Pentoxifylline is a hemorrheologic and immunomodulatory agent that is used in horses for the treatment of navicular disease, and as an adjunctive therapy for cutaneous vasculitis, placentitis, atopic dermatitis and endotoxemia. It increases erythrocyte flexibility and reduces inflammation, and is rapidly absorbed with a wide variation of bioavailability that averages around 68%¹

Navicular disease (or Navicular syndrome) is a group of related conditions affecting the navicular bone and associated structures in the foot of the horse. It is characterized by inflammation or degeneration of the navicular bone and its surrounding tissues, usually in the front feet of the horse. The syndrome can lead to significant or disabling lameness of a horse. The navicular bone is located between the pedal bone and the deep digital flexor tendon.²

The primary cause of navicular disease is not known, although it is thought that damage to the navicular bone may occur due to interference with blood supply or trauma to the bone. This damage can occur to the deep flexor tendon, navicular bursa, or navicular ligaments, resulting in pain and lameness.³ Navicular disease causes a low grade bilateral lameness, which can occur intermittently when the horse is exercised. In some cases, one foot is affected more than the other, causing noticeable lameness. Affected horses may stand with the more painful foot in front placed of the other. A diagnosis of navicular disease is based on a combination of history, symptoms, nerve blocks and radiography. A history of intermittent or recurrent lameness is often indicative of navicular disease.²

Cutaneous vasculitis (inflammation of blood vessels) in caused by immune complexes occurring in the horse. This causes the skin to develop reddened areas that quickly erode into scabbed sores. Depending on which blood vessels are involved, the sores may appear on the legs, mouth, or lips. The limbs may also swell due to fluid accumulation under the skin. Vasculitis is usually diagnosed via tests on skin samples from the affected areas.⁴

Atopic dermatitis is an allergic reaction to environmental allergens such as pollens, barn dust and molds. It can occur seasonally or be present throughout the year. The three most common symptoms are urticaria (or hives), itching or pruritus alone. The latter commonly affects the face and trunk. Diagnosis of atopic dermatitis is based on clinical signs and the exclusion of other diagnoses. In some cases, a horse can have a secondary bacterial skin infection that gives rise to or exacerbates the condition.⁵

Endotoxemia is a serious inflammatory response to gram-negative bacteria that can lead to vital organ and circulatory system failure in horses. It often occurs after a horse has struggled with an illness such as colic, pneumonia or a severe infection. Endotoxemia can cause a horse’s vital organs to fail and its circulatory system to collapse. Symptoms of endotoxemia in horses can include lethargy, fever, dehydration, dark mucous membranes, sweating, increased heart and respiratory rate, compromised intestinal motility and pain.

The endotoxins that give rise to this condition are usually present in environments where horses reside. Horse manure typically harbors high amounts of gram-negative bacteria, making it easy for stabled horses to breathe in a significant amount of endotoxins.⁶

Pentoxifylline for Horses

The mechanisms for pentoxifylline’s actions to improve microcirculatory blood flow are not fully understood. The drug increases flexibility of newly formed erythrocytes probably by inhibiting erythrocyte phosphodiesterase and altering erythrocyte electrolyte concentrations. It decreases blood viscosity possibly by stimulating prostacyclin synthesis and release, reducing plasma fibrinogen, decreasing collagen synthesis, and increasing fibrinolytic activity. The results of one study suggested a potential use for pentoxifylline in treating horses with recurrent airway obstruction, as it effectively reduced reactive oxygen and nitrogen species in pulmonary tissues of affected horses.¹

In horses, IV administration may be associated with transient leukocytosis, muscle fasciculations, sweating on shoulders and flanks, and mild increases in heart rate. Oral dosing at 10 mg/kg or less appears to be well tolerated.

When pentoxifylline is used with warfarin or other anticoagulants, increased risk for bleeding may result. Thus its use with these agents should be done with enhanced monitoring and caution.

NOTE: The Association of Racing Commissioners International Uniform Classification Guidelines for Foreign Substances has designated pentoxifylline as a CLASS 4 DRUG.

Where to buy Pentoxifylline

Pentoxifylline is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. PENTOXIFYLLINE 300 MG/ML PASTE by NexGen Pharmaceuticals is indicated for the treatment of navicular disease, and as an adjunctive therapy for cutaneous vasculitis, placentitis, atopic dermatitis and endotoxemia in the horse.

Pentoxifylline carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Plumb’s Veterinary Drugs.

²vcahospitals.com.

³Belknap, J. K. Navicular Disease in Horses - Musculoskeletal System. Merck Veterinary Manual

⁴Merck Veterinary Manual.

⁵thehorse.com.

⁶wagwalking.com.