Pentosan polysulfate as an inhibitor of calcium oxalate crystal growth.

Pentosan polysulfate was studied as a calcium oxalate crystal growth inhibitor. The inhibition from pentosan polysulfate at concentrations ranging from 3.5 to 110 mg./l. was measured in simple inorganic calcium oxalate solutions at pH 5, 6 and 7. Pentosan polysulfate also was mixed with urine at concentrations from 10 to 350 mg./l. and inhibition determined. Measurement of calcium oxalate crystal growth inhibition was performed in a seeded crystal growth system. One inhibitory unit (concentration of pentosan polysulfate necessary to give a 50 per cent reduction in the rate of crystal growth) was 5.7 +/- 2 mg./l. at pH 5, 7.2 +/- 1.1 mg./l. at pH 6 and 6.0 +/- 2.1 mg./l. at pH 7. Urine-pentosan polysulfate mixtures showed more inhibitory activity than the predicted inhibition present. Addition of pentosan polysulfate to urine at a concentration of 10 mg./l. increased the inhibitory activity from 45 +/- 3 to 59 +/- 3 IU/l. Pentosan polysulfate is a potent calcium oxalate crystal growth inhibitor in urine at physiologic pH levels. If the urinary concentration of pentosan polysulfate after oral administration reaches 10 mg./l., the increase in inhibitory activity in urine that may occur might be important in the treatment of patients who form calcium oxalate calculi within the urinary tract.