PURPOSE: We evaluated the anterior segment surface reaction findings between timolol hemihydrate and timolol maleate. The only known difference between these preparations is the maleate salt.

METHODS: After a baseline examination, we randomized 28 healthy subjects (26 completed) to timolol hemihydrate or timolol maleate given in both eyes twice daily, in a double masked fashion, for 1 week. Subjects then were evaluated at the morning trough (hour 0 examination), dosed, and re-evaluated in 1 hour (hour 1 examination). Subjects were left untreated for 1 week and then switched to the opposite medication for the second study period.

RESULTS: Corneal staining (graded 0 to 4) for timolol maleate was worse between baseline (0.9) and hour 0 (1.4; P = .009) and baseline and hour 1 (1.4; P = .011). Also, mean punctate corneal staining for timolol maleate was increased from baseline (22.6) to hour 0 (31.7; P = .033) and showed borderline significance to hour 1 (33.4; P = .058), and for timolol hemihydrate there was a borderline significant elevation from baseline (24.2) to hour 1 (29.8; P = .060). When treatment groups were compared, there was a greater change in corneal staining with timolol maleate than timolol hemihydrate from baseline to hour 0 (P = .020) and greater staining with timolol maleate than timolol hemihydrate at hour 0 (P = .032). Nasal conjunctiva showed increased mean staining with timolol maleate from baseline (23.6, P = .035) to hour 0 (29.5, P = .035) and to hour 1 (31.9 P = .038) but not with timolol hemihydrate. There were increased symptoms of ocular dryness from baseline to hour 0 with timolol maleate (P = .012) but not with timolol hemihydrate.

CONCLUSIONS: The study suggests that timolol maleate potentially may have more of an irritant effect than timolol hemihydrate on the corneal and nasal conjunctival epithelium.