Loop diuretics
also: furosemide · bumetanide
Overview
Powerful diuresis for fluid overload — heart failure, pulmonary/peripheral oedema. Not an antihypertensive of choice.
Mechanism
Inhibit the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC2) in the thick ascending limb of the loop of Henle → large natriuresis and loss of the medullary concentration gradient. Also venodilate (early relief in acute pulmonary oedema).
Indications
- Heart failure / fluid overload
- Pulmonary oedema
- Oedema in CKD / nephrotic syndrome
- Resistant hypertension with low eGFR
The agents
oral bioavailability ~50%, variable
IV in acute decompensation.
more reliable oral absorption
Used when gut oedema limits furosemide.
Adverse effects
Opposite of thiazides.
Dose-related, esp. rapid IV + aminoglycosides.
Cautions & contraindications
Worsens hyperuricaemia.
Interactions
- Aminoglycosides → additive ototoxicity + nephrotoxicity
- Hypokalaemia potentiates digoxin
- Lithium retention
Monitoring & kinetics
U&E (Na⁺, K⁺, Mg²⁺), renal function,Weight, fluid balance
Oral or IV. Works even at low eGFR (unlike thiazides) but needs higher doses.
Source: BNF — Loop diuretics