Since labetalol is used in patients with severe hypertension and chest pain, why is this agent considered dangerous in patients with cocaine-induced hypertensive emergency?
—Jose T. Lorenzo, MD, Millersburg, Ky.
The hypertension and coronary spasm induced by cocaine is at least partially mediated by stimulation of the sympathoadrenal system. In treating these effects, as in treatment of any adrenergic crisis, such as pheochromocytoma or clonidine withdrawal, one seeks balanced alpha and beta blockade since beta blockade by itself could result in unopposed alpha-receptor-mediated vasospasm, further aggravating the vasoconstriction. IV labetalol provides both alpha and beta blockade and appears to be useful in these situations. However, oral labetalol is less bioavailable and does not always provide effective alpha blockade. Hence there is concern about use of oral labetalol in these situations.
There are more data available on the use of alpha blockers, such as phentolamine, or vasodilators, such as nitroprusside, than there are for labetalol in these situations. I suspect IV labetalol is perfectly safe, but more data are needed to support that statement. Oral labetalol is more questionable and has the disadvantage of a slower onset of action; therefore, it cannot be recommended.
—Samuel J. Mann, MD (116-6)