Products
Timolol is commercially available in the form of eye drops and as an eye gel. In addition to the original Timoptic, generics and various fixed combinations with other antiglaucomatous agents are also commercially available (brinzolamide, brimonidine, dorzolamide, travoprost, latanoprost). Timolol has been approved in many countries since 1978. See also under timolol gel (hemangioma).
Structure and properties
Timolol (C13H24N4O3S, 316.42 g/mol) is present in drugs as -timolol maleate, a white, odorless, crystalline powder or colorless crystals that are soluble in water. It is a thiadiazole and morpholine derivative and has a typical beta-blocker structure.
Effects
Timolol (ATC S01ED01) lowers intraocular pressure. It is a nonselective beta blocker at beta1 and beta2 adrenoceptors without local anesthetic or sympathomimetic properties. As such, it has the potential to constrict the bronchi and lower pulse rate and blood pressure, among other effects. The effects on the eye are based on a reduction in aqueous humor formation and an improvement in aqueous humor outflow.
Indications
For the treatment of elevated intraocular pressure (ocular hypertension) and for the treatment of glaucoma.
Dosage
According to the drug label. The usual dosage is 1 drop per diseased eye twice daily. There are also extended-release medications on the market that require administration only once daily. See also under Administering eye drops.
Contraindications
- Hypersensitivity
- Certain respiratory diseases (eg, bronchial asthma, COPD) and cardiovascular diseases (eg, low heart rate).
Full precautions can be found in the drug label.
Interactions
Interactions have been described with epinephrine, systemic beta blockers, CYP2D6 inhibitors, other antihypertensives, digoxin, and calcium channel blockers.
Adverse effects
Possible adverse effects include local reactions to the eye such as transient burning and stinging. Systemic adverse reactions, such as headache, decrease in heart rate, low blood pressure, bronchospasm, and fatigue, may occur due to absorption into the bloodstream.
