The availability of potent antihypertensive drugs that will decrease markedly elevated blood pressure within minutes to hours has changed the concepts of definition and therapy of hypertensive emergencies and urgencies. Intravenous infusion of sodium nitroprusside can be used in the truly emergent situation and is effective, reliable, and safe. While oral therapy is more convenient, it is not as consistently effective as parenteral administration and can lead to excessive reductions in blood pressure that are more difficult to manage than when short-acting agents are given intravenously.
Gifford R. Management of Hypertensive Crises. JAMA. 1991;266(6):829–835. doi:10.1001/jama.1991.03470060091033