Hydralazine

Summary

Hydralazine is a cardiovascular drug with a variety of different clinical uses.

Clinically, hydralazine may be used to treat heart failure. In contrast to many other cardiac medications, hydralazine is safe for use during pregnancy. Hydralazine can also be used to lower blood pressure in the treatment of hypertension, and may even be given acutely to treat hypertensive emergencies. 

Mechanistically, hydralazine increases levels of cyclic GMP, which causes smooth muscle relaxation. This primarily occurs in smooth muscle that lines the walls of blood vessels, resulting in vasodilation that preferentially dilates arteries more than veins.  The vasodilation and lowering of blood pressure also serves to lower afterload on the heart.

Side effects patients may experience while taking hydralazine include headache, and a key side effect to remember is reflex tachycardia, a compensatory increase in heart rate that occurs due to hydralazine’s blood pressure lowering effects. To prevent reflex tachycardia, hydralazine is often co-administered with beta-blockers. Other side effects of hydralazine include edema or fluid retention as well as drug-induced lupus in rare cases. Hydralazine can also cause angina as a side effect. Since it can also worsen pre-existing chest pain, hydralazine is usually contraindicated in patients with pre-existing angina or coronary artery disease.

Key Points

• Hydralazine
  • Clinical Use
    • Treats Severe Hypertension (especially acute)
      • Can be used in hypertensive emergencies
        • Not first-line (outside of pregnant patients) due to short half-life and reflex tachycardia
    • Safe for Use During Pregnancy
      • First-line for treating gestational hypertension and pre-eclampsia / eclampsia
    • Treats Heart failure
      • Often given with a nitrate
      • Reducing afterload can increase stroke volume and cardiac output
  • Mechanism
    • Increases cyclic GMP (cGMP)
      • Causes smooth muscle relaxation
    • Vasodilator
      • Dilates Arteries >> Veins
    • Reduces Afterload
  • Side Effects
    • Drug-induced lupus
      • Causes lupus-like symptoms with +ANA and anti-histone abs
      • Increased risk in slow acetylators
    • Reflex tachycardia
      • Coadministered with a beta-blocker
        • To prevent reflex tachycardia
    • Angina
      • Contraindicated in angina / CAD
    • Fluid retention / edema
      • Often coadministered with a diuretic
    • Headache