Pentosan Injections for Osteoarthritis: Evidence, Safety and Why We No Longer Prescribe Them

What is Pentosan?

Pentosan polysulfate sodium (PPS) is a semi-synthetic polysaccharide derived from plant xylans.

It has been used in medicine for more than 60 years.

The oral form of PPS (brand name Elmiron) is approved in several countries for the treatment of interstitial cystitis, a chronic inflammatory bladder condition.

Researchers later discovered that PPS may have several biological effects relevant to osteoarthritis, including:

• anti-inflammatory activity
• inhibition of cartilage-degrading enzymes
• stimulation of cartilage matrix synthesis
• improvement in blood flow within the subchondral bone
• reduction of bone marrow lesions

Because of these mechanisms, PPS has been investigated as a potential disease-modifying osteoarthritis drug (DMOAD).

Reference
Ghosh P. The role of pentosan polysulfate in osteoarthritis.

Why Pentosan Generated so much Interest in Osteoarthritis

Bone Marrow Lesions in OA

Much of the interest in pentosan relates to its potential effects on bone marrow lesions (BMLs).

Bone marrow lesions are areas of inflammation and micro-damage in the bone beneath the cartilage.

They are commonly seen on MRI scans in patients with osteoarthritis.

Research has shown that:

• bone marrow lesions correlate strongly with pain
• large lesions increase the risk of cartilage loss
• progression of BMLs predicts worsening osteoarthritis

Because pentosan appears to improve blood flow and bone metabolism, it has been proposed that the drug may reduce these lesions.

Reference
Hunter DJ et al. Bone marrow lesions and osteoarthritis progression.

How Pentosan (iPPS) is Administered

When used experimentally for osteoarthritis, PPS is usually given as a subcutaneous injection.

The typical protocol used in early research involved:

two injections per week for six weeks

These injections are administered under the skin, similar to insulin injections.

Importantly:

the medication is not injected into the joint.

This means pentosan acts as a systemic therapy, affecting the entire body rather than a single joint.

This observation has contributed to growing interest in systemic factors in osteoarthritis, including inflammation, metabolic health, and vascular changes within bone.

Evidence for Pentosan in Osteoarthritis

Several early studies have investigated pentosan for osteoarthritis.

These studies suggest the drug may improve:

• knee pain
• joint function
• inflammatory biomarkers
• bone marrow lesions on MRI

Some patients reported meaningful improvements in activity levels and pain reduction.

However, it is important to understand that most of these studies were relatively small or early-phase trials.

Large Phase 3 trials, which are required for regulatory approval, are still ongoing.

Reference
Smith MM et al. Pentosan polysulfate for osteoarthritis: experimental and clinical evidence.

Current Regulatory Status in Australia

Pentosan injections for osteoarthritis are not approved by the Therapeutic Goods Administration (TGA).

Because of this, the medication can only be prescribed through the Special Access Scheme (SAS).

The SAS pathway allows doctors to prescribe medications that:

• are not yet approved in Australia
• have emerging but incomplete evidence
• may help patients when conventional treatments have failed

However, SAS prescribing does not replace the need for formal clinical trials required for full regulatory approval.

Safety Considerations

Like all medications, pentosan has potential side effects.

Known safety considerations include:

• mild anticoagulant effects (increased bruising or bleeding risk)
• gastrointestinal symptoms
• headache
• fatigue

More recently, long-term oral PPS exposure has been associated with a rare condition known as pigmentary maculopathy, affecting the retina.

Although this complication appears related to long-term high-dose oral exposure, the finding has increased regulatory caution.

Reference
Hanif AM et al. Pentosan polysulfate maculopathy.

Because pentosan is currently an off-label therapy, doctors who prescribe it must monitor patients closely for any potential complications.

Why Dr Samra No Longer Prescribes Pentosan

Dr David Samra previously prescribed pentosan through the TGA Special Access Scheme in carefully selected patients.

However, after reviewing the evolving evidence and regulatory landscape, he has chosen not to prescribe pentosan injections at this time.

This decision reflects several considerations:

1. Regulatory status

Pentosan injections remain unapproved for osteoarthritis in Australia.

While SAS prescribing is permitted, it carries additional medico-legal responsibilities.

2. Ongoing clinical trials

Large clinical trials are still underway to determine whether pentosan provides meaningful benefits compared with placebo.

As with all other OA treatments, it is entirely possible that the medication improves symptoms and function, without having any long-term, disease modifying effect.

Until these results are available, the long-term benefits remain uncertain.

3. Safety monitoring

Because pentosan is an off-label systemic therapy, careful monitoring is required.

For patients travelling long distances or seeking treatment from interstate, adequate follow-up can be difficult.

4. Evidence-based practice

At Progressive Sports Medicine we prioritise treatments that are supported by strong clinical evidence and established regulatory approval.

Evidence-Based Osteoarthritis Treatment

While there is ongoing research into new medications, the most effective osteoarthritis treatments remain:

Exercise therapy

Strengthening muscles around the joint improves pain and function.

Weight management

Reducing body weight decreases mechanical load on the joint.

Metabolic health

Systemic inflammation and metabolic factors influence osteoarthritis progression.

Activity modification

Adjusting training loads can help protect joints while maintaining activity.

Injection therapies

In some patients, treatments such as:

• corticosteroid injections
• platelet-rich plasma (PRP)
• hyaluronic acid

may provide temporary symptom relief.

Importantly, these treatments should be considered as part of a comprehensive management strategy, not in isolation.

The Future of Pentosan Research

Research into pentosan continues.

Several ongoing trials (including large-scale, well-designed phase 3 trials) aim to determine whether PPS can:

• improve pain and function
• reduce bone marrow lesions
• slow structural progression of osteoarthritis (this is the hardest to prove but it is what all parties are hoping will be established)

If future studies confirm these benefits with an acceptable safety profile, pentosan may eventually become an approved treatment.

However, until high-quality evidence is available and regulatory approval is granted, it remains an investigational therapy.

Key Takeaways

• Pentosan polysulfate (PPS) is an older drug being investigated for osteoarthritis.
• Early studies suggest potential benefits for pain and bone marrow lesions.
• Large clinical trials are still underway.
• Pentosan injections are not currently approved by the TGA for osteoarthritis.
• Dr David Samra does not currently prescribe pentosan injections.

Patients seeking treatment for osteoarthritis should focus on evidence-based management strategies that improve joint health, strength, and long-term function.

Specialist Osteoarthritis Assessment

If you are experiencing persistent joint pain or osteoarthritis, a detailed assessment can help determine the most appropriate treatment options.

At Progressive Sports Medicine, we provide comprehensive evaluation of:

• joint structure
• biomechanics
• muscle strength
• metabolic health

to develop an individualised management plan.

Medical Disclaimer

This article is intended for educational purposes only and does not constitute medical advice. Individual treatment decisions should always be discussed with a qualified healthcare professional. Progressive Sports Medicine has no commercial relationships with pharmaceutical companies or manufacturers of pentosan products.