Beta-adrenergic antagonist are an important class of drugs for the treatment of various heart diseases, such as high blood pressure, insufficiency of blood flow to the heart muscle, irregular heart beat, thickened heart muscle, and decreased ability of the heart to empty or fill normally. β-Blockers can also be used to treat migraine headache and increased eye pressure (glaucoma). Carteolol is a nonselective beta-adrenoceptor antagonist.

In vitro: Previous findings demonstrate that carteolol, unlike xamoterol, is a nonconventional partial agonist, which causes agonistic effects via interaction with the low-affinity propranolol-resistant site of β1-adrenoceptors and antagonistic actions by the high-affinity site of the same receptors [1].

In vivo: Both 8-OH carteolol and carteolol suppressed the water-load induced intraocular pressure (IOP) rise in rabbits. 8-OH carteolol was more effective in suppressing water-load induced IOP rise in rabbits compared with carteolol on equimolar basis. Both 8-OH carteololand carteolol caused a significant decrease in IOP in monkeys. 8-OH carteolol was estimated to be more potent than carteolol in lowering IOP on equimolar basis in monkeys [2].

Clinical trial: The new alginate formulation of long-acting carteolol 1% given once daily is as effective as standard 1% carteolol given twice daily, with no meaningful differences regarding safety. The new alginate formulation of long-acting 1% carteolol given once a day is effective and well tolerated by glaucoma patients requiring chronic treatment [3].

Reference:
[1] Maura Floreani, Guglielmina Froldi, Luigi Quintieri, Katia Varani, Pier Andrea Borea, Maria Teresa Dorigo and Paola Dorigo.  In Vitro Evidence That Carteolol Is a Nonconventional Partial Agonist of Guinea Pig Cardiac β1-Adrenoceptors: A Comparison with Xamoterol. JPET 315:1386–1395, 2005
[2] Sugiyama K, Enya T, Kitazawa Y.  Ocular hypotensive effect of 8-hydroxycarteolol, a metabolite of carteolol. Int Ophthalmol. 1989 Jan;13(1-2):85-9.
[3] Trinquand C, Romanet JP, Nordmann JP, Allaire C; Groupe d'étude.  Efficacy and safety of long-acting carteolol 1% once daily. A double-masked, randomized study. J Fr Ophtalmol. 2003 Feb;26(2):131-6.