Before starting

Required

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

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)

Defining high risk patients

High risk patients includes those:

• With existing chronic kidney disease (stage 3 or higher)
• Aged 60 years or over
• With relevant comorbidities such as diabetes mellitus or peripheral arterial disease.
• Taking a combination of a diuretic plus an angiotensin-converting enzyme (ACE) inhibitor, an angiotensin-II receptor antagonist (AIIRA), or an aldosterone antagonist
• Those taking digoxin or drugs that prolong the QT interval (such as amiodarone).
• Those with paroxysmal arrhythmias, unstable angina, or chronic liver disease.

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%; eGFR falls more than 15%

Re-measure renal function within 2 weeks.

Serum creatinine level increase of more than 30-50%, 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; eGFR approximately 20–25 mL/min/1.73 m²

Assess volume status and respond:

• If patient hypovolaemic then 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 dependent on potassium level monitoring.

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

Review the diuretic treatment dose or consider stopping it.

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

Seek specialist advice urgently.

Notes

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 – 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 23/11/2021 [cited 08/08/2023]
• NICE Clinical Knowledge Summaries (CKS). Heart-failure – Chronic. Updated July 2023 [cited 31/07/2020]
• Rull G. Patient. Professional articles, cardiovascular disease. Diuretics. Last edited 30 December 2016 [cited 30/07/2020]

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