Currently used in veterinary practice.
Xalatan eye drops (Latanoprost 0.05%)
Latanoprost is a synthetic prostaglandin that reduces IOP by increasing aqueous outflow and causing marked miosis. We use this drug to treat acute glaucoma when the IOP has suddenly increased. Therapy is usually SID. Onset of action is approximately 90 mins however IOP may fall before this time. In many cases vision returns immediately as the IOP decreases. In some cases vision may return over a few days, however after 7 days if the eye remains blind this is likely due to irreversible damage to the optic nerve. This drug is rarely effective long term, however in some patients this is effective for prolonged periods, however if IOP increases BID therapy can be used.
These prostaglandins are not effective in cats. Other synthetic prostaglandins include Travatan (Travoprost 0.004%), Lumigan (Bimatoprost 0.03%) and Alphagan. We sometimes rotate e.g. Xalatan and Travatan drops when the patient appears to become resistant to one or the other.
Trusopt eye drops (Dorzolamide 2%)
Dorzolamide is a topical carbonic anhydrase inhibitor, so these drugs work to reduce intraocular pressure by reducing aqueous production. They are particularly effective for glaucoma secondary to uveitis when IOPs may be increased to the mid 30s mmHg. When used alone to treat acute, primary glaucoma Trusopt is rarely effective, but is useful as an adjunct to topical synthetic prostaglandins.
Duration of action is approximately 8 hours so TID therapy is usually required initially. Many cases may be maintained on BID therapy once IOP has reduced, however close monitoring should take place. In cases of secondary glaucoma, the treatment may be transient for weeks to months then slowly tapered off whilst IOP is monitored.
Trusopt is also used as a prophylactic drug twice daily in eyes predisposed to glaucoma. We may choose this drug for prophylaxis if the fellow eye is already being treated with this drug.
Other topical carbonic anhydrase inhibitors include Cosopt (Dorzolamide 2% and Timolol 0.5%) and Azopt (Brinzolamide). Cosopt is useful for cases whereby the IOP gradually increases on Trusopt. Azopt is useful for cases that develop blepharitis on Trusopt or Cosopt (less than 5% of cases). Azopt is used twice daily.