New ophthalmic formulations of ketotifen fumarate, pemirolast potassium and nedocromil sodium have recently received labeling approval from the U.S. Food and Drug Administration for the treatment of adults and children with itchy eyes resulting from allergic conjunctivitis. Pemirolast and nedocromil are mast-cell stabilizers; ketotifen, in addition to this property, also has H₁-receptor antagonist activity. Inhaled nedocromil has been available in the United States since 1993. Consultants from the Medical Letter reviewed the effectiveness and safety of new ophthalmic formulations for the treatment of patients with allergic conjunctivitis.

Over-the-counter antihistamine-decongestant combinations for ophthalmic use have a short duration of effectiveness and can cause rebound vasodilation with sustained use. Ophthalmic mast-cell stabilizers (i.e., cromolyn and lodoxamide) and H₁-receptor antagonists (i.e., levocabastine and emedastine) have been shown to be effective in the treatment of patients with seasonal allergic conjunctivitis. Like ketotifen, olopatadine is a mast-cell stabilizer and a selective H₁-receptor antagonist and has been shown to be useful in the treatment of patients with allergic conjunctivitis. The ophthalmic formulation of ketorolac, a nonsteroidal anti-inflammatory drug, is marketed for the treatment of itching caused by seasonal allergic conjunctivitis, but it can produce irritation on instillation and may be less effective than mast-cell stabilizers or H₁-receptor antagonists. Long-term use of ophthalmic corticosteroids may cause cataracts and increase intraocular pressure, and is indicated only in the treatment of patients with severe allergic reactions (see the accompanying table).

Neither ketotifen, pemirolast or nedocromil result in significant absorption or accumulation of drug. Results of one four-week clinical trial revealed that ketotifen 0.05 percent was as effective as cromolyn 2 percent in decreasing the signs and symptoms associated with allergic conjunctivitis. Evidence from another clinical trial revealed that pemirolast 0.1 percent used four times daily was more effective (during the second 30 days of treatment) than placebo in preventing signs and symptoms of allergic conjunctivitis. Evidence from another trial involving patients with allergic conjunctivitis who took pemirolast 0.1 percent for four months revealed that pemirolast was more effective than placebo after six to eight weeks of treatment. Results from several double-blind studies showed that nedocromil 2 percent was more effective than placebo in the treatment of itching associated with allergic conjunctivitis. As with other mast-cell stabilizers, response to treatment with pemirolast or nedocromil may require weeks of treatment, although some patients detect a reduction of symptoms in a few days.

Ocular irritation, burning or stinging may occur with the use of these drugs. Conjunctival injection, headache and rhinitis were common side effects associated with the use of ketotifen, although allergic reactions, stinging, discharge, eye pain and photophobia occurred in less than 5 percent of patients. With pemirolast, the most common adverse side effects were headache, rhinitis and mild cold or flu symptoms. Headache was the most common adverse side effect associated with the use of nedocromil, but unpleasant taste and nasal congestion also occurred.

The consultants conclude that ketotifen, pemirolast and nedocromil appear to be effective in the treatment of itching caused by allergic conjunctivitis. Whether these drugs are more effective than the existing drugs in their class has not been determined.