Distribution of flunixin meglumine and firocoxib into aqueous humor of horses.

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used systemically for the treatment of inflammatory ocular disease in horses. However, little information exists regarding the ocular penetration of this class of drugs in the horse.

OBJECTIVE

To determine the distribution of orally administered flunixin meglumine and firocoxib into the aqueous humor of horses.

ANIMALS

Fifteen healthy adult horses with no evidence of ophthalmic disease.

METHODS

Horses were randomly assigned to a control group and 2 treatment groups of equal sizes (n = 5). Horses assigned to the treatment groups received an NSAID (flunixin meglumine, 1.1 mg/kg PO q24h or firocoxib, 0.1 mg/kg PO q24h for 7 days). Horses in the control group received no medications. Concentrations of flunixin meglumine and firocoxib in serum and aqueous humor and prostaglandin (PG) E(2) in aqueous humor were determined on days 1, 3, and 5 and aqueous : serum ratios were calculated.

RESULTS

Firocoxib penetrated the aqueous humor to a significantly greater extent than did flunixin meglumine at days 3 and 5. Aqueous : serum ratios were 3.59 ± 3.32 and 11.99 ± 4.62% for flunixin meglumine and firocoxib, respectively. Ocular PGE(2) concentrations showed no differences at any time point among study groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

Both flunixin meglumine and firocoxib penetrated into the aqueous humor of horses. This study suggests that orally administered firocoxib penetrates the aqueous humor better than orally administered flunixin meglumine at label dosages in the absence of ocular inflammation. Firocoxib should be considered for the treatment of inflammatory ophthalmic lesions in horses at risk for the development of adverse effects associated with nonselective NSAID administration.