GENERIC NAME: timolol ophthalmic solution

BRAND NAME: Timoptic

DRUG CLASS AND MECHANISM: Timolol is a beta- adrenergic blocking agent. Like other beta-adrenergic blocking agents, it mainly blocks the action of the sympathetic (adrenergic) nervous system, for example, on the heart. In addition to its effect on the heart, timolol causes a reduction of the pressure within the eye (intraocular pressure). This effect is thought to be caused by a reduction in the production of the liquid (aqueous humor) within the eye. The precise mechanism of this effect is not known. The reduction in intraocular pressure reduces the risk of damage to the optic nerve and loss of vision in patients with glaucoma. Timolol was approved by the FDA for ocular use in 1978.

PRESCRIPTION: yes

GENERIC AVAILABLE: yes

PREPARATIONS: Ophthalmic solution: 0.25%, 0.5%. There is also a gel-forming solution (Timoptic-XE) in a 0.25% and 0.5% concentration.

STORAGE: Ophthalmic solution should be kept at room temperature, 15-30°C
(59-86°F) and protected for direct light.

PRESCRIBED FOR: Timolol is used for the treatment of glaucoma. (Oral timolol tablets are used for treating high blood pressure and angina, but this dosage form is not discussed here.)

DOSING: Both hands should be washed before each use of timolol or any other eye medication. The head should be tilted back and the lower lid pulled down with the index finger to form a pouch. The tip of the dropper should not be touched to the eye or eyelid. The bottle should be squeezed slightly to allow the prescribed number of drops into the pouch. The eye is closed gently for 1 to 2 minutes without blinking. The usual dose is one drop into the affected eye twice daily. Timoptic-XE gel forming solution usually is used once daily.

DRUG INTERACTIONS: Combined use of oral beta- adrenergic blocking agents, for example, propranolol (Inderal), atenolol (Tenormin), metoprolol (Lopressor) or carvedilol (Coreg) with ophthalmic timolol can result in additive effects. Thus, patients may experience excessively low blood pressure or reductions in heart rate.

PREGNANCY: Although there are no human studies that have examined the effects of oral timolol on the fetus, animal studies have shown adverse effects. Therefore, the physician must weigh the potential risks to the fetus against the potential benefits to the mother. It is unknown if the small amount of timolol that penetrates into the blood after administration into the eye affects the fetus.

NURSING MOTHERS: Concentrations of timolol in breast milk can be three times those in the mother's blood after oral administration. It is not known how much, if any timolol appears in breast milk after administration into the eye. Ideally, patients taking timolol should avoid breast-feeding.

SIDE EFFECTS: Ophthalmic timolol can cause irritation to the eye which may manifest as pain or dryness in some people. Rarely, timolol eye drops can result in side effects that are seen with other oral beta adrenergic blockers. For example, persons can experience fatigue, insomnia, nausea, slow heart rate, low blood pressure, cold extremities, and shortness of breath or wheezing.

Last Editorial Review: 5/11/1998

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