Itching to Find a New Allergy Treatment?
BY WILLIAM TOWNSEND, OD
Every spring and fall, we see patients with symptoms of stuffy, runny noses and itchy, red, irritated eyes. Allergic rhinitis and its ocular counterpart, allergic conjunctivitis, affects up to 20 percent of the population. A few years ago, we had few options for treating the ocular component of seasonal allergy. In recent years, new, effective and safe medications have been introduced. Generally speaking, they fall into three categories: mast-cell stabilizers, antihistamines and cyclooxygenase inhibitors.
In allergic conjunctivitis, pol-len granules contact mast cells on the ocular surface. The pollen bridges the space between two IgE antibodies on the mast cell surface, which initiates a complex series of events that ultimately leads to the rupture of the mast cell wall and the release of pre-formed mediators such as histamine, eosinophil chemotactic factor of anaphylaxis (ECF-A) and heparin. Histamine binds to receptors that increase vascular permeability leading to tissue edema and itching in nerve endings, while ECF-A leads to recruitment of eosinophils.
The initial symptoms related to pre-formed mediators occur within minutes, while the late phase reaction associate with new synthesized mediators occurs six to 12 hours later.
Traditional approaches to treating allergic conjunctivitis include vasoconstrictors and cold compresses to prevent exudation into the intracellular spaces, antihistamines to block histamine binding sites and mast-cell stabilizers to prevent the release of the above named mediators. The late phase is controlled (somewhat) by topical NSAIDs. Before the introduction of Patanol, it took several different medications to accomplish the goal. Each medication had preservatives, which further irritated the patient's eye.
A New Allergy Weapon
Ketotifen fumarate 0.25% (CIBA Ophthalmics' Zaditor) is a combination mast-cell stabilizer/antihistamine solution. It is also reported to inhibit eosinophil chemotaxis. It is available in 5ml bottles, and its recommended dosage is every eight to 12 hours. Ketotifen is a potent H1 receptor antagonist; for example, it binds to histamine receptors and blocks the action of histamine on these sites. The immediate effect is reduced itching, redness and fluid accumulation with conjunctival tissue.
The second mechanism of action is inhibiting mast cell degranulation. Mast cell degranulation is the initiating event in the chain that causes ocular allergy. By preventing the sequence from occurring, Zaditor blocks the effects of pre formed mediators and newly synthesized mediators. It also prevents the attraction of eosinophils to the site.
Although the role of eosino-phils in allergy is not completely understood, it is believed that by releasing a number of polypeptides and other mediators, they amplify and prolong the allergic reaction. Preventing eosinophil accumulation in tissue therefore greatly reduces the severity of the allergic response.
Our experience with Zaditor has been somewhat limited, since it was released at the end of the allergy season. The patients we've treated with Zaditor have found it to be very effective with a b.i.d. dosing. They reported significant reductions in itching, watering and mucous production, and also reported an overall improvement in ocular comfort.
Although it has not been approved for vernal conjunctivitis, we have found that it in the limited number of cases where we used it for treating this condition, Zaditor was comparable to olopatidine (Alcon's Patanol) in providing relief.
Dr. Townsend is in private practice in Canyon, Texas, and is a consultant at the Amarillo VA Medical Center. E-mail him at firstname.lastname@example.org.