Furosemide — NZ Medication Guide

What is Furosemide?

Furosemide (generic name: furosemide (frusemide)) is a medication used primarily for oedema (fluid retention) associated with heart failure, kidney disease, and liver cirrhosis. Furosemide tablets (20mg, 40mg, 500mg) and oral solution are funded by Pharmac on the Pharmaceutical Schedule without Special Authority.

In New Zealand, furosemide (also known as frusemide) is the first-line loop diuretic for managing fluid overload in heart failure. The Heart Foundation of New Zealand heart failure guidelines recommend furosemide as a cornerstone of symptom management. Patients with chronic heart failure on furosemide should be enrolled in a structured heart failure management programme where available. Regular monitoring of renal function, electrolytes, and weight is essential. Potassium supplementation or co-prescription of a potassium-sparing diuretic may be required.

What is Furosemide Used For?

Furosemide is prescribed by healthcare professionals in New Zealand for the following indications:

• Oedema in congestive heart failure (mild to severe)
• Pulmonary oedema (acute — IV use in hospital)
• Oedema associated with renal disease (nephrotic syndrome)
• Oedema in hepatic (liver) cirrhosis with ascites
• Hypertension (second-line, where thiazides are insufficient)
• Hypercalcaemia management (adjunct, hospital setting)

How Does Furosemide Work?

Furosemide is a potent loop diuretic that acts on the ascending loop of Henle in the kidney, inhibiting the Na-K-2Cl co-transporter. This prevents reabsorption of sodium, potassium, and chloride, leading to a significant increase in urine output (diuresis) and reduction of fluid overload. Its rapid onset makes it valuable in acute fluid emergencies such as pulmonary oedema.

How to Take Furosemide

Take furosemide in the morning (and midday if twice daily) to avoid nighttime urination disturbing sleep. Oral tablets can be taken with or without food. The dose is highly individualised based on the severity of fluid overload and kidney function. Do not adjust your dose without consulting your doctor. Weigh yourself daily if instructed — a rapid gain of more than 2kg in 24–48 hours warrants urgent medical review. Maintain adequate fluid intake unless fluid restricted by your specialist.

Common Side Effects

Like all medications, Furosemide may cause side effects. Common side effects include:

• Increased urination (diuresis) — expected effect
• Hypokalaemia (low potassium) — muscle weakness, cramps
• Dehydration — thirst, dry mouth, dizziness
• Hyponatraemia (low sodium)
• Dizziness on standing (orthostatic hypotension)
• Elevated uric acid — may trigger gout

Serious Side Effects — Seek Medical Attention

Contact your doctor or call 111 immediately if you experience any of the following serious effects:

• Severe electrolyte depletion — dangerous hypokalaemia, hypomagnesaemia
• Acute kidney injury — particularly with dehydration or NSAID use
• Ototoxicity (hearing loss) — rare; risk with high IV doses especially combined with aminoglycosides
• Severe dehydration and hypovolaemia
• Allergic reaction in sulfonamide-sensitive patients (rare — cross-reactivity uncertain)

Drug Interactions

Always inform your prescriber and pharmacist of all medications, supplements, and herbal products you are taking. Notable interactions with Furosemide include:

• ACE inhibitors/ARBs — first-dose hypotension risk; use with caution
• NSAIDs (ibuprofen, naproxen) — reduce diuretic effect and worsen kidney function
• Aminoglycoside antibiotics (gentamicin) — combined ototoxicity risk
• Lithium — furosemide increases lithium retention and toxicity risk
• Digoxin — hypokalaemia caused by furosemide increases digoxin toxicity risk
• Potassium supplements — often co-prescribed; monitor levels

New Zealand Prescribing Information

In New Zealand, furosemide (also known as frusemide) is the first-line loop diuretic for managing fluid overload in heart failure. The Heart Foundation of New Zealand heart failure guidelines recommend furosemide as a cornerstone of symptom management. Patients with chronic heart failure on furosemide should be enrolled in a structured heart failure management programme where available. Regular monitoring of renal function, electrolytes, and weight is essential. Potassium supplementation or co-prescription of a potassium-sparing diuretic may be required.

Frequently Asked Questions

How quickly does furosemide work?

Oral furosemide typically starts working within 30–60 minutes, with peak diuresis occurring 1–2 hours after the dose. The effect lasts approximately 4–6 hours. Intravenous furosemide works within minutes — this is why it is used in hospital emergencies such as acute pulmonary oedema. Your dose may be adjusted by your doctor based on your response and weight changes.

Why do I need to weigh myself daily?

Daily weight is the most sensitive indicator of fluid retention changes. A weight gain of more than 2kg over 1–2 days usually means fluid is accumulating (even before visible ankle swelling appears). Your heart failure team will give you a specific weight threshold to monitor and instructions on when to call for help or adjust your furosemide dose. Always weigh yourself at the same time of day, with the same clothing, and using the same scales.

References & Further Information

The following New Zealand and international resources were used to inform this page:

• New Zealand Formulary — Furosemide
• Pharmac — Funded Medicines Schedule
• Heart Foundation NZ — Heart Failure Guidelines
• BPAC NZ — Heart Failure Management in Primary Care

Reviewed by a Registered Pharmacist — KiwiMeds New Zealand