Because of the possibility that regional inflammation of the upper airway may be responsible for some obstructive upper airway diseases, enteral, parenteral, and topical antiinflammatory therapy may prove useful in their treatment. Although a proven correlation between airway inflammation and upper airway obstructive diseases remains to be established, an association exists between the presence of upper airway inflammation and the occurrence of obstructive upper airway disease. This premise finds support in numerous anecdotal accounts of improved upper airway function in horses after antiinflammatory treatment.
Systemic and inhaled corticosteroids have been used successfully to treat upper airway inflammation and neuromuscular dysfunction that results in dorsal and lateral nasopharyngeal collapse and dorsal displacement of the soft palate. After a thorough physical examination and complete blood cell count and fibrinogen have been performed to rule out active bacterial infection, systemic corticosteroid therapy can be initiated. Dexamethasone can be administered in a tapering dose, orally, at 0.02 to 0.04 mg/kg twice daily for 10 days to 2 weeks, followed by 0.02 to 0.04 mg/kg, once daily for 10 days to 2 weeks, then 0.02 to 0.04 mg/kg every other day for 2 weeks. The horse should be rested during this time, and either turned out in a pasture or worked lightly for 6 to 8 weeks. The airway inflammation typically resolves within 7 to 10 days, however, upper airway function may not improve for as long as 4 months, thus patience is important. Oral prednisolone can also be given at 1 to 2 mg/kg with the same dosing regimen as dexamethasone. It is important to note that oral prednisone therapy in horses is ineffective. Prednisone is poorly absorbed by the equine gastrointestinal tract and is not converted to the active antiinflammatory form, prednisolone.
Inhaled and topical medications have also been used to decrease airway inflammation in horses. Dexamethasone and prednisolone can be nebulized for distribution in the nasopharynx. Antiinflammatory topical throat sprays, composed of nitrofurazone, dimethyl sulfoxide, glycerin, and prednisolone or dexamethasone, can be administered into the nasopharynx by passing a uterine infusion pipette or narrowing tubing of sufficient length into the nasopharynx and spraying 10 to 20 ml of the solution into the nasopharynx. Application of throat spray may be performed twice daily for 2 weeks and then daily for 2 weeks.
Interferons are a family of proteins that have antiviral and immunomodulatory activity. Oral administration of a low dose (0.1 IU/kg) of human interferon-α (HuIFNα) reduces tracheal and nasopharyngeal exudate in racehorses with inflammatory airway disease. Horses are generally treated daily for 5 to 7 days. Oral administration of HuIFNα likely is effective because it stimulates lymphoid tissue in the oropharynx. At Michigan State University the following procedure is used to prepare interferon:
1. Add 1 ml of interferon α-2a (3 million U/ml, Roferon-A) to 99 ml of 0.9% saline and mix well but do not shake. This makes 100 ml of 30,000 U/ml interferon α-2a.
2. Remove 143 ml of 0.9% saline from a 1-L container and add 3 ml of the 30,000 U/ml interferon α-2a solution. The final volume of 900 ml will contain 100 U/ml interferon α-2a.
3. Divide the 100 U/ml solution into aliquots of 30 ml each, place in 1 oz bottles, and refrigerate.
4. Label each aliquot with the following information:
- • Interferon α-2a 100 U/ml.
- • Store in refrigerator.
- • Prepared on date _____.
- • Discard after 30 days.
Discard any solution remaining from step 1. Interferon tends to bind to surfaces and any long-term storage must be in a – 70° C freezer.