Furosemide

Question 1

What class of drug does it belong to?

Answer 1

Loop Diuretic

Question 2

How does it work?

Answer 2

Have at thiazide-like action on early distal tubule (inhibit NaCl reabsorption), but much more importantly, they inhibit NaCl reabsorption in the thick ascending loop of Henle. This segment has a high capacity for absorbing NaCl and so drugs which act on this site produce a diuresis much greater than other diuretics.
Act within 1 hour and diuresis complete with 6 hours.

Question 3

Indications?

Answer 3

• Pulmonary odema due to left hear failure.
• Chronic heart failre.
• Can be added to antihypertensive treatment to achieve better control.

Question 4

Contra-indications?

Answer 4

Should be avoided in severe hypokalaemia, severe hyponatraemia, anuria, comatose and precomatose states associated with liver cirrhosis, and in renal failure due to nephrotoxic or hepatotoxic drugs.

Question 5

Side-effects?

Answer 5

1. Hypokalaemia – increased Na+ load stimulates Na+ exchange with K+ and H+, increasing their excretion.
2. Hyperuricaemia – Uric acid levels in blood often increased because thiazides/loop diuretics are secreted by the organic acid secretory system in the tubules and compete for uric acid secretion. May precipitate gout.
3. Hyperglycaemia – Glucose tolerance may be impaired and thiazides are contraindicated in people with type II diabetes.
4. Overenthusiastic use of loop diuretics can cause deafness, which may not be reversible.

Question 6

Possible interactions?

Answer 6

Antihypertensives – enhanced hypotensive effect possible with all types. Concurrent use with ACE inhibitors or Angiotensin II receptor antagonists can result in marked falls in blood pressure, furosemide should be stopped or the dose reduced before starting an ACE-inhibitor or Angiotensin II receptor antagonists.

Antipsychotics – furosemide-induced hypokalaemia increases the risk of cardiac toxicity. Avoid concurrent use with pimozide. Increased risk of ventricular arrhythmias with pimozide (avoid concurrent use), amisulpride or sertindole. Enhanced hypotensive effect with phenothiazines.

Anti-arrhythmics (including amiodarone, disopyramide, flecainide and sotalol) - risk of cardiac toxicity (because of furosemide-induced hypokalaemia). The effects of lidocaine, tocainide or mexiletine may be antagonised by furosemide.

Cardiac glycosides – hypokalaemia and electrolyte disturbances (including hypomagnesemia) increase the risk of cardiac toxicity.

Question 7

Elimination?

Answer 7

In about 6-8 hours.