause of pseudogout (chondrocalcinosis)

Rarely ADRs include: dyslipidemia, elevated serum creatinine concentration, hypocalcemia, rash. Metabolic alkalosis can also be seen with the use of loop diuretics.

Ototoxicity (damage to the inner ear) is a serious, but rarely ADR associated with the use of loop diuretics. It may be confined to tinnitus and vertigo, but may cause deafness in serious cases.

Loop diuretics can also trigger kidney failure in patients who simultaneously take NSAIDs and ACE inhibitors - so-called "triple whammy" effects.

Because furosemide, torsemide and bumetanide are technically sulfa drugs, there is a theoretical risk that sulphonamide-sensitive patients may be sensitive to these loop diuretics. This risk is expressed on the drug packaging inserts. However, the true risk of crossreactivity is largely unknown and there are several sources that deny the existence of such cross reactivity. In one study it was found that only 10% of patients with allergies to sulfonamide antibiotics are also allergic to sulphonamides diuretics, but it is unclear whether this is a true cross reactivity or susceptibility to allergies.

Ethacrynic acid is the only drug of this class that is not sulfonamide. It has different complications associated with gastrointestinal toxicity.

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Diuretic loop example

• Furosemide
• Bumetanide
• Ethacrynic acid
• Torsemide

src: circheartfailure.ahajournals.org

References

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External links

• Diuretic Loop, from Family Practice Book
• Diuretic Loop at US National Library of Medicine's Medical Subject Headings (MeSH)

Source of the article : Wikipedia