Dorzolamide hydrochloride/timolol maleate

Opfitfialmic Solution-. 2% dorzolamide hydrochloride and 0.5% timolol maleate (Cosopt). 

In this case the allergic reaction was caused by dorzolamide hydrochloride and not the preservative, benzalkonium chloride, since therapy was uneventfully continued with timolol maleate, which also contains benzalkonium chloride as a preservative. This is the first report of this phenomenon with a carbonic anhydrase inhibitor. 

Eyes In a cohort study of 34 patients with either primary open-angle glaucoma (OAG) or ocular hypertension (HTN), use of dorzolamide hydrochloride 1%/timolol maleate 0.5% combination eye drops showed adverse reactions of stinging sensation (50% of patients), powder sticking aroxmd the eyes (14.7% of patients) and blurred vision (11.8% of patients) [8]. The mechanism of increasing sensations of buming/stinging is probably because of the low pH (e.g. dorzolamide/timolol fixed combination has a pH of 5.5-5.8) [8]. 

---