Molecular size affects urine excretion of pentosan polysulfate.

Purpose: In human subjects only a small percent of oral PPS is found in urine. Commercially available PPS is a heterogeneous mixture with varying molecular weights. Our hypothesis was that only the low molecular weight fraction reaches the urine.

Materials And Methods: Urine was obtained from patients with IC who were chronically receiving PPS. The amount and molecular size of PPS in the urine were determined by enzyme-linked immunosorbent assay and molecular sieve chromatography. PPS was purified from Elmiron capsules and fractionated into LMW and HMW fractions. Urine recovery of PPS was measured in rabbits after oral or intravenous administration of unfractionated, LMW or HMW PPS.

Results: The median urine PPS level in 34 patients with IC was 1.2 microg/ml (range 0.5 to 27.7). All PPS recovered from IC urine was LMW. After intravenous administration in rabbits the median recovery in urine was 47.2% (range 19.7% to 73.2%) for unfractionated PPS, 74.6% (range 31.4% to 96.3%) for LMW and 3.3% (range 2.5% to 5.0%) for HMW. After oral administration in rabbits the median recovery in urine was 7.4% (range 2.1% to 46.0%) for LMW and 0.10% (range 0.0% to 0.3%) for HMW.

Conclusions: In patients with IC who are on oral PPS the PPS recovered in the urine is all of LMW. In rabbits the HMW fraction of PPS is recovered in small amounts from urine after intravenous administration and not at all after oral administration.