Hypokalaemia is the Recognized Side Effect of Furosemide in Congestive Heart Failure
The answer is A. Hypokalaemia. Furosemide, a loop diuretic commonly used in congestive heart failure, is well-established to cause hypokalaemia as a major side effect through increased urinary potassium losses.
Evidence from Guidelines and Drug Labels
Hypokalaemia is explicitly listed as a major side effect of furosemide across multiple authoritative sources:
- The European Heart Journal guidelines (2001) clearly identify hypokalaemia, hypomagnesaemia, and hyponatraemia as major side effects of loop diuretics including furosemide 1
- The 2016 ESC guidelines emphasize that combination diuretic therapy requires careful monitoring to avoid hypokalaemia, renal dysfunction, and hypovolaemia 1
- The FDA drug label for furosemide states that "hypokalemia may develop with Furosemide tablets, especially with brisk diuresis, inadequate oral electrolyte intake, when cirrhosis is present, or during concomitant use of corticosteroids" 2
- The 2013 ACCF/AHA guidelines note that diuretics can cause electrolyte disturbances and recommend monitoring 1
Clinical Significance and Management
Hypokalaemia occurs through predictable mechanisms:
- Loop diuretics like furosemide inhibit sodium and chloride reabsorption in the ascending limb of the loop of Henle, leading to increased distal tubular sodium delivery and subsequent potassium-sodium exchange 1
- The risk increases with higher doses, inadequate oral potassium intake, and concurrent use of other medications that promote potassium loss 2
Guidelines recommend specific monitoring and prevention strategies:
- Potassium-sparing diuretics (triamterene, amiloride, spironolactone) should be used if hypokalaemia persists after initiation of therapy with ACE inhibitors and diuretics 1
- Regular monitoring of serum electrolytes (particularly potassium) is essential, with checks recommended 1-2 weeks after each dose increment, at 3 months, and subsequently at 6-monthly intervals 1
- Potassium supplements and/or dietary measures may be needed to control or avoid hypokalaemia 2
Research Evidence Supporting Hypokalaemia Risk
Clinical studies confirm the frequency of this adverse effect:
- A large surveillance study of 2,367 hospitalized patients receiving furosemide found that hypokalemia occurred in 3.6% of recipients, making it the second most common adverse reaction after intravascular volume depletion 3
- Among furosemide recipients who also received potassium supplements or potassium-sparing diuretics, hypokalemia was less frequent, less severe, and of slower onset 3
- The overall frequency of adverse reactions increased progressively with higher daily doses of furosemide 3
Why the Other Options Are Incorrect
B. Bronchospasm is not a recognized side effect of furosemide. This would be more characteristic of beta-blockers, which can cause bronchospasm in susceptible patients.
C. Hypoglycaemia is incorrect. In fact, furosemide causes the opposite effect—hyperglycemia. The FDA label explicitly states that "increases in blood glucose and alterations in glucose tolerance tests have been observed, and rarely, precipitation of diabetes mellitus has been reported" 2. Patients with diabetes mellitus should be told that furosemide may increase blood glucose levels 2.
D. Haemolytic anaemia is listed as a possible hematologic reaction in the FDA label 2, but it is extremely rare compared to hypokalaemia. The most common adverse reactions are electrolyte disturbances (hypokalaemia being the most clinically significant), intravascular volume depletion, and other electrolyte abnormalities 3.
Critical Clinical Pitfall
Digitalis therapy may exaggerate metabolic effects of hypokalaemia, especially myocardial effects 2. This is particularly important in heart failure patients who may be receiving both furosemide and digoxin, as hypokalaemia increases the risk of digoxin toxicity and cardiac arrhythmias.