Severe: K⁺ under 2.5 mmol/L, symptoms or ECG changes — IV replacement with cardiac monitoring.
Check and replace magnesium too, or potassium won't stay up.
Act now
- 1
ECG: U waves, flat T waves, ST depression, long QT, arrhythmias. Monitor if severe or on digoxin.
Assess
- Mild 3.0–3.4, moderate 2.5–2.9, severe under 2.5 mmol/L.
- Symptoms: weakness, cramps, palpitations, ileus.
- Causes: diuretics, vomiting, diarrhoea or high-output stoma, refeeding, insulin or salbutamol, steroids, low magnesium.
Investigations
- U&E, magnesium, calcium, phosphate, glucose, venous gas (alkalosis); digoxin level if on it.
Manage
- Mild or moderate and able to swallow: oral potassium; recheck in 24–48 hours.
- Severe, symptomatic, or unable to take oral: IV potassium chloride in a pre-mixed bag.
- Peripheral line: usually no more than 10 mmol/hour and 40 mmol/L; faster or stronger only with cardiac monitoring per local policy.
- Recheck K⁺ after each IV bag. Treat the cause.
Escalate when
- K⁺ under 2.5 mmol/L, arrhythmia, digoxin toxicity, or needing high-rate replacement: senior and HDU.
Doses and prescribing
Potassium chloride (Sando-K)
2 tablets oral 2–3 times daily (12 mmol K⁺ per tablet).
Potassium chloride
40 mmol in 1 L 0.9% sodium chloride IV over at least 4 hours (pre-mixed bag).
Check the BNF and your local formulary before prescribing.
Written to current guidance · sources checked 14 Nov 2026. We watch NICE for updates weekly.
Sources (1)
Reviewed by Aboodee Alhasso, MPharm MRCPharm IP on 14 Nov 2026
For healthcare professionals, as an aid to clinical judgement — not a substitute for it. Follow your local policy and ask a senior when in doubt.