Alkaline citrate in prevention of recurrent calcium oxalate stones.

Calcium oxalate (CaOx) is the most common constituent of calcium renal stones, often mixed with calcium phosphate (CaP). The recurrence rate of these stones is high and their aetiology complex. Despite new effective, less invasive methods to remove the stones, preventive treatment is often necessary to avoid recurrence. Alkaline citrate is a relatively new medical treatment reported to give a stone free rate of between 67-92 per cent in long term studies with three daily doses. The present investigation was undertaken in order to study further the risk factors in CaOx stone formation, the influence and usefulness of a single evening dose of alkaline citrate, and the value of a four hour morning urine sample in the evaluation of patients who form stones. The highest CaOx crystallisation risk (CaOx-CR) in whole urine was recorded in the pH range 4.5-5.5, with lower values above this pH. Between pH 6.5-7.5 the number of small CaP crystals was considerably increased. The crystallisation of CaOx on hydroxyapatite (HAP) was inhibited for four hours by 1 and 2% whole urine or citrate in concentrations of 1% that in normal urine. The formation of CaP crystals in a supersaturated system was considerably reduced when citrate concentrations exceeded 0.5 mmol/l. The number of medium sized (6.5-14 microns) and large crystals (15.5-27 microns) was reduced, and small crystals (3.5-5 microns) predominated at higher citrate concentrations. The correlation between the composition of 24-h urine samples and 4-h urine specimens collected between 0600-1000, from patients with CaOx stones before and during a course of alkaline citrate given as a single evening dose was good, with the best correlation recorded during treatment. These results suggest that the 4-h urine sample might be adequate for the follow up of patients treated with alkaline citrate. A total amount of 7.5 g of potassium sodium citrate (PSC) in 1, 2, and 3 doses favourably affected urine composition in patients with CaOx stones. Three doses gave the most sustained effect, and a single evening dose gave the most pronounced effect between 2200-0600. Long term treatment (mean +/- SD duration 3.5 +/- 1.7 years) of patients who formed calcium stones with PSC in a single evening dose of 3.75 or 5.0 g (n = 55) gave a stone free rate of 75 per cent, but no clinical effect was apparent when 5.0 or 7.5 g were given in two or three doses (n = 17).(ABSTRACT TRUNCATED AT 400 WORDS)