Drug treatment for high blood pressure during pregnancy typically relies on a small number of medicines that have been shown -- by clinical research data -- to be safe for both the mother and the baby. Conversely, a large number of drugs used to treat high blood pressure are not generally safe for use during pregnancy, and a small number should be avoided completely.
Nitroprusside is an intravenous medicine sometimes used for short-term treatment of severe hypertension and is never given outside of a hospital. Nitroprusside can only be used for short periods of time because when the body breaks down the drug, a type of cyanide -- a deadly poison -- is produced. When the administration rate of nitroprusside is carefully monitored, this cyanide is eliminated from the body with no problems. But using the drug for long periods of time can lead to a toxic cyanide buildup. The body's normal ways of dealing with the cyanide produced from nitroprusside breakdown are less effective during pregnancy, increasing the risk of cyanide buildup. Additionally, even tiny amounts of cyanide can be toxic for the baby.
While most calcium channel blockers are safe for use during pregnancy, the fast-acting form of nifedipine should be avoided. Unlike nitroprusside, nifedipine has no inherent toxic effects. Instead, research data has shown that fast acting forms of the drug are more likely to cause sudden drops in blood pressure to levels that are below normal. In some emergency cases, this risk is worth taking because nifedipine is effective at quickly reducing blood pressure. In pregnant women, though, a sudden blood pressure decrease can interfere with blood flow to the baby -- a dangerous and potentially life-threatening situation.
ACE inhibitors should not be used at any stage of pregnancy. ACE inhibitors work by affecting the production of certain hormones made by the kidneys. A wealth of evidence has conclusively shown that these drugs pose serious risks to the health of the fetus. It was once thought that ACE inhibitors could be used with relative safety in the early stages of pregnancy. But later research found that they raise the risk of birth defects and affect the normal development of the heart. In the later stages of pregnancy, ACE inhibitors disrupt the proper functioning of the baby's kidneys, which can cause lung problems, abnormal limb development, and a decrease in the amount of amniotic fluid.
Shotan, A, Widerhorn, J, Hurst, A, Elkayam, U. Risks of angiotensin-converting enzyme inhibition during pregnancy: Experimental and clinical evidence, potential mechanisms, and recommendations for use. Am J Med 1994; 96:451.
Saji, H, Yamanaka, M, Hagiwara, A, Ijiri, R. Losartan and fetal toxic effects. Lancet 2001; 357:363.
Martinovic, J, Benachi, A, Laurent, N, et al. Fetal toxic effects and angiotensin-II-receptor antagonists. Lancet 2001; 358:241.
Guron, G, Friberg, P. An intact renin-angiotensin system is a prerequisite for normal renal development. J Hypertens 2000; 18:123.