ACTIONS. These are the 'transport-inhibiting diuretics
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1. Diuretics increase the volume of urine passed Commonly prescribed diuretics include:
thiazides (bendroflumethiazide/ bendrofluazide, chlortalidone,indapamide)
loop diuretics (furosemide/frusemide, bumetanide)
potassium-sparing diuretics (amiloride, triamterene)
2. ACTIONS These are the 'transport-inhibiting diuretics‘ because they block the enzymes which reabsorb electrolytes (sodium, potassium and chloride) from urine into the circulation.
As electrolytes are lost in the urine, water is lost with them. This doesn't work so well if the patient takes a high salt diet or smokes.
Diuretics also dilate blood vessels.
3. INDICATIONS Diuretics are prescribed when the body contains too much
fluid, in conditions associated with oedema and hypertension.
long-term: hypertension, heart failure, oedema
acute therapy: pulmonary oedema, renal failure;
long term: heart failure, occasionally hypertension
Potassium-sparing diuretics are prescribed with other diuretics to reduce potassium loss.
4. ADMINISTRATION AND DOSES Oral administration should be linked to meal-times. In some patients, food reduces furosemide-induced diuresis by up to 66%.
If heart failure worsens, absorption may decrease, making the diuretic less effective.
6. ADMINISTRATION: furosemide
Oral furosemide induces diuresis within 1 hour and continues to do so for 6 hours.
Administration <6 hours before bedtime may disturb sleep.
Discuss with patient the most convenient time for administration and suggest flexibility to accommodate social engagements.
Usual dose is 20-40mg, but this may be increased if oedema cannot be controlled any other way.
Intravenous furosemide acts within 20-60 minutes.
Rapid administration (>4mg./minute) risks damage to hearing and balance.
7. Elderly patients receive lower initial
doses, which are subsequently
adjusted according to renal
(serum creatine, urea, glomerular filtration rate (GFR), urinalysis).
22. Cautions and contra-indications include: Previous hypersensitivity responses. People allergic to sulphonamides may be allergic to thiazides and furosemide.
Impaired renal function. Most thiazides are ineffective in renal failure (GFR<20ml./min.). Contra-indicated if GFR<10 ml./min.
Impaired liver function. Diuretics increase potassium and magnesium loss and may precipitate coma.
Pre-existing fluid and electrolyte imbalances will be intensified.
Exacerbation of: Addison's disease, gout, diabetes, lupus, porhyria
Potassium-sparing diuretics are not recommended in severe, acute illness, renal failure or pregnancy.
Pregnancy. Diuretics jeopardise the blood supply to the placenta. Used only under specialist supervision. Furosemide may cause severe respiratory problems in the neonate.
Lactation. Diuretics impair formation of breast milk.
23. Interactions include Some drugs accentuate the adverse effects of diuretics:
Hypotension: all anti-hypertensives, general anaesthetics, alcohol, benzodiazepines, phenothiazines, anti-depressants, nitrates
Loss of sodium: carbamazepine, aminoglutethimide
Loss of potassium: digoxin, corticosteroids, bronchodilators, amphetamines, reboxetine, terfanadine, 'cold cures', liquorice.
Cardiac arrhythmia due to hypokalaemia: amisulpride, pimozide, sertindole, terfanidine, thioridazine, sotalol
Dangerously high potassium concentrations may occur if potassium-sparing diuretics are co-administered with: any potassium-rich food, herbal preparations or supplements, ciclosporin, NSAIDs (non-steroidal anti-inflammatory drugs), ACE inhibitors, tacrolimus, oestrogen and progestogens
Organ damage may occur if diuretics are combined with certain drugs:
NSAIDs, cisplatin, cephalosporins affect: kidney
amiodarone, anti-arrhythmics affect: heart
aminoglycosides, vancomycin affect: ear
Diuretics cause lithium, quinidine and amphetamines to accumulate.
Diuretics can be rendered ineffective by: corticosteroids, oestrogens, NSAIDs.
25. HYPOKALAEMIA - revision DEPRESSION,
HR slows, AV BLOCK,
HEART SIZE ?