Infection stones form in the present of alkaline urine (pH > 7.2) and an environment rich in ammonia.
Urease – splits urea into ammonia (NH3) and carbon dioxide.
Ammonia (NH3) + H20 -> Ammonium (NH4) + OH+ = alkaline urine
Ammonium combines with magnesium, phosphate and water to create struvite stones.
(Calcium carbonate apatite stones are alternate infection forms which occur in a similar process).
Urease producing bacteria:
- Proteus (more than half)
- Klebsiella
- Serratia
- Staphylococcus
- Morganella
- Providencia
- Enterobacter
- Ureaplasma
- E.coli, pseudomonas and enterococcus typically do not (0 – 5 %)
Those at high risk of struvite or infection stones – women, elderly, neuropaths, diversions, foreign bodies, anything else causing UTIs.
Treatment:
- Surgical clearance
- Treat UTI (may need extended course)
- Stone prevention advice – fluids, low salt, lifestyle
- UTI prevention and optimise anatomical abnormalities if able
- Acetohydroxamic acid (Lithostat)
- Oral urease inhibitor
- May prevent struvite stone formation in patients unable to have surgical clearance
- 30 % side effects – DVT, tremor, headache, GI upset, palpitations, loss of taste, haemolytic anaemia
- Urinary acidification
- Ammonium chloride 1g BD or TDS
- Methionine 200 – 500 mg OD to TDS