Loop diuretics

Question 1

Example of a Loop diuretic

Answer 1

Furosemide

Question 2

How does Furosemide work?

Answer 2

Loop diuretics act on the ascending limb of the loop of Henle, where they inhibit the Na+/K+/2Cl−co-transporter. This protein is responsible for transporting sodium, potassium and chloride ions from the tubular lumen into the epithelial cell. Water then follows by osmosis. Inhibiting this process has a potent diuretic effect.

Loop diuretics have a direct effect on blood vessels, causing dilatation of capacitance veins. In acute heart failure, this reduces preload and improves contractile function of the ‘overstretched’ heart muscle.

Question 3

Indications of furosemide

Answer 3

Acute pulmonary oedema: relief of breathlessness in conjunction with oxygen and nitrates.

Chronic heart failure. symptomatic treatment of fluid overload

Other oedematous states, e.g. due to renal disease or liver failure

Question 4

Contraindications of furosemide

Answer 4

Patients with severe hypovolemia or dehydration.

Used with caution in patients at risk of hepatic encephalopathy (where hypokalaemia can cause/ worsen coma) and those with severe hypokalaemia and/or hyponatraemia.

Taken chronically, loop diuretics inhibit uric acid excretion and this can worsen gout.

Question 5

Side effects of furosemide

Answer 5

C lead to dehydration and hypotension.

Inhibiting the Na+/K+/2Cl− co-transporter increases urinary losses of sodium, potassium and chloride ions. Indirectly, this also increases excretion of magnesium, calcium and hydrogen ions. You can therefore associate loop diuretics with almost any low electrolyte state (i.e. hyponatraemia, hypokalaemia, hypochloraemia, hypocalcaemia, hypomagnesaemia and metabolic alkalosis).

A similar Na+/K+/2Cl− co-transporter is responsible for regulating endolymph composition in the inner ear. At high doses, loop diuretics can affect this, leading to hearing loss and tinnitus.i

Question 6

Possible interactions of furosemide

Answer 6

Have potential to affect drugs that are excreted by the kidneys. For example, lithium levels are increased due to reduced excretion. The risk of digoxin toxicity may also be increased, due to the effects of diuretic-associated hypokalaemia.

Loop diuretics can increase the ototoxicity and nephrotoxicity of aminoglycosides.

Question 7

Elimination of furosemide

Answer 7

Renal

Question 8

Patient information

Answer 8

Furosemide 40 mg IV (oral also available)

Explain to your patient that their body is overloaded with water. You are therefore offering a treatment to increase urine flow, which will hopefully improve this. The medicine will inevitably cause them to need to pass water more often. Provided they do not take doses late in the day it should not affect them at night.