So much variability exists when it comes to managing hypertension in the hospital. (J Clin Hypertens. 2010;12:698; https://bit.ly/3o3B64N.) Hydralazine, a potent vasodilator, is used throughout the United States as an intravenous drug to lower blood pressure, and it is often used off-label for hypertensive emergencies, although it has little evidence of improvement in results. Many problems with hydralazine should raise eyebrows among emergency physicians.
The usual side effects are often overlooked. Hydralazine is known to cause reflex tachycardia and headaches. A study of 2189 patients showed that 16% suffered from hypotension, dizziness, lightheadedness and headache after IV administration. (J Clin Hypertens. 2010;12:29; https://bit.ly/3DdlDDr.) It can also be harmful if given to the wrong patients, especially those with myocardial infarction or aortic dissection. (Clin Pharmacol Ther. 1983;34:148; https://bit.ly/3lhTHZd.)
Hydralazine is a bit like rolling the dice on blood pressure management. You don’t know when blood pressure will change or how low to expect it to drop. After administration, hydralazine has a latency period of five to 15 minutes before the onset of action, and after onset it can cause a sharp drop in blood pressure that can last up to 12 hours. (J Clin Invest. 1951;30:672; Clin Pharmacol Ther. 1980;28:804.) This is impractical for any clinician wanting a predictable drop in blood pressure. In fact, studies have shown that the circulating half-life of hydralazine is nearly three hours, but its blood pressure half-life is 12 hours, with some sources citing up to 100 hours.
A prospective study in 2010 analyzed 94 hospitalized patients receiving hydralazine. They tracked changes in blood pressure as well as indications for its use. Seventeen patients presented with hypotension. Overall, blood pressure changes were extremely variable, ranging from -35 + 25 mm Hg. (J Am Soc Hypertens. 2011;5:473; https://bit.ly/3xAZwG4.) Several studies carried out in other institutions confirm the conclusions that hydralazine causes a heterogeneous effect on blood pressure. (J Clin Hypertens. 2010;12:29; https://bit.ly/3DdlDDr.)
Not so benign
Hydralazine is not the right answer for pregnant patients with a hypertensive emergency. A meta-analysis demonstrated that it was shown not only to cause reflex tachycardia, but was more likely to cause delayed maternal hypotension and fetal bradycardia than any other antihypertensive agent. (BMJ. 2003;327:955; https://bit.ly/3pgc3ek.) It has also been associated with abdominal pain that can mimic preeclampsia. Many other safer and more effective agents can control blood pressure in pregnant patients.
Perhaps the perception is that hydralazine is a benign drug and one dose of hydralazine cannot be as harmful. Unfortunately, given its long half-life, adverse effects may not be recognized or related to hydralazine if they occur hours later, prompting the clinician to make poor, reactionary decisions.
Although its side effects are not understood, the indiscriminate use of hydralazine is reminiscent of the bad practice of treating numbers, not patients. Unfortunately, many doctors ignore any cognitive work and jump on a simple gut reaction: push IV drugs for immediate gratification. It was found in one study that only 7.5% of physicians assessed patients prior to hydralazine dosing and only 25% of patients had adjustments in their long-term medications. (J Am Soc Hypertens. 2011;5:473; https://bit.ly/3xAZwG4.) Quick change is better, right? Not really. It would be one thing to push labetalol IV, but hydralazine doesn’t give consistent results.
Instead of jumping to IV medications, take the time to talk to patients about their home blood pressure regimens. Make sure they haven’t missed any doses and consider treating a patient’s pain and nausea before mistakenly popping in to lower their blood pressure.
Countless studies have shown that overly aggressive management of uncomplicated asymptomatic hypertension with IV medications has no proven benefit and is potentially harmful. (JAMA. 2003;289:2560.) The use of hydralazine for hypertensive emergencies is simply irrational. We need treatments for critically ill patients that have rapid, predictable and tolerable effects. Hydralazine is broken, cannot be repaired, and certainly will not fix our sick patients.
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Dr. Briggsis an assistant professor of emergency medicine at the University of South Alabama in Mobile. He is the founder, podcast co-host and editor of EM Board Bombs (https://www.emboardbombs.com), a cross-platform educational tool designed to prepare for counseling and focus on what you need to know to practice emergency medicine. Follow him on Twitter@blakebriggsmd.