Uveitis is a common and clinically important ophthalmic disorder in domestic cats, and the cause often is not determined. Complications of uveitis include secondary glaucoma,1 synechia, lens luxation,2 cataract formation,1 phthisis bulbi, and blindness. Topical and systemic administration of anti-inflammatory medications is commonly used in the treatment of uveitis in veterinary medicine. Anti-inflammatory drugs are used in conjunction with an antimicrobial agent when an infectious organism is identified. The route of administration of the anti-inflammatory medication is determined on the basis of the severity of inflammation and the location of inflammation within the eye. The goals of anti-inflammatory treatment are to decrease inflammatory mediators, reduce discomfort, and prevent complications associated with intraocular inflammation. In general, topical anti-inflammatory medications are indicated for treatment of inflammation in the anterior segment of the eye. Topical administration of anti-inflammatory medications does not result in therapeutic concentrations in the posterior segment of the eye. Systemic anti-inflammatory medications are generally recommended for the treatment of inflammation in the posterior segment of the eye or as an adjunctive treatment for anterior uveitis.
Anti-inflammatory treatment includes the use of corticosteroids and NSAIDs. Corticosteroids bind to specific receptors in the cytoplasm of cells in the iris, choroid, sclera, cornea, conjunctiva, and retina3,4 and inhibit phospholipase A2 activity on phospholipids, which in turn prevents the biosynthesis of arachidonic acid and subsequent formation of prostacyclin, thromboxane A, PGs, and leukotrienes.5,6 Glucocorticoids can also decrease PG synthesis at the level of the COX pathway,7 and they may induce local expression of somatostatin, a hormone with anti-inflammatory properties.8
Cats appear to be more resistant to the adverse effects of systemically administered glucocorticoids, compared with results in dogs, and reportedly have up to 50% fewer corticosteroid receptors than do dogs.9 In dogs, there is rapid hepatic conversion of prednisone to the active metabolite, prednisolone, which allows both prednisone and prednisolone to be used interchangeably at equivalent dosages. However, in cats, the pharmacokinetics of prednisone are inferior to those of prednisolone,10 and prednisolone is generally recommended over prednisone in cats.
Nonsteroidal anti-inflammatory drugs inhibit PG synthesis by competing with arachidonate for binding to the COX-active site of PG endoperoxide synthase. Prostaglandin endoperoxide synthase, also known as COX, is the enzyme that converts arachidonic acid to PGs (PGE2, PGD2, PGF2α, and PGI2) and thromboxane A2.11 Two main isoforms of COX (COX-1 and COX-2) have been identified; in general, COX-1 is responsible for production of PGs that are required for tissue homeostasis, such as gastric cytoprotection, regulation of renal blood flow, and platelet function.12 In contrast, COX-2 is responsible for production of PGs primarily at sites of inflammation by cells that have been stimulated by cytokines and other inflammatory mediators, although COX-2 can be found in low amounts in physiologically normal tissues.12
The toxic effects of NSAIDs are thought to result primarily from inhibition of COX-1. Cyclooxygenase selectivity is typically expressed as a ratio of the concentrations at which a specific drug inhibits each isoenzyme by 50%. Nonsteroidal anti-inflammatory drugs have been classified on the basis of their selectivity for COX-1 and COX-2 on the assumption that greater selectivity for COX-2 would result in fewer adverse effects but still provide anti-inflammatory and analgesic effects. In general, acetylsalicylic acid is considered to be a nonselective COX inhibitor, indicating that it inhibits both COX-1 and COX-2, whereas meloxicam is classified as a selective COX-2 inhibitor. Cats have a reduced ability for glucuronide conjugation that results in prolonged action of many drugs, including most NSAIDs. Therefore, cats may have an increased risk of complications associated with the use of systemically administered NSAIDs, particularly given that little is known about COX selectivity of various NSAIDs in cats.
Although several ophthalmic studies13–18,a,b have been conducted to evaluate the efficacy of orally administered anti-inflammatory agents in dogs, the authors are not aware of any such reports for cats. Because of species differences in stability of the BAB and differences in the metabolism of drugs, it is clinically relevant to evaluate the efficacy of anti-inflammatory medications in each species. The purpose of the study reported here was to assess the inhibitory effects of 4 orally administered anti-inflammatory medications on paracentesis-induced intraocular inflammation in clinically normal cats via fluorophotometry.
Laus JL, Ribeiro AP, Escobar A, et al. Effects of carprofen administered by different routes to control experimental uveitis in dogs (abstr), in Proceedings. 38th Annu Meet Am Coll Vet Ophthalmol 2007;26.
Payen G, Pepin-Richard C, Bonnaire Y, et al. Evaluation of aqueous concentration and ocular effects of firocoxib following aqueocentesis-induced anterior uveitis in dogs (abstr), in Proceedings. 42nd Annu Meet Am Coll Vet Ophthalmol 2011;57.
SL-14 Biomicroscope, Kowa Co Ltd, Tokyo, Japan.
BioGlo, HUB Pharmaceuticals LLC, Rancho Cucamonga, Calif.
TonoVet, Tiolat Ltd, Helsinki, Finland.
HEINE Omega 180 ophthalmoscope, HEINE Optotechnik, Herrsching, Germany.
Aspirin, Perrigo, Allergan, Mich.
Metacam, Boehringer Ingelheim Vetmedica Inc, St Joseph, Mo.
Qualitest, Huntsville, Ala.
Lloyd Inc, Shenandoah, Iowa.
Domitor, Orion Corp, Espoo, Finland.
VetaKet, IVX Animal Health Inc, St Joseph, Mo.
FM-2 Fluorotron Master, OcuMetrics Inc, Mountain View, Calif.
AK-Fluor 10%, Akorn Inc, Lake Forest, Ill.
Proc GLIMMIX, SAS, version 9.2, SAS Institute Inc, Cary, NC.
McKinnon NJ, Wiechert S, Wang C, et al. Evaluation of intravenous meloxicam in controlling experimental intraocular inflammation (abstr), in Proceedings. 42nd Annu Meet Am Coll Vet Ophthalmol 2011;46.
Dammgen J. The use of metacam 0.5 mg/mL oral suspension in cats with osteoarthritis (abstr), in Proceedings. Metacam Symp Arthritic Dis Cats 2007;19–20.
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