Is Hydralazine a Diuretic?
No, hydralazine is not a diuretic—it is a direct arterial vasodilator used to treat hypertension and heart failure. 1
Drug Classification and Mechanism
Hydralazine belongs to the class of direct vasodilators, not diuretics. 1 The American Heart Association clarifies that hydralazine causes direct arterial vasodilation with minimal venous effects, which is fundamentally different from diuretic mechanisms that promote sodium and water excretion. 2
Key Distinguishing Features
Why Hydralazine Is NOT a Diuretic:
Mechanism of action: Hydralazine directly relaxes arterial smooth muscle, decreasing afterload and improving cardiac output, rather than promoting fluid excretion through the kidneys. 3
Clinical effects: The drug is associated with sodium and water retention and reflex tachycardia—the opposite of what diuretics do. 1
Required combination therapy: Because hydralazine causes fluid retention, the ACC/AHA guidelines explicitly state it should be used with a diuretic and beta blocker to counteract these effects. 1
Important Clinical Implications:
Hydralazine actually requires concomitant diuretic therapy when used for hypertension or heart failure because it promotes fluid retention through its vasodilatory effects. 1 This is a critical distinction—if hydralazine were a diuretic, it would not cause the compensatory sodium and water retention that necessitates adding an actual diuretic to the regimen.
Typical Clinical Use
In resistant hypertension management, the AHA recommends adding hydralazine at Step 5 of the treatment algorithm (after optimizing diuretics, RAS blockers, calcium channel blockers, mineralocorticoid receptor antagonists, and beta blockers). 1 This positioning further demonstrates that hydralazine serves a distinct role from diuretics in the treatment hierarchy.
For heart failure with reduced ejection fraction, hydralazine is combined with isosorbide dinitrate (not a diuretic either) to provide complementary vasodilation—hydralazine for arterial dilation and the nitrate for venous dilation. 1, 2, 4