EXAMPLES
Furosemide, bumetanide
MECHANISM OF ACTION
- Inhibits the reabsorption of Na+ and Cl in the ascending limb of the Loop of Henle by inhibiting the Na+/K+/2Cl co-transporter.
- This results in increased Naþ excretion and free water clearance, thereby reducing preload.
INDICATIONS
- Pulmonary oedema is secondary to LVF.
- Chronic heart failure
CAUTIONS AND CONTRA-INDICATIONS
- Severe hypokalaemia/hyponatraemia.
- Hypovolaemia.
- Renal failure due to nephrotoxic drugs.
- Comatose patients with liver cirrhosis.
- Anuria.
SIDE-EFFECTS
- Electrolyte disturbances (hypokalaemia, hyponatraemia, hypocalcaemia). Hypotension.
- Tinnitus and deafness (associated with large IV boluses).
- GI disturbance.
- Dyslipidaemia
METABOLISM AND HALF-LIFE
- t½ is variable (furosemide 90 min).
- The onset of action occurs within 1h and diuresis is complete within 6 h.
- Excreted largely unchanged in the urine.
MONITORING
- Check U&Es prior to initiating and during treatment.
DRUG INTERACTIONS
- Risk of cardiotoxicity when given with digoxin (secondary to hypokalaemia).
- Risk of ototoxicity when given with aminoglycosides or vancomycin.
- Enhanced hypotensive effect with other antihypertensives.
- Can reduce lithium excretion.
- NSAIDs can reduce the effectiveness of loop diuretics (due to reduced GFR)
IMPORTANT POINTS
- Patients with low GFR may require higher doses(diuretic resistance due to poor perfusion to target tissues).
- IV furosemide has a very early vasodilatory effect