Actions of dilevalol on adrenoceptors

It is not surprising that there has been a search for compounds that combine two useful antihypertensive properties. The expectation is that one such product will offer a simple once-a-day control of blood pressure in a large portion of the population who require drug therapy for their disease. The major disadvantages of the first drug in this class, labetalol, are its poor and variable bioavailability, its relatively short duration of action, and its ability to produce postural hypotension. Attempts to improve the pharmacokinetic deficiencies have given rise to adimolol, which has a prolonged action of up to 90 h in single-dose studies. Of more immediate clinical interest are carvedilol, celiprolol, and dilevalol, each of which appear to have a different mechanism of producing vasodilation. Dilevalol, one of the four isomers of labetalol, is said to form approximately 25% of racemic labetalol. In the pithed rat, both labetalol and dilevalol behave as competitive nonselective beta-blocking drugs but dilevalol, unlike labetalol, shows weak alpha-blocking activity yet produces a dose-dependent fall that is blocked by propranolol, indicating that the drug has a vasodilator action presumably mediated by a beta 2-agonist effect on beta-adrenoceptors. The presence of beta 2-adrenoceptor agonism of this degree makes this drug extremely interesting. Possible advantages include the ability to produce falls in peripheral resistance without significant postural hypotension, and beneficial metabolic effects and effects on plasma lipids compared with traditional beta-adrenoceptor blocking agents that tend to raise blood sugars, interfere with insulin release, lower HDL levels, and raise LDL triglycerides.