Loop diuretics

Question 1

MoA

Answer 1

Inhibits Na+/K+/Cl- co-transporter in the ascending limb of loop of Henle.

More detail:
- Responsible for transporting sodium, potassium and chloride ions from the lumen into cells.
- Water follows by osmosis.
- Inhibiting reabsorption = less water follows.

Question 2

Indications

Answer 2

• Relief of breathlessness in acute pulmonary oedema in combination with O2 + nitrates.
• Fluid overload in chronic HF
• Fluid overload in other oedematic states (e.g. renal disease/liver failure)

Question 3

How long do they take to work?

Answer 3

• 1 hour onset
• 6 hour duration

Question 4

Acute pulmonary oedema

Answer 4

IV furosemide (40 mg)
Then, oral maintenance doses.

Question 5

Side effects

Answer 5

• Dehydration
• Hypotension
• Low electrolyte state
• Ototoxicity (hearing loss/tinnitus)

Question 6

Low electrolyte state

Answer 6

• Increased urinary loss of sodium, potassium and chloride ions indirectly increases excretion of magnesium, calcium and hydrogen.
• Hyponatraemia
• Hypokalaemia
• Hypochloraemia
• Hypomagnesaemia
• Metabolic alkalosis (hypocalcaemia)

Question 7

Contraindications

Answer 7

Severe hypovolemia and dehydration

Question 8

Cautions

Answer 8

Hypokalaemia
Hyponatraemia
People at risk of hepatic encelopathy
Gout (chronic use = inhibits uric acid secretion)
Diabetes (can cause hyperglycaemia BUT less likely than thiazides)
BPH (can cause urinary retention)

Question 9

Interactions

Answer 9

Drugs that are renally excreted (e.g. lithium) - increases Cp levels of these drugs.

Digoxin - increased risk of toxicity due to diuretic-associated hypokalaemia

Aminoglycosides - increases risk of ototoxicity and nephrotoxicity

Question 10

Heart failure

Answer 10

Furosemide = 20-40 mg OM. Can be increased up to 120 mg.
Can be taken BD if necessary, last dose taken at 4pm

Question 11

Resistant hypertension

Answer 11

Bumetanide (most potent)
Torasemide (musculoskeletal pain)
Furosemide

Question 12

Monitoring

Answer 12

Electrolytes