01Principles and purposeThe professional or clinical skill and the decisions it supports.
Prevention reduces the urinary conditions that favour crystallisation and addresses the reason a stone formed. The starting information is the recovered composition, recurrence history, residual burden and a reliable metabolic profile where indicated. A patient with low urine volume and normal calcium excretion may need a different emphasis from one with persistent hypercalciuria, hypocitraturia or acidic urine. Giving several drugs because the patient has had several stones obscures whether each drug has a target and a measurable benefit.
Fluid advice should connect intake with urine output and practical habits. NICE’s adult advice is 2.5–3 litres of water daily; EAU’s strong recommendation is enough fluid, preferably water, to produce more than 2.5 litres of urine in twenty four hours. Additional losses through heat, activity or diarrhoea can make the required intake vary. Spread drinking across the day and consider periods of low intake, but individualise the prescription in heart failure or impaired water handling rather than forcing a standard volume.
Keep dietary calcium normal. NICE gives an adult range 700–1200 mg/day and advises salt no more than 6 g/day; EAU generally uses calcium 1–1.2 g/day and salt 4–5 g/day. These are source-specific ranges, not instructions to eliminate dairy or convert grams of salt into the same grams of elemental sodium. Reduce excessive animal protein and selected high-oxalate exposure when the measured pattern supports it. In enteric hyperoxaluria, calcium with food can help bind oxalate, so blanket calcium restriction can work against prevention.
Drug treatment follows persistent risk and shared decision-making. Citrate can restore an inhibitor of calcium crystallisation and alkalinise urine; thiazide or thiazide-like therapy lowers urinary calcium; allopurinol reduces urate production when hyperuricosuria is relevant. Lowering a laboratory risk factor is not equivalent to proven prevention in every population. NOSTONE found no substantial recurrence difference between hydrochlorothiazide 12.5–50 mg daily and placebo and no dose-response relationship for its primary outcome, with more selected adverse events. NICE and EAU still support selected phenotype-based treatment; discuss uncertainty and do not claim that indapamide was tested by that hydrochlorothiazide trial.
Key points
- For adults, NICE advises 2.5–3 L water daily, salt no more than 6 g/day and normal calcium intake 700–1200 mg/day. EAU uses a 4–5 g/day salt target and recommends enough fluid to achieve urine volume above 2.5 L/day; tailor intake when heart or kidney disease limits fluid.
- Match prevention to the phenotype: consider potassium citrate for recurrent predominantly calcium-oxalate stones, particularly with hypocitraturia; consider a thiazide for recurrent calcium-oxalate disease with hypercalciuria after salt reduction, and allopurinol for appropriate hyperuricosuria.
- Prevention is monitored treatment, not a promise of no further stones. Check formulation-specific contraindications, baseline renal function and electrolytes, early drug safety and a repeat 24-hour urine profile eight to twelve weeks after pharmacological prevention begins.
- The selected citrate mixture contains 1.5 g/5 mL. The local SW London off-label stone schedule starts 10 mL twice daily, but its numerical renal thresholds do not override this selected product’s contraindication in renal dysfunction.
- Uric-acid prevention and active dissolution have different pH objectives. EAU’s prevention figure uses 6.2–6.8; its oral-chemolysis text uses 7.0–7.2 under close supervision. Excess alkalinisation can promote calcium-phosphate stones.
- Infection stones need the most complete feasible clearance, culture-directed management of persistent bacteriuria and residual surveillance. The postoperative antibiotic duration is not established as one universal course.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Recurrent stones containing more than 50% calcium oxalate meet the NICE consideration for potassium citrate; low urinary citrate strengthens the physiological target. Review potassium, renal and cardiac disease, current alkalinisers and medicines that raise potassium. A calcium-phosphate component makes urine-pH monitoring particularly important.
Confirm reliable hypercalciuria after dietary salt reduction, with serum calcium and a systemic-cause assessment. Hyperparathyroidism and RTA need their own management. Before a thiazide-like medicine, identify low sodium or potassium, gout, hypotension, renal or hepatic impairment and relevant interacting drugs.
A low urine pH can drive pure uric-acid stones even without hyperuricosuria. This makes alkalinisation the central biochemical action for that pattern. Allopurinol is appropriate when excess urate excretion contributes; it is not a substitute for correcting persistent acidity in every uric-acid stone former.
Struvite or a mixed infection stone signals a high-risk pathway. Persistent bacteriuria, retained fragments, impaired emptying or a foreign body can sustain recurrence. Distinguish ammonium urate from pure uric acid before changing urine pH, and identify whether a structural source remains.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Baseline phenotype and safety tests - Why
- Choose a targeted medicine and establish whether it can be prescribed safely.
- Interpretation and limitations
- Review stone analysis, serum calcium, potassium, sodium and renal function, with hepatic tests and other drug-specific measures where needed. Use appropriate 24-hour urine calcium, citrate, oxalate, urate, sodium, pH and volume. An unverified numerical renal cutoff from another formulation must not replace the selected product’s restriction.
- 02
Early drug safety review - Why
- Detect electrolyte or blood-pressure harm before a routine efficacy visit.
- Interpretation and limitations
- The selected indapamide SmPC requires potassium measurement during the first week and sodium before treatment and regularly thereafter. Potassium citrate needs renal and potassium surveillance under the initiating service; the cited local protocol retains specialist care for at least eight weeks. Allopurinol requires symptom vigilance as well as renal, hepatic and haematological assessment according to risk.
- 03
Repeat 24-hour urine profile - Why
- Determine whether the intended biochemical change occurred.
- Interpretation and limitations
- EAU suggests the first repeat collection eight to twelve weeks after pharmacological prevention starts. Compare volume and targeted excretion with baseline, review adherence and adverse effects, then adjust a specific intervention. Once urinary parameters normalise, annual collection is suggested, acknowledging limited evidence for the exact interval.
- 04
Imaging and cultures during follow-up - Why
- Detect recurrent or residual disease without unnecessary repeated CT.
- Interpretation and limitations
- Use ultrasound and/or plain imaging according to stone visibility and clinical risk; reserve CT for symptoms or planning where it answers a necessary question. EAU recommends offering further treatment for residual fragments above 4 mm. In infection-stone disease, culture and residual clearance are part of the prevention assessment rather than separate paperwork.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked caseTreat measured hypocitraturia and verify the responseA fifty year old woman has recurrent stones containing 70% calcium oxalate and low citrate in two stable 24-hour collections.+
- 1Her daily urine volume is 1.6 L and citrate 1.2 mmol/day, with normal serum calcium, potassium 4.2 mmol/L and normal renal function. The clinician reviews food, fluids and interacting medicines. She agrees practical measures to increase water intake and reduce salt while maintaining normal dietary calcium, with output and tolerability reviewed rather than an unmeasured instruction to drink more.
- 2The stone specialist selects the local SW London off-label potassium-citrate-mixture schedule:10 mL orally twice daily, using the chosen 1.5 g/5 mL product, so each dose contains 3 g potassium citrate. She shakes and dilutes the mixture and takes it after food. Renal dysfunction, hyperkalaemia, ventricular arrhythmia and Addison’s disease are excluded, and the prescription includes potassium/renal monitoring and illness advice; the licensed cystitis dose is not silently transferred into long-term stone prevention.
- 3The initiating team checks tolerance and blood results during its initial eight-week responsibility period. She reports no gastrointestinal intolerance; potassium is 4.4 mmol/L and renal function remains normal. At twelve weeks, repeat urine volume is 2.6 L/day and citrate 2.5 mmol/day. The team reviews urine pH alongside those improvements to avoid unnecessary excess alkalinisation.
- 4The recorded response supports continuing the agreed dose and habits with an owned monitoring plan. At the supplied six-month review she has had no symptomatic recurrence, but the clinician explains that this observation does not prove permanent protection. Future urine tests, imaging and prescribing review remain matched to her risk and any new symptoms.
02Hypercalciuria persistsConsider a monitored thiazide-like prescriptionAn adult has recurrent predominantly calcium-oxalate stones and persistent high urinary calcium despite verified salt reduction.+
- 1Exclude a systemic cause and review baseline pressure, sodium, potassium, calcium, renal and liver function. Explain that reduced urinary calcium is the treatment target and that recurrence benefit is uncertain for an individual. If the selected specialist option is indapamide, EAU’s calcium-oxalate algorithm includes 2.5 mg/day; the chosen immediate-release 2.5 mg tablet is licensed for hypertension, so the stone use is off-label.
- 2Start 2.5 mg orally in the morning only when the patient has no listed contraindication and normal or minimally impaired renal function. Do not substitute a 1.5 mg modified-release product as an assumed equivalent stone regimen or increase above 2.5 mg/day from the selected product schedule. Arrange potassium during the first week and regular sodium, renal and blood-pressure review.
- 3At follow-up, compare urine calcium and citrate, symptoms and safety results before continuing. Stop and reassess important electrolyte disturbance, increasing renal insufficiency or hepatic encephalopathy. If the risk factor does not improve or harms outweigh the possible benefit, reconsider the treatment instead of adding several agents without a clear target.
03Uric-acid prevention differs from dissolutionChoose the pH objective and urate treatment deliberatelyA patient has confirmed uric-acid stones and persistently acidic urine.+
- 1Clarify whether the aim is preventing a future stone or dissolving an existing one. EAU’s metabolic prevention figure gives urine pH6.2–6.8; the separate oral-chemolysis text gives 7.0–7.2 for active dissolution, while its metabolic figure shows a broader dissolution range. Use a stated supervised plan and fresh home urine-pH measurements, not a merged universal target. Rising pH can favour calcium-phosphate crystallisation.
- 2Choose an alkaliniser and formulation appropriate to renal function, potassium and interacting medicines, and titrate to the assigned pH with specialist review. For obstruction, ensure drainage and safety assessment rather than relying on dissolution to rescue a threatened kidney. Follow actual stone burden during dissolution and reconsider intervention when required.
- 3When hyperuricosuria is present and dietary measures are insufficient, an appropriate adult allopurinol plan can start 100 mg orally daily after food and be adjusted to urine and serum urate and organ function. It does not replace the pH intervention when acid urine remains the main driver. Do not apply this pure uric-acid plan to ammonium urate without re-evaluating its infection and nutritional context.
04Prevent recurrent infection stonesAddress stone material and the infectious environmentStone analysis identifies struvite or a mixed infection stone.+
- 1Arrange the most complete feasible removal of stone material and evaluate urine cultures, drainage, bladder function and foreign bodies. Treat persistent bacteriuria with a culture-directed specialist antibiotic plan. The evidence does not supply one fixed postoperative duration that can be prescribed to every infection-stone patient.
- 2After removal and infection control, investigate metabolic abnormalities where a mixed stone suggests an underlying calcium-stone mechanism. General fluid and dietary measures remain relevant, but they do not sterilise a retained infected stone or correct an obstructed urinary system.
- 3Review residual fragments and surveillance imaging with the patient. A fragment above 4 mm usually warrants an offer of further treatment under EAU guidance; if observation is chosen, document the reason and close follow-up. A new febrile obstructed episode returns to emergency drainage assessment regardless of the prevention prescription.
05Relevant medicines and safetySpecific regimens and precautions when the skill involves prescribing.
Potassium citrate mixture 1.5 g/5 mL, selected Thornton and Ross product
Selected SW London specialist stone-prevention schedule, off-label:10 mL orally twice daily, equivalent to 3 g per dose and 6 g/day of this product. Shake, dilute well with water and take after meals. Review and individualise to biochemical response and tolerance; the specialist retains care for at least 8 weeks under that local protocol. This is long-term reviewed prevention, not a short cystitis course.The selected SmPC contraindicates renal dysfunction, hyperkalaemia, ventricular arrhythmias and Addison’s disease; do not reinterpret the local protocol’s eGFR thresholds as permission to ignore these product restrictions. The worked patient has normal renal function. Check potassium/renal function and review potassium supplements, potassium-sparing diuretics, ACE inhibitors, ciclosporin and aliskiren; cardiac glycosides also need review. Urinary alkalinisation reduces activity of nitrofurantoin and methenamine. Monitor pH to avoid excess alkalinisation and calcium-phosphate risk. Gastrointestinal irritation may limit use. The mixture contains sucrose and is unsuitable in the stated hereditary fructose/glucose-galactose/sucrase-isomaltase disorders. Under the local illness advice, withhold during acute gastroenteritis and restart only after 24–48 hours of recovery with normal eating/drinking and an appropriate safety assessment. Long-term stone use in pregnancy is not established by the short-term cystitis label.
Indapamide 2.5 mg immediate-release tablets, selected Strides product
Specialist-selected off-label stone prevention for persistent hypercalciuria:2.5 mg orally once daily in the morning, as included in the EAU calcium-oxalate algorithm. Do not exceed 2.5 mg/day under this selected product schedule or assume interchangeability with 1.5 mg modified-release tablets. Review early safety and urine response at 8–12 weeks; continuation depends on benefit and tolerance.Contraindicated in severe renal failure, including CrCl below 30 mL/min, severe hepatic impairment or hepatic encephalopathy, hypokalaemia, hyponatraemia or hypercalcaemia, porphyria, Addison’s disease and relevant sulfonamide/product hypersensitivity. Use only when renal function is normal or minimally impaired; review exact renal assessment in older people. Measure sodium before starting and regularly, potassium during the first week and more often if at risk; follow magnesium, renal function, pressure, glucose and urate as appropriate. Correct electrolyte disturbance and stop for increasing renal insufficiency or hepatic encephalopathy. Avoid routine lithium combination; check QT-prolonging drugs, digoxin, ACE inhibitors, NSAIDs and other potassium-lowering drugs. Acute eye pain or visual loss needs immediate cessation and urgent assessment for angle closure; stop for photosensitivity and assess. Avoid during pregnancy and do not use while breastfeeding. Do not use this lactose/sucrose-containing product in the listed hereditary galactose or fructose intolerance, total lactase deficiency, glucose-galactose malabsorption or sucrase-isomaltase insufficiency.
Allopurinol 100 mg tablets, selected Flamingo product
For an appropriate adult hyperuricosuric stone phenotype, start 100 mg orally once daily after a meal. EAU stone regimens use 100–300 mg/day, adjusted to urinary and serum urate and tolerance; do not start at the upper dose. Severe renal impairment can require less than 100 mg/day or 100 mg at intervals longer than one day, and hepatic impairment needs a reduced individual dose. Review long-term rather than prescribe a fixed short course.Do not use with product hypersensitivity. Stop immediately and obtain urgent assessment for rash or systemic hypersensitivity; never rechallenge after DRESS, SJS or TEN. Consider HLA-B*5801 testing before initiation in high-prevalence groups, including people of Han Chinese, Thai or Korean ancestry; a known carrier should not start unless no reasonable alternative exists and specialist benefit exceeds risk. CKD and thiazides increase hypersensitivity risk. Avoid azathioprine or 6-mercaptopurine coadministration; if specialist co-use is essential, reduce that thiopurine to 25% of its usual dose with frequent blood-count monitoring. Review warfarin/INR, theophylline, ciclosporin, ACE inhibitors and other interactions; separate aluminium hydroxide by at least 3 hours. Monitor renal and hepatic function and urate; early hepatic tests are advised in liver impairment. The selected label advises delaying initiation until an acute gout attack subsides, while established treatment continues during a treated flare. Pregnancy requires no safer alternative and a compelling risk-benefit assessment; breastfeeding is not recommended. Do not use this lactose-containing product in hereditary galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption.
06Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- Record a baseline and follow-up for the abnormality each drug addresses, including fluid output, urine citrate or calcium or urate, pH and the patient’s ability to sustain the plan.
- Keep early medicine-safety checks separate from the eight-to-twelve-week efficacy collection; dangerous potassium or sodium changes should not await a routine metabolic appointment.
- Review new medicines, acute illnesses, falls, skin reactions, eye symptoms and changes in renal or liver function before renewing long-term treatment.
- Count symptomatic events and follow residual disease with proportionate imaging. A normalised urine parameter and a quiet few months support assessment but do not establish permanent stone freedom.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Product restrictions and protocol thresholds differ
A local service may describe how it monitors a class of alkalinisers across renal-function ranges. A particular licensed mixture can have a broader contraindication. Select a compatible product and patient instead of using the local number to erase the label’s restriction.
Do not convert grams into unverified equivalents
The selected mixture’s 1.5 g/5 mL concentration makes 10 mL equal 3 g potassium citrate. This calculation does not establish the same millimoles of citrate or potassium as every tablet or alternative salt, so substitutions need their own formulation check.
Lower calciuria is not a guaranteed clinical endpoint
The NOSTONE hydrochlorothiazide findings strengthen the need to discuss uncertainty and adverse effects. They neither demonstrate that indapamide is effective for every patient nor directly test that different agent; continue phenotype-based assessment and measure actual outcomes.
Infection control needs a physical endpoint
Persistent infected stone material can sustain bacteriuria. A long antibiotic prescription without a clearance and drainage assessment may suppress a symptom while leaving the main recurrence mechanism in place.
08Common pitfallsFrequent interpretation and management errors.
- 01
Restricting calcium broadly or confusing grams of salt with grams of sodium can undermine otherwise reasonable dietary advice.
- 02
Using an unqualified renal cutoff from a local citrate protocol can conflict with the selected product’s contraindication in renal dysfunction.
- 03
Escalating alkali without reviewing the intended prevention or dissolution pH can increase calcium-phosphate risk.
- 04
Interpreting thiazide-induced improvement in a urine test as proof that recurrence is prevented can hide both uncertainty and drug harm.