SCH 19927, the RR isomer of labetalol, has been shown to possess beta-blocking and vasodilator properties.It was compared to timolol for ability to lower intraocular pressure (IOP) in conscious rabbits.Its potential for systemic beta-blockade after topical administration was also assessed.Dose-related reductions in IOP followed topically applied SCH 19927 (0.1-1.0%). Timolol in concentrations less than 0.5% was not effective in lowering IOP. Timolol (0.1 and 0.5%) strongly inhibited tachycardia induced by iv isoproterenol. A 1.0% concentration of SCH 19927 was less effective than 0.5% timolol in inhibiting the isoproterenol-induced tachycardia; 0.1% SCH 19927 caused only minor inhibitory actions.Thus, not only is SCH 19927 at least as potent in lowering IOP in conscious rabbits, its topical administration results in less systemic beta-blockade than does timolol.
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