Citric acid

How it works

It acts as a buffering agent and, depending on the salt with which it is combined, modifies urinary pH; as a chelating irrigation it helps dissolve calcium and struvite deposits.

Prescribing in practice

• Confirm the intended preparation and indication, as citric acid appears in many different formulations (oral acidifying mixtures, alkalinising citrate salts, and bladder irrigations) that are not interchangeable.
• Oral citrate combinations contain sodium or potassium and should be used cautiously where there is cardiac, renal or electrolyte concern; check the SPC for the specific product.
• Avoid concomitant use that would inappropriately alter urinary pH against the therapeutic aim and review interacting medicines whose elimination is pH-dependent.

Monitoring

Monitor urinary pH where the aim is to acidify or alkalinise, and check serum electrolytes when sodium- or potassium-containing citrate preparations are used.

Counselling the patient

• Take oral preparations diluted in water as directed.
• Report any swelling, breathlessness or palpitations promptly.
• Use the specific product prescribed and do not substitute.

Evidence & guidelines

Use is long established and reflected in current prescribing references and the relevant SPCs rather than in large randomised trials.