Furosemide
Furix · Impugan
Inhibits the Na⁺/K⁺/2Cl⁻ transporter in the loop of Henle. The dose–response relationship is a threshold curve, not a line: below the threshold nothing happens, and in renal failure the threshold dose must be raised to achieve any effect at all.
Vigorous diuresis can cause hypovolaemia, renal failure, and severe electrolyte disturbance. Ototoxicity with rapid intravenous administration of high doses.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Acute pulmonary oedema | 40 mg iv (80 mg if the patient is already on furosemide) | effect within 5–15 minutes |
| Chronic heart failure | 20–80 mg orally daily | lowest dose that keeps the patient euvolaemic |
| Renal failure | Double the dose ladder; 80–250 mg iv may be required | threshold dose rises with falling eGFR |
| Diuretic resistance | Continuous infusion, or addition of a thiazide | sequential nephron blockade |
No upper dose limit as such — but the effect requires a higher dose at low eGFR.
Caution in cirrhosis: risk of hepatic encephalopathy and hypokalaemia.
0,5–1 mg/kg iv per dose, maximum 2 mg/kg.
Do not increase the dose when there is no effect without first confirming that the patient is actually fluid-overloaded — in the volume-depleted patient, more furosemide worsens renal function.
Pharmacokinetics
- BIOAVAIL.
- 10–90 % (highly variable)
- Vd
- 0,1–0,2 l/kg
- t½
- 1,5–2 h
- PROTEIN BINDING
- > 95 %
- METABOLISM
- Glucuronidation
- EXCRETION
- Renal, active secretion
- ONSET
- 5 min iv · 30–60 min orally
- DURATION
- 2–6 h