Pentosan Polysulfate

Mechanism of action

Pentosan polysulfate sodium (PPS) is a semi-synthetic drug manufactured from beech-wood hemicellulose by sulfate esterification of the xylopyranose hydroxyl groups (Kumagai et al., BMC Clin Pharmacol 2010). The FDA label for oral Elmiron describes it as a semi-synthetically produced heparin-like macromolecular carbohydrate derivative with a molecular weight of 4000 to 6000 Dalton, and as a low molecular weight heparin-like compound with anticoagulant and fibrinolytic effects. It is a polysaccharide, not a peptide. Joint research. In vitro, calcium PPS directly inhibited the aggrecanase activity of ADAMTS4 in interleukin-1alpha-stimulated osteoarthritic chondrocytes; the authors note that aggrecanases are considered to play key roles in aggrecan degradation in osteoarthritic cartilage and suggest that calcium PPS could function as a chondroprotective agent (Takizawa et al., FEBS Lett 2008, PMID 18671975). That is cell-culture evidence. The human knee osteoarthritis studies summarised below are small and report symptoms, function or biomarkers, so whether this enzyme-inhibition mechanism accounts for any clinical effect has not been established here. Bladder. The FDA label states that the mechanism by which PPS achieves its effects in patients is unknown; in preliminary clinical models it adhered to the bladder wall mucosal membrane, and the label says it may act as a buffer that controls cell permeability and keeps irritating solutes in the urine from reaching the cells. A controlled trial (Parsons et al., J Urol 1993) concluded that its results support the concept that some patients with the interstitial cystitis syndrome may have abnormal bladder surface glycosaminoglycans. Both statements are hypotheses rather than an established mechanism. Anticoagulant activity. The FDA label calls Elmiron a weak anticoagulant (1/15 the activity of heparin). At a daily dose of 300 mg (n=128), rectal haemorrhage was reported as an adverse event in 6.3% of patients, and bleeding complications of ecchymosis, epistaxis and gum haemorrhage have been reported. The label advises evaluating patients with signs or symptoms of an underlying coagulopathy or other increased bleeding risk, and caution in patients with a history of heparin-induced thrombocytopenia. Pigmentary maculopathy. Pearce and colleagues (Ophthalmology 2018) described six adults with interstitial cystitis, all treated with PPS, who had a novel pigmentary maculopathy; median cumulative exposure was 2263 g (range 1314-2774 g) over a median of 186 months. They reported that multimodal imaging and functional studies were suggestive of a primary retinal pigment epithelium injury and that additional investigation was warranted to explore causality. The FDA label states that the aetiology is unclear and that cumulative dose appears to be a risk factor.

Pearce and colleagues (Ophthalmology 2018) described six adults with interstitial cystitis and long-term PPS exposure (median cumulative 2263 g) who had a novel pigmentary maculopathy. Later UCLA screening studies found it in 16% to 20% of PPS users who were screened, the FDA label now carries a warning, and the MHRA has advised regular ophthalmic examinations. A 2026 case series (Fung et al., JAMA Ophthalmol) reported the maculopathy after subcutaneous PPS alone in three patients at cumulative doses of 45.5 to 96 g.

— Notable finding

Research history

PPS has been used in both human and veterinary medicine. A 2003 review of suspected adverse reactions to Cartrophen Vet (100 mg sodium pentosan polysulphate per ml) reported to the UK Veterinary Medicines Directorate in dogs between January 1991 and October 1999 covered 161 reports (Hannon et al., J Small Anim Pract 2003, PMID 12779171), so the product was in veterinary use in the UK during that period. Human knee osteoarthritis work with injectable PPS is more recent and mostly small. A randomised, double-blind, placebo-controlled pilot study enrolled 114 patients who received sodium PPS 3 mg/kg or Ringer's solution intramuscularly once a week for 4 weeks (Ghosh et al., Curr Ther Res Clin Exp 2005). A single-centre, open-label trial gave 20 patients 6 weekly subcutaneous injections of 2 mg/kg (Kumagai et al., BMC Clin Pharmacol 2010). A 2026 exploratory phase 2 randomised trial of subcutaneous PPS in 61 participants, whose authors include employees of the sponsor Paradigm Biopharmaceuticals, reported effects on synovial fluid biomarkers (Skerrett et al., Arthritis Res Ther 2026). A larger phase 2/3 trial of subcutaneous PPS in knee osteoarthritis pain (NCT04809376, 602 participants) is listed on ClinicalTrials.gov as active, not recruiting (record last updated 8 April 2024); we did not find a peer-reviewed publication of its results when searching PubMed on 15 October 2026. In the United States, Drugs@FDA lists the original approval of Elmiron (NDA 020193) on 26 September 1996; the label indication is the relief of bladder pain or discomfort associated with interstitial cystitis. The retinal signal emerged later. Pearce and colleagues published a six-patient case series of a novel pigmentary maculopathy in Ophthalmology in 2018. The MHRA published a Drug Safety Update on the risk in September 2019 after a letter to healthcare professionals in July 2019, and the FDA label revised in June 2020 carries a Warnings entry for retinal pigmentary changes. In December 2021 the MHRA added a note that the Summary of Product Characteristics recommends an ophthalmologic examination after 6 months of use and, if there are no pathologic findings, regularly after 5 years of use or earlier in case of visual complaints.

Summarised studies

Safety profile

Pentosan polysulfate has a regulatory safety database from its oral interstitial cystitis use, and the main long-term concern in it is retinal. Common adverse reactions. In the unblinded clinical trial of 2499 interstitial cystitis patients described in the FDA label, adverse events at 1 to 4% frequency included alopecia (4%), diarrhoea (4%), nausea (4%), headache (3%), rash (3%), dyspepsia (2%), abdominal pain (2%), liver function abnormalities (1%) and dizziness (1%). The label says alopecia began within the first 4 weeks of treatment and that 97% of alopecia cases were alopecia areata limited to a single area of the scalp. In a 380-patient, 32-week study of 300, 600 and 900 mg daily doses, most adverse events were mild and resolved without intervention (Nickel et al., Urology 2005). The FDA label reports that at 900 mg daily, a dose higher than the approved dose, rectal haemorrhage was reported in 15% of patients in the 380-patient study, and that in a separate 16-week phase 2 study in 100 men (51 PPS, 49 placebo) elevated liver function tests were reported as an adverse event in 11.8% (n=6) of PPS-treated patients versus 2% (n=1) on placebo. Injectable routes. The FDA label for oral Elmiron states: "A similar product that was given subcutaneously, sublingually, or intramuscularly (and not initially metabolized by the liver) is associated with delayed immunoallergic thrombocytopenia with symptoms of thrombosis and hemorrhage." The label does not name that product. Injectable use in knee osteoarthritis. In the 114-patient intramuscular pilot study, mild bruising at the injection site occurred in fewer than 1% of patients in both groups (Ghosh 2005). In the 20-patient open-label subcutaneous study, the dose used affected the blood coagulation tests but was reported to be within safe levels, and slightly abnormal serum triglycerides were noted (Kumagai 2010). The 61-participant phase 2 trial reported that subcutaneous PPS was well tolerated with no serious related adverse events or adverse events of special interest (Skerrett 2026). Pigmentary maculopathy. In a single-centre prospective screening study from UCLA, prevalence among PPS users who agreed to participate was 16% of 100 patients, with mean cumulative dosage of 3,103 g in the affected group versus 768 g in the unaffected group (Wang et al., Am J Ophthalmol 2021). An earlier cross-sectional study from the same centre found 20% (10/50), and its authors recommended annual retinal imaging, especially as cumulative dosage approaches 500 g, and judged that patients exposed to more than 1500 g are at significant risk (Wang et al., Can J Ophthalmol 2020). Both are single-centre cohorts: the 2021 participants agreed to be screened (self-selected), whereas the 2020 patients were randomly ascertained, and neither should be read as a population-wide risk estimate. The 500 g and 1500 g figures come from studies of PPS users that reported daily doses in mg (the Wang 2021 cohort averaged about 290 to 430 mg per day), i.e. oral use; the Fung paper notes that retinal toxicity had primarily been reported following oral administration, so those figures should not be applied to subcutaneous use. A 2026 case series reported pentosan polysulfate maculopathy in three patients after subcutaneous PPS alone for arthritis, at cumulative doses of 45.5 to 96 g over 7 to 10 years; the authors suggest toxicity can occur with subcutaneous administration alone at much lower doses than with oral use, and advise caution when using subcutaneous PPS (Fung et al., JAMA Ophthalmol 2026, PMID 41379439). The FDA label states that most reported cases occurred after 3 years of use or longer but that cases have been seen with a shorter duration, and that cumulative dose appears to be a risk factor. Course after stopping. The FDA label states that retinal and vision changes may progress even after cessation of treatment. In an 11-patient retrospective case series, no eyes showed a demonstrable improvement after discontinuing PPS, 9 of 11 patients (82%) reported worsening visual symptoms at the final visit, and the authors suggest that the maculopathy continues to evolve after cessation for at least 10 years (Shah et al., JAMA Ophthalmol 2020). Monitoring. The FDA label suggests a baseline retinal examination (including OCT and auto-fluorescence imaging) for all patients within six months of starting treatment and periodically during treatment, and says that if pigmentary changes develop, the risks and benefits of continuing treatment should be re-evaluated because these changes may be irreversible. Symptoms listed in the label are difficulty reading, slow adjustment to low or reduced light environments, and blurred vision.

UK regulatory status

Human use. The MHRA's Drug Safety Update of 19 September 2019 describes pentosan polysulfate as indicated for the treatment of bladder pain syndrome (interstitial cystitis) characterised by either glomerulations or Hunner's lesions in adults with moderate to severe pain, urgency and frequency of micturition, at a recommended 300 mg per day (one 100 mg capsule three times daily), and states that the product information was updated to include the risk of pigmentary maculopathy. The MHRA advised regular ophthalmic examinations for patients taking pentosan polysulfate and asked that suspected adverse reactions be reported to the Yellow Card scheme. The Drug Safety Update's December 2021 note adds that the Summary of Product Characteristics now recommends an ophthalmologic examination after 6 months of use and, if there are no pathologic findings, regularly after 5 years of use. This page does not confirm whether a UK-licensed product is currently on the market: the MHRA product database could not be queried programmatically and the emc search returned no pentosan results on 15 October 2026. Check the MHRA products database before relying on current availability. Knee osteoarthritis. The indication described by the MHRA and by the FDA label is interstitial cystitis bladder pain. The injectable PPS used in the knee osteoarthritis trials discussed on this page was studied as an investigational treatment; we did not find a regulatory approval for it in that indication. Veterinary use. Cartrophen Vet (100 mg sodium pentosan polysulphate per ml) was the subject of adverse-reaction reports to the UK Veterinary Medicines Directorate in dogs between 1991 and 1999 (Hannon et al., 2003). We did not check its current veterinary authorisation, and a veterinary product is not a human medicine. This site does not sell pentosan polysulfate. Nothing here is medical advice; anyone taking it, or considering it, should speak to a prescriber and an eye-care professional.

Frequently asked questions