therapeutic topics
Choosing Allergy Medications
BY WILLIAM TOWNSEND, OD

By the time you receive this issue, spring will have introduced a whole new group of patients to your practice who suffer from seasonal allergic conjunctivitis (SAC). Their complaints vary from mild to severe, intermittent to constant and may include any or all of SAC's classic symptoms: itching, watering, swelling and foreign body sensation. Like most conditions we treat, it's best to take a common sense approach to managing SAC.

Understanding the Process

Allergic conjunctivitis may be either seasonal or perennial. It's a Type I (immediate) hypersensitivity reaction, as most of you know. It's important to review this because the nature of the Type I reaction dictates how you should manage it.

In immediate hypersensitivity, an individual encounters a specific allergen and becomes sensitized to it. Later, when sensitized IgE antibodies on the surface of a mast cell encounter the allergen, the mast cell degranulates and releases pre-formed mediators (histamine, bradykinin, tryptase, heparin and cytokines) into the surrounding tissue. Secondarily, arachidonic acid is converted to newly formed mediators.

Many of the numerous mast cells in a patient's conjunctiva will have degranulated by the time he arrives at your office. The immediate result is that his eyes itch (H₁ effect) and his conjunctiva is swollen (H₂ effect).

Managing the Symptoms

Your immediate concern is to give the patient short-term relief. Your long-term goal is to prevent further misery. You may initially consider a topical steroid, but steroids do nothing for histamine already in the tissue.

A better approach is to introduce a strong antihistaminic agent that acts on both H₁ and H₂ receptors. Blocking both will reduce itching, injection and swelling.

Your second goal is more long term. You know that the patient is sensitized to whatever is in the air. Eventually, this particular allergen will go away, but others may follow. Patient histories will reveal that some individuals seem allergic to a small group of allergens, while others are sensitive to everything.

The best way to prevent subsequent symptoms is by blocking the release of inflammatory mediators from mast cells. The ideal drugs for managing allergic conjunctivitis would block both H₁ and H₂ receptors and would also effectively prevent mast cell degranulation. It's also preferable when both drug types are available in a single medication because of reduced preservative toxicity.

Combination Drugs Do the Trick

Fortunately, several medications meet our requirements. Olopatadine (Patanol, Alcon) combines a mast cell stabilizer with an H₁ histaminic receptor inhibitor. It has a proven record for managing allergic eye disease. Ketotifen fumarate (Zaditor, CIBA Vision) also combines an antihistamine with a mast cell stabilizer. It also acts against H₁ receptor sites.

Recently, Inspire Pharmaceuticals introduced epinastine hydrochloride (Elestat) to the market. It both inhibits histamine release from mast cells and is selective for the H₁ receptor. This drop also reportedly has affinity for the H₂ receptor, in which case it would help reduce edema associated with allergic conjunctivitis. Our patients like its rapid onset of action.

The Bottom Line

Rather than using a pure antihistamine or pure mast cell stabilizer, or using one of each together, use a single product that meets all criteria. Also, nonpreserved artificial tears can help dilute the allergen in the tear film. Finally, Dr. Mom was right to prescribe cold compresses, which can help relieve itchy eyes.

Dr. Townsend is in private practice in Canyon, Texas, and is an adjunct professor at UHCO. E-mail him at drbill1@cox.net.