ABSTRACT
Fixed combination therapies may enhance compliance and the quality of life by decreasing the number of instillations per day, maintaining the hypotensive efficacy with fewer drops. In general, combinations have to fulfill some requirements.The efficacy of a fixed combination of drug A and drug B has to be greater than drug A or drug B alone. Although a complete additive effect is not required by the FDA, the ideal fixed combination would have the same effect of the concomitant use of drug A and drug B. Several fixed combinations have been developed, including timolol-pilocarpine, epinephrine-pilocarpine, and betaxolol-pilocarpine. A fixed combination of dorzolamide 2% and timolol (Cosopt®) 0.5% is now commercially available in several countries. An experimental study in rabbits has shown that the ocular penetration of one drug is not affected by the other, leading to similar concentrations of dorzolamide and timolol in the ciliary body of rabbits after the instillation of the fixed combination and of both drugs individually.
