Potassium Replacement

Potassium replacement treats hypokalaemia (serum potassium under 3.5 mmol/L). It is one of the commonest hospital prescriptions and one of the most dangerous when prescribed or given carelessly. Moderate hypokalaemia (2.5 to 3.0 mmol/L) can cause weakness, ileus and arrhythmia, and severe hypokalaemia (under 2.5 mmol/L) can cause paralysis and cardiac arrest.

Mechanism. Potassium moves across cell membranes and sets the resting electrical state of nerve, muscle and heart cells. Replacement raises extracellular potassium, restores membrane potential and removes arrhythmia risk.

Pharmacokinetics. Oral potassium is absorbed quickly, though modified release forms take hours. About 98% of body potassium is inside cells, so the serum level falls by about 0.3 mmol/L for each 100 mmol deficit. Insulin, salbutamol and alkalosis push potassium into cells and lower the serum level.

Intravenous rates.

• Peripheral line: no more than 40 mmol/L, up to 10 mmol/hour.
• Severe hypokalaemia with arrhythmia or paralysis: up to 20 mmol/hour or more by central line, with continuous ECG monitoring and in a high dependency setting.
• Total in any 24 hours is usually 80 to 120 mmol, adjusted to levels.

Estimating dose. Levels are an imperfect guide to total deficit, so recheck after each 40 to 60 mmol.

• First-line. Oral potassium chloride for mild to moderate hypokalaemia in people who can swallow and absorb.
• Alternative. Potassium-sparing diuretics or dietary potassium for chronic loss; potassium citrate when acidosis coexists.
• Specialist. Hypokalaemic periodic paralysis (small doses, rebound risk), renal tubular acidosis, primary aldosteronism (spironolactone), Gitelman and Bartter syndromes.
• Emergency. Hypokalaemia with ECG changes, arrhythmia, respiratory muscle weakness or digoxin toxicity.

Selection. Use oral replacement when possible. Add magnesium when potassium does not rise. Use intravenous replacement only when symptoms are severe or the gut is not working.

Contraindications. Hyperkalaemia; severe kidney failure with oliguria; untreated adrenal insufficiency; tablets in oesophageal obstruction or severe gut slowing.

Serious adverse effects.

• Hyperkalaemia with arrhythmia and arrest, particularly with kidney impairment.
• Pain and phlebitis at the infusion site; tissue damage on extravasation.
• Gut ulcers and strictures from tablets.
• Nausea, vomiting and diarrhoea.

Major interactions. ACE inhibitors, ARBs, spironolactone, eplerenone, amiloride, triamterene, trimethoprim, ciclosporin, tacrolimus and NSAIDs raise potassium; insulin, salbutamol and loop or thiazide diuretics lower it.

Common prescribing errors.

• Giving concentrated potassium as a bolus or pushing it into a line.
• Running potassium faster than the labelled rate.
• Prescribing in oliguria without a plan to recheck.
• Treating potassium alone when magnesium is low.
• Continuing replacement after the cause has resolved.

Special groups.

• Pregnancy: replace with the usual adult doses; correct hyperemesis losses.
• Breastfeeding: compatible.
• Children: weight-based; oral route preferred.
• Older adults: frequent check-ups; often on interacting drugs.
• Kidney: halve the dose and recheck within hours; avoid in oliguria.
• Liver: monitor with diuretics and spironolactone.
• East Africa: premixed potassium bags may be unavailable, and ampoules of concentrated potassium chloride are a known source of fatal errors, so store them away from sodium chloride and water and dilute under a written local procedure; diarrhoeal losses, malnutrition and diuretic use are common causes.

Monitoring. Serum potassium 4 to 6 hours after dose changes; ECG with intravenous replacement and with levels under 2.5 mmol/L; magnesium, creatinine and glucose.

Referral and escalation. ECG changes, paralysis, failure to correct, or need for central venous infusion.

Comparison with alternative classes. Potassium chloride corrects deficit fastest. Potassium-sparing diuretics prevent loss with less pill burden but risk hyperkalaemia, and dietary measures are too slow for significant deficit.