Antifibrinolytic drugs such as aminocaproic acid (epsilon aminocaproic acid, or EACA) are generally used to treat various bleeding disorders in horses.¹ Aminocaproic acid is often used to help stabilize a clot or slow bleeding in horses with guttural pouch hemorrhage. When bleeding occurs in an organ or body part, a process called hemostasis is set in motion to stop the bleeding. Hemostasis requires an adequate number of platelets, the right amount of blood clotting proteins (referred to as factors), and blood vessels that constrict properly in order to function. 

The most common cause of hemorrhage is usually vascular injury; however, the possibility of hemostatic failure should be considered in any initial diagnosis.² Many different proteins are involved in the clotting process, and deficiencies in any of these can cause bleeding disorders. Such disorders may be congenital (present at birth); they may also develop later in a horse’s life or as the result of disease processes.³

Guttural Pouch Disease in Horses

The guttural pouch is a unique structure found in horses and limited other species. This organ is an extension of the Eustachian tube, an air-filled canal that connects the throat to the middle ear. There is one guttural pouch on each side of the horse’s head, located just below the ear in the throatlatch region. The function of the guttural pouch remains unknown, but possible uses include pressure equalization across the ear drum, warming of inhaled air, a resonating chamber for vocalization, and to aid in the cooling of blood that flows to the brain during exercise.⁴

There are a number of disorders that can arise which affect the guttural pouch and give rise to bleeding that can be from moderate to severe. Among them are:

Gutteral Pouch Empyema

Guttural pouch empyema is defined as an accumulation of purulent, septic exudate in the guttural pouch. This infection usually develops subsequent to a bacterial infection, usually Streptococcus spp.⁵

Guttural Pouch Mycosis 

Guttural pouch mycosis is a fungal infection of one or both guttural pouches and is the most common cause of severe hemorrhage from the guttural pouch. Fungal plaques form within the guttural pouches, most commonly along the walls of the major blood vessels. Over time, the fungus can erode through the wall of vessels, resulting in hemorrhage that can be life threatening. If left untreated, a fatal bleed often occurs. Aspergillus is the most common type of fungus identified in cases of guttural pouch mycosis.³

Guttural Pouch Tympany

Guttural pouch tympany is seen in horses ranging from birth to 1 yr of age and is more common in fillies than in colts. A genetic basis of disease has been identified in Arabian and German warmblood breeds. In some cases, the condition is acquired due to inflammation of the upper respiratory tract. The affected guttural pouch is distended with air and forms a characteristic nonpainful swelling in the parotid region.⁵

Longus Capitis Muscle Rupture

Traumatic rupture of the longus capitis is the second most common cause of severe hemorrhage from the guttural pouch after mycosis. The longus capitis muscle is one of the ventral straight muscles of the head. It inserts on the basisphenoid bone at the base of the skull. The point of rupture occurs at the insertion of the muscle dorsal to the guttural pouch.⁵

Aminocaproic Acid for Horses

Aminocaproic acid is a hemostatic that is used for the treatment of hyperfibrinolysis and as a prophylaxis for postoperative bleeding, primarily in dogs and horses. It inhibits fibrinolysis via its inhibitory effects on plasminogen activator substances and some antiplasmin activity. 

In horses, a plasma concentration of 5.8 µg/mL is sufficient to inhibit fibrinolysis. In a study in which aminocaproic acid 70 mg/kg IV was given to horses over 20 minutes, the drug was distributed rapidly, and plasma levels remained above the proposed therapeutic concentration of 130 µg/mL for 1 hour after the end of the infusion. Elimination half-life was 2.3 hours.⁶

Aminocaproic acid is contraindicated in patients with active intravascular clotting, especially those with disseminated intravascular coagulation (DIC), which can result in fatal thrombus formation. 

As an antifibrinolytic for guttural pouch hemorrhage in horses (extra-label), Plumb’s Veterinary Drugs recommends 40 mg/kg IV bolus of aminocaproic acid, followed by 10 – 20 mg/kg every 6 hours. Data suggest current equine dosing regimens may be higher than necessary after in vitro analysis revealed that the aminocaproic acid plasma concentration needed to inhibit fibrinolysis in horses was 1/20 of the concentration needed in human plasma.⁶

Where to buy Aminocaproic Acid 

Aminocaproic Acid is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. AMINOCAPROIC ACID 250 MG/ML by NexGen Pharmaceuticals is indicated for a variety of bleeding disorders in the horse, including guttural pouch hemorrhage. 

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

¹Fletcher, D.J., et. al. Therapeutic Plasma Concentrations of Epsilon Aminocaproic Acid and Tranexamic Acid in Horses, Journal of Veterinary Medicine, 01 October 2013.

²Brooks, M.B. Equine coagulopathies. Vet Clin North Am Equine Pract. 2008 Aug;24(2):335-55, vi.

³MSD Veterinary Manual.

⁴Smith, K.M., Barber, S.M. Guttural pouch hemorrhage associated with lesions of the maxillary artery in two horses. The Canadian veterinary journal = La revue veterinaire canadienne vol. 25,6 (1984): 239-42.

⁵Merck Veterinary Manual.

⁶Plumb’s Veterinary Drugs.