Before starting

Required

• Baseline
  • Blood pressure
  • Electrolytes
  • Serum creatinine (for creatinine clearance)

Consider

• Baseline
  • Liver function tests · if hepatic impairment suspected

After started or dose changed

Required

• After 1-2 weeks; or after 5-7 days in high risk patients
  • Blood pressure
  • Electrolytes
  • Serum creatinine (for creatinine clearance)

High risk patients

High risk patients include:

• existing chronic kidney disease (stage 3 or higher)
• aged 60 years or over
• with relevant comorbidities such as diabetes mellitus or peripheral arterial disease.
• prescribed a combination of a diuretic plus an angiotensin-converting enzyme (ACE) inhibitor, an angiotensin-II receptor blocker (ARB), or an aldosterone antagonist

Ongoing once stable

Required

• 6 monthly
  • Electrolytes
  • Serum creatinine (for creatinine clearance)

Abnormal results

Renal function

Take appropriate action dependent on renal function monitoring.

Serum creatinine level increase of more than 20%, or eGFR falls more than 15%

Re-measure renal function within 2 weeks.

Serum creatinine level increase of 30 to 50%, or value greater than 200 micromol/L, or eGFR less than 30 mL/min/1.73 m²

Ensure prompt clinical review of volume status. Reduce dose or stop if patient hypovolaemic. Re-measure renal function within 1 week.

Serum creatinine level increase of more than 50%, or value greater than 256 micromol/L, or eGFR approximately 20 to 25 mL/min/1.73 m²

Assess volume status and respond:

• if patient hypovolaemic, stop furosemide
• if patient not hypovolaemic then:
  • check blood pressure
  • review other renal function tests, including electrolytes and proteinuria
  • review other medications to identify nephrotoxic agents

If any uncertainty, seek specialist advice urgently.

Potassium level

Take appropriate action if hypokalaemia occurs.

Level decreases to less than 3 mmol/L (or 4 mmol/L in people at high-risk of cardiac arrhythmias)

Review the diuretic treatment dose or consider stopping it.

Level decreases to less than 2.5 mmol/L (or 3.5 mmol/L in people at high-risk cardiac arrhythmias)

Seek specialist advice urgently.

People at high-risk of cardiac arrhythmias

Includes:

• the elderly
• prescribed digoxin or medicines that prolong the QT interval, such as amiodarone
• paroxysmal arrhythmias, unstable angina or chronic liver disease

Sodium level

Take appropriate action if hyponatraemia occurs.

Level decreases to less than 135 mmol/L

If volume depleted, reduce dose or stop if possible. Consider specialist advice.

Notes

Lipids

Serum cholesterol and triglycerides may rise but usually return to normal within 6 months of starting furosemide.

Diabetes

Use furosemide with caution in patients with diabetes as it can exacerbate diabetes, but hyperglycaemia less likely than with thiazides.

Fluid loss if acutely unwell

If patients develop diarrhoea and vomiting while on furosemide treatment, they should maintain their fluid intake and stop furosemide for 1 to 2 days until they recover. If symptoms persist beyond 2 days, renal function should be checked.

Bibliography

• Ipca Laboratories UK Ltd. Summary of Product Characteristics – Furosemide Tablets BP 20mg. Last revised 21/07/2023 [cited 29/01/2025]
• NICE Clinical Knowledge Summaries (CKS). Heart-failure – Chronic. Updated August 2024 [cited 29/01/2025]
• Hazell T. patient.info. Professional articles: Diuretics. Last edited 23 December 2022 [cited 29/01/2025]
• ESC (2021) 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure. European Heart Journal 42(36), 3599-3726. [cited 29/01/2025]
• Think Kidneys Board. “Sick day” guidance in patients at risk of Acute Kidney Injury: Position Statement from the Think Kidneys Board. Jan 2018 [cited 29/01/2025]
• Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press [cited 06/02/2025]

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