- There is also a secondary effect – loop diuretics cause the concentration of sodium and chloride to be higher in the DCT than they are normally. This means when the tubular fluid passes the juxtamedually apparatus, the apparatus thinks that BP is high, and thus renin is not secreted. This means that there is NOT much vasoconstriction of the efferent arteriole, and there is vasoconstriction of the afferent arteriole. (this is a bit counter intuitive for the drug, but doesn’t seem to have too much effect).
Loop diuretics e.g. furosemide (aka frusemide), bumetanide
- Can cause excessive salt and water loss, and thus lead to renal impairment and hypotension.
- Can cause hyponatremia as a result of excessive sodium loss. This effect is exaggerated because the body will produce ADH in response to loop diuretics, resulting in water retention, despite the sodium loss, and thus the blood becomes ‘diluted’ with too little sodium.
- Can cause hypokalaemia
- Hypomagnesia – which may lead to arrhythmia
- Can cause ototoxicity resulting in damage to the cochlear fluid. This is rare, and tends to occur in renal failure, where the drug is not excreted quickly enough.
- Can cause incontinence due to rapid loss of large amounts of fluid. In some older men with BPH, this can cause retention.
- Hypomagnesaemia and hypocalcaemia
- Can precipitate gout – due to induction of hyperuraemia – particularly in patients with a past history of gout. Urate levels should be monitored in these patients and allopurinol may need to be titrated up accordingly. Gout is unusual with loop diuretics and much more common with thiazide diuretics.
- Tolerance may sometimes occur to due hypertrophy of the tubular epithelium at the site of action of the drug
Indications and Uses
- Heart failure
- Liver failure / cirrhosis
- Renal impairment
- A typical dose of frusemide is 40mg daily
- Up to 120mg daily (often in divided doses) is not unusual
- IV dose is the same as the oral dose (although IV is probably more effective, due to additional venodilation effects, and variable oral absorption)
- 40mg frusemide is equivalent to 1mg budesonide
- Australian Medicines Handbook - Frusemide
- Waller, DG., Renwick AG., Hillier K. (2005). Medical Pharmacology and Therapeutics. 2nd ed. Elsevier Saunders