Timoptol Mechanism of Action

TIMOPTOL (timolol maleate) reduces elevated and normal intraocular pressure whether or not associated with glaucoma. Elevated intraocular pressure is a major risk factor in the pathogenesis of glaucomatous visual field loss. The higher the level of intraocular pressure, the greater the likelihood of glaucomatous visual field loss and optic nerve damage.
Onset of action of TIMOPTOL is usually rapid, occurring approximately 20 minutes after topical application to the eye. Maximum reduction of intraocular pressure occurs in one to two hours. Significant lowering of intraocular pressure has been maintained for as long as 24 hours with 0.25 percent or 0.5 percent Ophthalmic Solution TIMOPTOL. This extended duration of action permits control of intraocular pressure over the usual sleeping hours. Repeated observations over a period of three years indicate that the intraocular pressure-lowering effect of TIMOPTOL is well maintained.
Timolol maleate is a nonselective β-adrenergic receptor blocking agent that does not have significant intrinsic sympathomimetic, direct myocardial depressant, or local anesthetic (membrane-stabilizing) activity.
The precise mechanism of action of TIMOPTOL in lowering intraocular pressure is not clearly established at this time, although a fluorescein study and tonography studies indicate that the predominant action may be related to reduced aqueous formation. However, in some studies a slight increase in outflow facility was also observed.
Unlike miotics, TIMOPTOL reduces intraocular pressure with little or no effect on accommodation or pupil size. Thus, changes in visual acuity due to increased accommodation are uncommon, and dim or blurred vision and night blindness produced by miotics are not evident. In addition, in patients with cataracts the inability to see around lenticular opacities when the pupil is constricted by miotics is avoided. When changing patients from miotics to TIMOPTOL a refraction might be necessary when these effects of the miotic have passed.
In clinical studies TIMOPTOL was generally effective in more patients and produced fewer and less severe side effects than either pilocarpine or epinephrine.
As with the use of other antiglaucoma drugs, diminished responsiveness to TIMOPTOL after prolonged therapy has been reported in some patients. However, in clinical studies in which 164 patients have been followed for at least three years, no significant difference in mean intraocular pressure has been observed after initial stabilization.
TIMOPTOL has also been used in patients with glaucoma wearing conventional hard contact lenses, and has generally been well tolerated. TIMOPTOL has not been studied in patients wearing lenses made with materials other than polymethylmethacrylate.