Levobunolol 3-antagonist

Nadolol is noteworthy for its very long duration of action its spectrum of action is similar to that of timolol. Timolol is a nonselective agent with no local anesthetic activity. It has excellent ocular hypotensive effects when administered topically in the eye. Levobunolol (nonselective) and betaxolol (E -selective) are also used for topical ophthalmic application in glaucoma the latter drug may be less likely to induce bronchoconstriction than nonselective antagonists. Carteolol is a nonselective 13-receptor antagonist. 

The potential ocular hypotensive effects of P-adrenoceptor antagonists (P-blockers) were first evaluated in the 1970s. This section highlights five agents currently marketed in the United States timolol, levobunolol, betaxolol, metipranolol, and carteolol (Table 10-1). 

Carteolol is a noncardioselective P-blocker similar to timolol, levobunolol, and metiptanoloLAs with levobunolol and metipranolol, a primary metaboUte of carteolol, 8-hydroxycarteolol, is also an ocular P-blocker. In contrast to other topical P-adrenoceptor antagonists, carteolol possesses intrinsic sympathomimetic ISA.The mechanism of carteolol s ocular hypotensive effect is a reduction in aqueous humor production, without any apparent effect on outflow. 

Beta-blockers that are available as eye-drops include timolol, metipranolol, and levobunolol, which are non-selective betai- and beta2-adrenoceptor antagonists, and betaxolol, a relatively cardioselective betai-adrenoceptor antagonist. Although selective betai-blockers are less likely to precipitate bronchospasm, this and other systemic effects can nevertheless occur (SED-12,1200). 

The J3 receptor antagonists are the next most common topical medical treatment. There are two classes of topical J3 blockers. The nonselective ones bind to both j3j and p2 receptors and include timolol, levobunolol, metipranolol, and carteolol. There is one pj-selective antagonist, betaxolol, available for ophthalmic use. It is less likely to cause breathing difficulty than nonselective 15 blockers, but it is less efficacious than the nonselective j5 blockers since the j5 receptors of the ciliary body epithelium and ocular blood vessels are 75—90% p2 subtype. The molecular basis of 15 blockade leading to decreased aqueous production and reduced lOP is uncertain. 

In spite of the fact that nearly complete /3-antagonistic activity resides in one enantiomer, propranolol and most of other /3-blockers are applied in the therapy as racemic mixtures. The only exceptions are levobunolol, timolol, and penbutolol used as the (S) enantiomers. 

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