- Betaxolol (BETOPTIC, beta1 selective)
- Timolol (TIMOPTIC, TIMOPTIC XE, BETIMOL)
- Target tissues are the ciliary body epithelium and blood vessels where
- β 2 receptors account for 75% to 90% of the total population. Beta
- adrenergic receptors on the ciliary epithelium facilitate the secretion of
- aqueous humor. Blocking these receptors reduces the secretory activity
- and consequently reduces intraocular pressure. Additionally, beta
- blockers decrease ocular blood flow, which decrease the ultrafiltration
- responsible for aqueous production.
- Betaxolol is the only beta1-selective agent for ophthalmic use, it is less
- efficacious than the nonselective agents since the beta-receptors of the
- eye are mainly beta2, but betaxolol is less likely to exacerbate reactive
- airway disease or cause breathing difficulty.
- Enough timolol can be absorbed from the eye to cause
- bronchoconstriction (beta2 in lungs) and bradycardia (beta1 in heart) in
- susceptible patients. Topical timolol may interact with orally administered
- verapamil and increase the risk of heart block. Additional side effects
- include, lightheadedness, cold fingers and toes, insomnia, fatigue,
- depression, vivid dreams, hallucinations, sexual dysfunction; hair loss.
- Timolol is contraindicated in patients with obstructive pulmonary disease
- and those with congestive heart failure.