Medical Stone Prophylaxis is also known as Medical Stone Prevention. It is possible to reduce the likelihood of kidney stone formation with the use of medicines. Only medicines can actually change the chemical composition of urine significantly. Although drinking plenty of fluids and modifying dietary intake are both effective, for some patients this is insufficient and consideration is given to taking medicines.
Medical therapy for stone prophylaxis (prevention) is not used for the majority of patients as many people will only make a single stone or a few stones in their entire life and taking medicines is simply not worth it for such individuals. Medical stone prevention is suitable for:
- Recurrent stone formers.
- Patients who present with numerous stones.
- Patients who continue to make stones despite fluid / dietary modification.
- Patients who have required a few surgical interventions.
- Patients who cannot tolerate recurrent stone.
- Frequent travellers.
- People living in remote areas.
- Patients who tolerate anaesthetics poorly.
Not all patients are willing to have medical therapy to avoid future stones. This therapy requires a long-term commitment, as medications need to be taken indefinitely. There is little use staying on these medications for only a few months, as they are only effective when they are taken for years. Many individuals cannot be bothered and do not wish to take tablets for ever, which is perfectly understandable.
Medical stone prophylaxis requires a careful Extensive Metabolic Evaluation which includes at least two 24-hour urine collections, blood tests, stone analysis and imaging of the kidneys. Following these detailed investigations, patients are commenced on medications. The type of medication patients are given depends on the biochemical abnormalities detected in the urine and the composition of the kidney stones. The 24-hour urine tests then need to be repeated to make sure the medicines are doing their job properly by changing the chemical composition of the urine. This is all a big commitment and a nuisance for all but a small proportion of recurrent stone formers.
Choice of Medication
The exact medication used to prevent stone formation depends on a person’s urinary chemistry and the results of chemical analysis of the stone. This is a list of some of the medications used and the type of abnormalities they are designed to correct.
- Thiazide Diuretics e.g. hydrochlorothiazide.
This medication is used for patients who have an abnormally high level of urinary calcium (hypercalciuria) and evidence of calcium stone formation. It has been proven to effective in many clinical trials. Side effects are uncommon but can include fatigue and biochemical abnormalities. Patients taking this medication require blood tests a couple of times a year to make sure their potassium levels are not too high.
- Potassium Citrate e.g. Urocit-K.
This medication is used in patients who have been found to have a low urinary citrate level. Citrate is an inhibitor of stone formation and low levels of citrate have been shown to increase stone recurrence. This is largely used for patients who form calcium stones but is also proven in patients who make Uric Acid stones associated with an acidic urine. This medication is very good at making urine more alkaline (less acidic) which is useful for most Uric Acid and Cystine stones. Interestingly, Potassium Citrate has also been shown to be effective in patients where no specific biochemical abnormality has been detected on urinary testing. Side effects are uncommon and include nausea, vomiting and diarrhoea.
- Allopurinol e.g. Zylopim.
Allopurinol reduces blood and urinary levels of Uric Acid. Interestingly, most patients with Uric Acid stones do not have high urinary levels of Uric Acid and do not require Allopurinol. This medication should be used in patients who have either calcium or Uric Acid stones where there is proven hyperuricosuria (high levels of Uric Acid in the urine). Side effects are uncommon but some patients may be allergic to Allopurinol.
- Thiol medications e.g. Tiopronin.
This drug binds to Cystine in the urine and may be used in patients who form Cystine stones. These stones are very uncommon. Thiols are usually used in combination with Potassium Citrate which is the first line treatment for such calculi.
- Acetohydroxamic Acid (AHA).
This rarely used medication is used in patients with severe recurrent infection related kidney stones. Ideally these stones need to be completely removed surgically, but if this is not possible, the above medication may be used to slow down further infection stone recurrence.