Bisphosphonates for Navicular Disease in Horses: When They Help and When To Be Careful

By Dr Duncan Houston

Bisphosphonates can be very useful in selected horses with navicular syndrome, but they are not a shortcut for every horse with heel pain. That distinction matters.

Navicular pain can involve the navicular bone, navicular bursa, deep digital flexor tendon, distal impar ligament, collateral sesamoidean ligaments, coffin joint, hoof balance, or several structures at once. A drug that affects bone turnover may help some horses with bone-associated navicular syndrome, but it will not fix poor shoeing, a deep digital flexor tendon tear, an unbalanced foot, or a missed diagnosis.

This article explains what bisphosphonates do, when drugs such as OSPHOS and TILDREN may be appropriate, what diagnostics should come first, which horses should not receive them, and what owners need to monitor after treatment.

Quick Answer

Bisphosphonates such as clodronate and tiludronate are FDA-approved to control clinical signs associated with navicular syndrome in horses. They are best considered when a horse has a proper diagnosis of navicular syndrome, especially when bone involvement is suspected or confirmed, and should be used alongside corrective farriery and a broader lameness plan. They should not be used casually in young horses, pregnant or lactating mares, breeding animals, horses with renal disease, or without checking competition rules and medication restrictions. (U.S. Food and Drug Administration)

What Is Navicular Syndrome?

Navicular syndrome is a degenerative pain condition involving the structures at the back of the foot, often called the navicular apparatus. It may include the navicular bone, navicular bursa, deep digital flexor tendon, collateral sesamoidean ligaments, distal impar ligament, and related soft tissues. Merck Veterinary Manual describes navicular syndrome as a disease complex rather than one simple bone problem. (Merck Veterinary Manual)

This is why many vets now use terms such as “heel pain” or “podotrochlear pain” rather than treating every case as classic navicular bone disease. The pain may come from bone, soft tissue, synovial structures, or hoof mechanics.

Common signs include:

• Short, choppy front-limb stride

• Intermittent forelimb lameness

• Lameness that shifts between front feet

• Stumbling or toe-first landing

• Reluctance to work on hard ground

• Worsening on circles

• Heel sensitivity to hoof testers

• Improvement after palmar digital nerve blocks

Navicular syndrome is often bilateral, although one front limb may look worse than the other. Many owners think the problem is coming from the shoulder because the horse shortens the front stride, but the pain is often in the foot. (Merck Veterinary Manual)

What Are Bisphosphonates?

Bisphosphonates are drugs that affect bone turnover. In simple terms, bone is constantly being remodelled by cells that build bone and cells that resorb bone. Bisphosphonates reduce bone resorption by affecting osteoclasts, the cells involved in breaking down bone. (U.S. Food and Drug Administration)

In horses, the two FDA-approved bisphosphonates for navicular syndrome are:

The FDA notes that the exact mechanism of action in horses with navicular syndrome is unknown, even though the general drug class is known to reduce bone resorption. That is important because these drugs should not be described as “curing navicular disease.” They help control clinical signs in selected cases. (U.S. Food and Drug Administration)

Bisphosphonates Are Not General Painkillers

This is the first major owner mistake.

Bisphosphonates are not the same as phenylbutazone, firocoxib, or a nerve block. They are not quick painkillers that simply numb the foot.

They are intended for horses with navicular syndrome where bone remodelling is part of the disease process. If the horse’s heel pain is mainly caused by a deep digital flexor tendon tear, poor hoof balance, coffin joint pain, a sole bruise, laminitis, or a collateral ligament injury, bisphosphonates may not address the real problem.

This is why diagnosis matters before treatment. Otherwise, you are using an expensive drug on a vague lameness label and hoping the foot agrees. The foot often does not.

What Does the Research Show for OSPHOS?

The OSPHOS label includes a controlled field study in horses diagnosed with navicular syndrome based on lameness examination, diagnostic nerve blocks, and radiographic signs of bony navicular changes. Horses with radiographic evidence of other conditions such as concurrent soft tissue injury, osteoarthritis, or fractures were excluded from the study. (DailyMed)

At day 56, treatment success was defined as at least a one-grade improvement in the primary affected limb with no worsening in the other forelimb. In that study, the estimated treatment success rate was 74.7% for OSPHOS-treated horses compared with 3.3% for saline-treated controls. At day 180, the estimated overall success rate for OSPHOS was 65.4%. (DailyMed)

That is encouraging, but the study design also tells us something clinically useful: these were horses with a specific navicular diagnosis, not every horse with front-foot soreness. The drug was tested in a defined group.

When Bisphosphonates May Be Appropriate

Bisphosphonates may be worth discussing when:

• The horse is 4 years or older

• A vet has confirmed navicular syndrome

• Diagnostic nerve blocks localise pain to the heel region

• Radiographs show navicular bone changes

• Bone-associated navicular pain is suspected

• Corrective trimming and shoeing have already been addressed

• The horse has chronic or recurrent heel pain

• The horse is not responding adequately to standard management

• Renal function and hydration status are appropriate

• Competition medication rules have been reviewed

Merck lists bisphosphonates as one of several conservative treatment options for navicular syndrome, alongside shoeing changes, rest, NSAIDs, intrasynovial medication, and other therapies. It also notes that shoeing changes are often one of the first conservative management steps. (Merck Veterinary Manual)

The key phrase is one of several options. Bisphosphonates should be part of a plan, not the whole plan.

When Bisphosphonates Are Not the Right First Step

Bisphosphonates are not ideal when:

• The horse does not have a diagnosis

• The lameness has not been localised with nerve blocks

• Hoof balance has not been assessed

• The horse has signs of laminitis

• The horse has an acute hoof abscess or sole bruise

• The horse has a suspected tendon or ligament injury inside the foot

• The horse is younger than 4 years

• The mare is pregnant, lactating, or intended for breeding

• The horse has renal disease or impaired renal function

• The horse is dehydrated

• The horse is receiving NSAIDs without an appropriate washout plan

• The horse is actively competing and medication rules are unclear

The FDA states that the safe use of TILDREN or OSPHOS has not been evaluated in horses under 4 years of age, and that effects on the growing skeleton have not been studied. It also states that safe use has not been evaluated in breeding horses, pregnant mares, or lactating mares. (U.S. Food and Drug Administration)

That is not fine print. That is the part owners need to read before someone says, “Let’s just try it.”

Why Diagnosis Comes First

A proper navicular work-up may include:

• Lameness examination

• Hoof tester assessment

• Watching the horse on straight lines and circles

• Flexion tests where appropriate

• Diagnostic nerve blocks

• Radiographs

• Hoof balance assessment

• MRI if soft tissue injury is suspected

• CT in selected cases

• Review of trimming and shoeing history

Merck notes that diagnosis of navicular syndrome is based on clinical signs and imaging, and that MRI can define lesions across the podotrochlear apparatus, including structures that radiographs cannot fully assess. Horses may have heel pain and soft tissue injury even when radiographic changes are limited. (Merck Veterinary Manual)

This is clinically important. If a horse has a deep digital flexor tendon lesion within the foot, a bisphosphonate may make the owner feel like something advanced has been done, while the real lesion still needs a different plan.

Radiographs vs MRI

Radiographs are useful for assessing bone changes, including navicular bone sclerosis, enlarged vascular channels, flexor cortex changes, distal border fragments, or other bony abnormalities. They are often the first imaging step in suspected navicular syndrome. (Merck Veterinary Manual)

MRI is more useful when the concern is soft tissue injury, such as:

• Deep digital flexor tendon lesions

• Navicular bursa involvement

• Distal impar ligament injury

• Collateral sesamoidean ligament injury

• Coffin joint-related soft tissue pain

• Complex heel pain with unclear radiographs

The practical point is simple: radiographs show bone well, but they do not show every painful structure inside the foot.

OSPHOS vs TILDREN

Both drugs are bisphosphonates approved for navicular syndrome, but they are administered differently.

OSPHOS is given by intramuscular injection, with the total volume divided across multiple injection sites. The label states that clinical improvement is most evident around 2 months after treatment, and horses that initially respond but do not maintain improvement for 6 months may be re-treated at 3 to 6 month intervals based on recurrence of clinical signs. (DailyMed)

TILDREN is administered as an intravenous infusion over 90 minutes. The FDA states that horses should be observed closely after treatment for colic or other adverse reactions, and that maximum clinical effect may take around 2 months. (U.S. Food and Drug Administration)

Neither drug should be treated as an instant fix. Owners should not expect the horse to walk out of the barn the next day looking like it has downloaded new feet.

Safety Warnings Owners Need To Know

Bisphosphonates can cause adverse reactions. The main concerns are gastrointestinal signs, renal toxicity, electrolyte shifts, and the unknown long-term effects of repeated use in some horses.

The FDA states that bisphosphonates can cause gastrointestinal and renal toxicity, are excreted by the kidneys, and are not recommended in horses with impaired renal function. They should be used cautiously with other potentially nephrotoxic drugs, and renal function should be monitored where appropriate. (U.S. Food and Drug Administration)

Important safety points include:

• Do not use in horses with impaired renal function or a history of renal disease.

• Avoid concurrent NSAID use unless your vet has made a specific plan.

• Make sure the horse is well hydrated before and after treatment.

• Monitor water intake and urine output after treatment.

• Watch for colic signs shortly after administration.

• Use caution in horses with electrolyte disorders such as HYPP or hypocalcaemia.

• Do not use in pregnant or lactating mares.

• Do not use in mares intended for breeding.

• Do not use in horses under 4 years of age.

The OSPHOS label specifically warns that NSAIDs should not be used concurrently because of the risk of renal toxicity and acute renal failure. It also advises monitoring water intake and urine output for 3 to 5 days after treatment. (DailyMed)

NSAIDs and Bisphosphonates

This deserves its own section because it is a common trap.

Many horses with navicular pain are already receiving NSAIDs such as phenylbutazone or firocoxib. Bisphosphonates and NSAIDs can both affect the kidneys, so using them together can increase renal risk.

The FDA states that no safe window has been determined for concurrent NSAID use with TILDREN or OSPHOS, and that giving an NSAID from 48 hours before to 48 hours after treatment may be especially risky. The washout period should be decided by the veterinarian based on the horse’s age, condition, and renal status. (U.S. Food and Drug Administration)

Do not simply stop or start NSAIDs yourself. The treating vet needs to balance pain control, kidney safety, hydration, and the specific drug plan.

What Side Effects Can Happen?

Possible adverse effects include:

• Colic signs

• Pawing

• Agitation

• Abdominal discomfort

• Reduced appetite

• Lethargy

• Increased drinking

• Increased urination

• Injection-site swelling or soreness

• Electrolyte changes

• Renal problems

• Abnormal behaviour

• Rare serious adverse events

For OSPHOS, the label states that discomfort, nervousness, cramping, pawing, or colic signs occurred within 2 hours in some treated horses, with most resolving after hand walking. Injection-site reactions were also reported and resolved within 10 days in the target animal safety study. (DailyMed)

For TILDREN, the FDA reports that adverse reactions most commonly occurred during the infusion or within 4 hours afterward, with colic being the most common reaction. (U.S. Food and Drug Administration)

This does not mean every horse will have a reaction. It means treatment should be planned, monitored, and performed by a veterinarian.

How Worried Should You Be?

Low Risk

This is lower concern if the horse:

• Is 4 years or older

• Has confirmed navicular syndrome

• Has normal renal function

• Is well hydrated

• Is not pregnant, lactating, or intended for breeding

• Is not receiving NSAIDs around treatment without a vet-approved plan

• Has had hoof balance and shoeing addressed

• Has no signs of acute colic or systemic illness

What to do: bisphosphonates may be a reasonable option if your vet believes bone-associated navicular syndrome is part of the problem.

Moderate Risk

This is more concerning if the horse:

• Has mild kidney concerns

• Is older or systemically unwell

• Has a history of colic

• Needs NSAIDs for pain control

• Has unclear diagnosis

• Has no recent bloodwork

• Has not had hoof balance assessed

• Is competing under strict medication rules

What to do: ask for a clearer diagnosis, renal assessment, medication plan, and competition rule review before treatment.

High Risk

This is high concern if the horse:

• Has impaired renal function

• Has a history of renal disease

• Is dehydrated

• Is on NSAIDs with no washout plan

• Is under 4 years old

• Is pregnant or lactating

• Is intended for breeding

• Has suspected soft tissue injury rather than bony navicular disease

• Has not had lameness localised with blocks or imaging

What to do: do not use bisphosphonates casually. The horse needs a better diagnostic and risk plan first.

Critical

This is urgent if the horse develops:

• Severe colic signs after treatment

• Depression or collapse

• Not eating

• Marked reduction or increase in urination

• Signs of dehydration

• Severe injection-site swelling

• Severe lameness worsening

• Fever

• Recumbency or abnormal behaviour

What to do: contact your vet urgently.

When Is This an Emergency?

Call your vet urgently if your horse shows:

• Repeated pawing, rolling, or flank watching after treatment

• Persistent or severe colic signs

• Refusal to eat

• Depression or marked lethargy

• Reduced urine output

• Excessive urination or drinking

• Signs of dehydration

• Collapse or recumbency

• Severe injection-site swelling

• Hives or facial swelling

• Fever

• Rapidly worsening lameness

Mild short-lived discomfort may occur after bisphosphonate administration, but severe, persistent, or worsening signs are not something to monitor casually from the fence. The kidneys and gut are the two systems I would be watching closely.

Competition and Racing Considerations

For competition horses, bisphosphonates must be handled carefully. The AAEP states that bisphosphonates in competing horses should be used with discretion, restricted to labelled products used in horses with appropriate signalment and diagnosis, administered according to the manufacturer label, and used in accordance with the rules of the event or governing body. (AAEP)

This matters because drug detection rules vary between organisations and countries. A horse that competes under FEI, USEF, racing, breed association, or local rules may have specific medication restrictions or stand-down requirements.

Before giving a bisphosphonate to a competition horse, ask:

• Is this drug permitted under this horse’s governing body?

• What is the recommended detection or withdrawal guidance?

• Does the horse need to be declared?

• Is the horse eligible to compete after treatment?

• Are there age restrictions?

• Are there racing-specific rules?

• Is there documentation of diagnosis and treatment?

This is not just paperwork. It is welfare, compliance, and protecting the horse and owner from avoidable problems.

What Else Can Look Like Navicular Disease?

Heel pain is not always navicular syndrome.

Important differentials include:

• Deep digital flexor tendon injury

• Coffin joint arthritis

• Collateral ligament injury of the coffin joint

• Navicular bursa inflammation

• Distal impar ligament injury

• Sole bruise

• Hoof abscess

• Laminitis

• Thin soles

• Long toe and low heel imbalance

• Contracted heels

• Poor shoe fit

• Sheared heels

• White line disease

• Pedal osteitis

• Coffin bone fracture

• Suspensory ligament injury

• Shoulder or upper limb lameness that mimics foot pain

This is why “navicular” should not become a rubbish-bin diagnosis for any front-end lameness. The treatment depends on which structure is actually painful.

What Should Be Done Before Using Bisphosphonates?

Before treatment, a sensible checklist includes:

1. Perform a full lameness examination.

2. Localise pain with diagnostic nerve blocks.

3. Take quality hoof radiographs.

4. Assess hoof balance, toe length, heel support, and breakover.

5. Consider MRI if soft tissue injury is suspected.

6. Review current NSAID use.

7. Check hydration and kidney risk.

8. Consider bloodwork in older or higher-risk horses.

9. Confirm the horse is at least 4 years old.

10. Confirm the horse is not pregnant, lactating, or intended for breeding.

11. Review competition or racing rules.

12. Discuss expected response time and recheck plan.

The most important question to ask your vet is:

Are we treating confirmed navicular syndrome with bone involvement, or are we hoping bisphosphonates fix unexplained heel pain?

That question changes the whole plan.

What Happens After Treatment?

After bisphosphonate treatment, owners should monitor:

• Appetite

• Behaviour

• Colic signs

• Water intake

• Urination

• Injection sites, if OSPHOS was used

• Lameness pattern

• Work tolerance

• Response to farriery changes

• Any need for NSAIDs

• Overall comfort over the next several weeks

Clinical improvement may take weeks, with maximum improvement often expected around 2 months. The OSPHOS label notes that improvement is most evident at 2 months post-treatment, and the FDA gives similar timing guidance for both products. (U.S. Food and Drug Administration)

This is important because owners sometimes expect a rapid pain-killing effect. If the horse is not improved the next day, that does not automatically mean treatment failed. If the horse is acutely worse, colicky, or systemically unwell, that is different and needs veterinary attention.

Bisphosphonates Do Not Replace Farriery

Corrective trimming and shoeing remain central to navicular management.

Farriery goals may include:

• Reducing delayed breakover

• Improving heel support

• Correcting long toe and low heel imbalance

• Reducing strain on the deep digital flexor tendon

• Supporting the back of the foot

• Improving landing pattern

• Protecting thin soles

• Matching the trim to radiographic findings

Merck lists trimming and shoeing changes as a key treatment for navicular syndrome and notes that conservative management often begins with shoeing changes such as rolling or rockering the toe or placing the shoe more palmarly to reduce breakover distance. (Merck Veterinary Manual)

In practice, the horse that responds best usually has a whole plan: diagnosis, hoof balance, workload adjustment, pain management, and then medication if appropriate. Giving OSPHOS or TILDREN while leaving a long toe and collapsed heel is like buying premium tyres and ignoring the broken axle.

Common Mistakes Owners Make

Treating Heel Pain Without a Diagnosis

Bisphosphonates should not be used just because a horse has vague front-foot lameness. The pain needs to be localised and the likely structures identified.

Skipping Hoof Balance

Navicular horses often need thoughtful farriery. Medication without hoof correction is usually an incomplete plan.

Using Them in Young Horses

The safe use of OSPHOS and TILDREN has not been evaluated in horses less than 4 years old, and their effect on growing bone is not fully understood. (U.S. Food and Drug Administration)

Ignoring NSAID Risk

NSAIDs should not be used concurrently with OSPHOS or TILDREN unless your vet has made a specific risk-based plan. The concern is renal toxicity and acute renal failure. (U.S. Food and Drug Administration)

Expecting an Instant Result

Maximum improvement may take up to around 2 months. These drugs are not instant nerve blocks.

Using Them in Breeding Animals

The safe use of these drugs has not been evaluated in breeding horses, pregnant mares, or lactating mares, and bisphosphonates can remain in bone for long periods. (U.S. Food and Drug Administration)

Not Checking Competition Rules

Competition medication rules can be strict. Check the relevant governing body before treatment, not after the horse tests positive.

Can Navicular Syndrome Be Prevented?

Not every case can be prevented, but risk may be reduced by managing hoof mechanics and workload carefully.

Practical prevention includes:

• Maintain a consistent farrier schedule.

• Avoid long toes and underrun heels.

• Use radiographs when hoof balance is difficult to judge.

• Address poor landing patterns early.

• Avoid repeated hard work on unforgiving ground.

• Manage body weight.

• Build fitness gradually.

• Investigate recurring front-foot soreness early.

• Do not keep riding through a short, choppy stride.

• Use appropriate shoes, pads, or boots where indicated.

• Recheck horses with known navicular changes before increasing workload.

The best prevention is not one drug. It is good feet, early diagnosis, sensible surfaces, and not pretending a horse that is stabbing the ground toe-first is “just being lazy.”

Will My Horse Return to Work?

Many horses with navicular syndrome can return to useful work, but the prognosis depends on what structures are involved.

The outlook is better when:

• Pain is diagnosed early

• Hoof balance can be improved

• Radiographic changes are mild to moderate

• Soft tissue injury is absent or mild

• The horse responds to farriery

• Bisphosphonates are used in an appropriate case

• Workload is adjusted realistically

The outlook is more guarded when:

• MRI shows significant deep digital flexor tendon damage

• Severe navicular bone degeneration is present

• Both front feet are badly affected

• The horse has chronic long toe and low heel imbalance

• The horse has not responded to multiple treatments

• Competition demands are high

• Pain returns quickly after each treatment

Merck describes navicular syndrome as progressive, with treatment often palliative and sometimes lifelong. The prognosis is guarded to fair, although many horses respond positively to management for a period. (Merck Veterinary Manual)

That is the honest answer. Some horses return well. Some need a lower-level job. Some need ongoing management. Some eventually become pasture-sound rather than performance-sound.

FAQs

Do bisphosphonates cure navicular disease in horses?

No. Bisphosphonates help control clinical signs associated with navicular syndrome in selected horses, but they do not cure every cause of heel pain and do not replace farriery, imaging, workload management, or a full lameness plan. (U.S. Food and Drug Administration)

Is OSPHOS safe for all horses?

No. OSPHOS should not be used in horses with impaired renal function or a history of renal disease, and its safe use has not been evaluated in horses under 4 years old, pregnant or lactating mares, or breeding horses. NSAIDs should not be used concurrently because of renal risk. (DailyMed)

How long does OSPHOS take to work?

Clinical improvement is often most evident around 2 months after treatment. Some horses may show improvement earlier, but owners should not expect an instant response. (DailyMed)

Should my horse have an MRI before bisphosphonates?

Not every horse needs MRI, but MRI is very useful when soft tissue injury is suspected or when radiographs do not explain the lameness. Bisphosphonates are more logical when bone-associated navicular syndrome is part of the diagnosis. (Merck Veterinary Manual)

Can a competition horse receive bisphosphonates?

Possibly, but only with proper diagnosis, labelled use, veterinary oversight, and careful review of the relevant competition rules. The AAEP advises that bisphosphonates in competing horses should be used with discretion and in accordance with manufacturer labels and event regulations. (AAEP)

Final Thoughts

Bisphosphonates have an important place in treating selected horses with navicular syndrome, especially when bone remodelling is part of the pain picture. OSPHOS and TILDREN can improve comfort in some horses and may help them return to work as part of a broader management plan.

But they are not a magic injection for every horse with sore heels.

The safest approach is diagnosis first, treatment second. Localise the lameness, image the foot, assess hoof balance, rule out soft tissue injury where needed, review kidney and medication risks, and check competition rules before treatment.

Used properly, bisphosphonates can be a valuable tool. Used casually, they can distract from the real problem and create unnecessary risk.

The best navicular treatment plan is rarely one thing. It is good diagnostics, good farriery, sensible workload, targeted medication, and honest expectations.

If your horse has navicular syndrome, chronic heel pain, confusing radiographs, or you are unsure whether OSPHOS, TILDREN, MRI, shoeing changes, or another treatment should come next, ASK A VET™ can help you understand what questions to ask your treating vet before making the next decision.