Today's Veterinary Practice

MAR-APR 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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44 ACUTE GLAUCOMA: A TRUE EMERGENCY PEER REVIEWED ACUTE GLAUCOMA: A TRUE EMERGENCY 44 Maintenance Therapy to Control IOP All of the emergency methods to reduce IOP have limited durations of efficacy. Thus, once IOP has been reduced, additional therapy to maintain control of the IOP should be instituted. Carbonic Anhydrase Inhibitors Both systemic and topical carbonic anhydrase inhibitors (CAIs) are available. Inhibition of carbonic anhydrase decreases AH production by reducing synthesis of bicarbonate in the ciliary body. 9–11 ■ Methazolamide is an oral CAI that can be used in dogs for control of IOP. ■ Commonly used dosages include 2.5 to 5 mg/kg PO q8–12h. ■ Methazolamide has potential adverse systemic effects, including gastrointestinal upset, metabolic acidosis, and hypokalemia. ■ I use this medication to treat glaucoma in dogs only if it cannot be treated topically. ■ Topical CAIs have the advantage of providing adequate ocular concentrations of the drug and reducing the risk for systemic adverse effects. ■ Brinzolamide (Azopt; ) and dorzolamide (Trusopt; ) are commercially available and reduce IOP effectively in dogs and cats. Dorzolamide 2% is available in a generic form, which makes it more cost-effective. ■ The degree of IOP reduction observed with topical CAIs is similar to that of oral CAIs, and combination of the drugs does not further decrease IOP. ■ The most common adverse effect of topical dorzolamide is transient blepharospasm after instillation; this is less common with brinzolamide. ■ Topical CAIs are most often used q8–12h. β-Blockers β-Blockers reduce the formation of AH via their effects on β receptors present in the ciliary body. Undesirable cardiac and respiratory effects can be seen with topical β-blockers, including bradycardia and bronchoconstriction. Thus, these medications should be avoided in patients with cardiovascular disease and asthma. 11,12 ■ The degree of IOP reduction with β-blockers is mild; thus, these medications are often combined with other antiglaucoma therapy. ■ A solution of 2% dorzolamide and 0.5% timolol (Cosopt; ) is available in generic form. This combination therapy is as efficacious in reducing IOP as concurrent use of each drug, but the combination improves client compliance because it requires only 1 drop to be instilled 2 to 3 times daily. ■ Betaxolol and timolol are also commonly used as prophylactic treatment for prolonging the onset of glaucoma in the fellow eye of dogs with primary glaucoma. 13,14 ■ β-Blockers are most often used q12h. Miscellaneous Therapy for Acute Glaucoma Pain Control Pain control is advocated for most patients during an acute glaucoma spike. Systemic pain control will improve patient comfort and also likely improve compliance for repeated IOP measurements. Numerous analgesic medications are available; however, I generally use one of the following options: ■ Methadone, 0.2 to 0.3 mg/kg IV q4–6h ■ Tramadol, 4 to 6 mg/kg PO q8–12h Anti-inflammatories Anti-inflammatory therapy is indicated in most cases of acute glaucoma. Topical anti-inflammatories are beneficial for ocular surface inflammation and also treat any anterior segment inflammation. The frequency of use and drug chosen depends on the degree of inflammation, the presence of concurrent uveitis, and the health of the cornea. Most patients are treated q8–12h. Topical nonsteroidal anti- inflammatories should be avoided because they can reduce the efficacy of latanoprost therapy and Topical anti-inflammatories are beneficial for ocular surface inflammation and also treat any anterior segment inflammation.

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