To report a case series of patients experiencing side effects of 0.25% alcaftadine eye drops and to analyze the possible reasons for the side effects.

Medical records of 90 patients who had a history of alcaftadine eye drop use were retrospectively analyzed. Eight out of the 90 patients (8.9%) showed ocular side effects that required discontinuation of the alcaftadine eye drops. All eight cases of alcaftadine side effects showed palpebral and bulbar conjunctival injection, watery discharge, and lid swelling. During additional history collection, all patients with alcaftadine side effects confessed of overuse (more than twice/day) of the eye drops. Anticipation for fast symptom relief was the main reason for the alcaftadine overuse. In all side effect cases, patients were asked to stop alcaftadine eye drops and use preservative-free artificial tears and steroid eye drops. After discontinuation of 0.25% alcaftadine eye drops, regression of palpebral and bulbar conjunctival injection and lid swelling was observed.

Overuse of 0.25% alcaftadine eye drops can induce ocular surface toxicity possibly due to toxicity of drug itself. The possible side effects of overuse of 0.25% alcaftadine eye drops should be fully explained to all patients before use.