Efficacy of combining timolol with other antiglaucoma medications

The ocular hypotensive effects of timolol and a carbonic anhydrase inhibitor (acetazolamide or methazolamide) are partially additive; that is, concurrent administration of these drugs produces a clinically useful reduction in intraocular pressure which is greater than the effect of either medication alone, but less than the arithmetic sum of the effects of the individual drugs. Similarly, concurrent administration of timolol and a miotic agent (pilocarpine, carbachol, or echothiophate iodide) produces a clinically useful response in most glaucoma patients. In contrast, the ocular hypotensive effects of timolol and epinephrine are poorly additive. Only a minority of patients maintain a substantial, longterm reduction in intraocular pressure when timolol is added to a regimen of epinephrine or vice versa. Ophthalmologists prescribing timolol or epinephrine for patients receiving the other drug are urged to use a therapeutic trial to one eye for several weeks to determine the efficacy of concurrent treatment. The addition of timolol to the medical regimen of patients uncontrolled on maximum tolerated antiglaucoma therapy (a miotic agent, epinephrine and a carbonic anhydrase inhibitor) reduces intraocular pressure substantially in one-third to one-half of the cases.