General stone prevention advice
- Increase fluid intake – aiming for 2.5 L urine output / day
- Reduce animal protein in diet
- Increase vegetable and fibre, increase citrus intake
- Reduce salt intake (Na and Ca share transporter in tubules, high salt increases calcium in urine)
- Lose weight if overweight
Hydrochlorothiazide
25 – 50 mg daily.
Mechanism – directly stimulates calcium reabsorption in the distal tubule, reducing calcium levels in urine, and also promotes secretion of sodium.
Indication – hypercalciuria, or recurrent calcium oxalate stones with normal metabolic workup
Problem – can cause hypokalaemia with subsequent intracellular acidosis and hypocitraturia (consider potassium citrate supplementation)
Side effects – thirst, polyuria, cramps, GI upset, occasional sexual/libido changes, photosensitivity with recent reports of increased non melanoma skin cancers
RCT 2023 NEJM – no benefit cf. placebo for calcium oxalate stones
Potassium citrate
Mechanism – Orally ingested citrate salts are metabolised to bicarbonate in the liver – alkali load inhibits citrate reabsorption (and alkalinises the urine).
Slow release tablets may be poorly absorbed especially in patients with malabsorption as primary issue – liquid or powdered forms recommended.
Indication – hypocitraturia, recurrent calcium stones with metabolic abnormality, alkalinisation (including prophylaxis, cystinuria), RTA
Problem – difficult to obtain in Australia, large pill burden for recommended dose, expensive
Side effects – GI upset, diarrhoea, peptic ulcers (esp in renal failure), hyperkalaemia (if using ACE-I)
Sodium bicarbonate
Excellent alkalinising agent. Two tablets (2 x sodibic 840 mg, TDS, between meals)
Indication – alkalinisation (dissolution, cystinuria), hypocitraturia (as alternative to potassium citrate), RTA, (non stone = metabolic acidosis from diversion, alkalinised post ejaculatory urine sample in retrograde ejaculation for sperm retrieval).
Problem – sodium and calcium reabsorption are coupled in the proximal tubule (cf. distal tubule which is where HCT works) – so high sodium load prevents reabsorption of sodium and also calcium, leading to hypercalciuria and potentially calcium stones.
Side effects – GI upset, thirst
Ural – contains 1.75g sodium bicarb, sodium citrate, amongst others – effective alkalinising agent. Reasonable sodium load as well.
Allopurinol
For uric acid stones, the primary determinant is often acidic urine rather than uric acid levels in blood or urine, so alkalinisation is priority. Most useful in those with demonstrable hyperuricaemia or hyperuricosuria.
100 – 300 mg / day. Reduce dose in poor renal function. Start 100 mg / day and titrate up
Mechanism – xanthine oxidase inhibitor (key enzyme in production of uric acid from purine breakdown).
Indication – hyperuricosuria, hyperuricaemia.
Problem – side effects
Side effects – rash, allopurinol hypersensitivity syndrome (progressing to Stevens Johnson), muscle pains, GI upset, gout flare
Febuxostat is an alternate or second line treatment for those who do not tolerate allopurinol.