Hydralazine/isosorbide dinitrate (fixed combination)

Class

Direct vasodilator fixed-dose combination

This fixed-dose combination pairs two vasodilators that act through distinct mechanisms to reduce the workload of a failing heart. Hydralazine relaxes the smooth muscle of arterioles, the small resistance vessels that determine how hard the heart must contract to eject blood (afterload). Isosorbide dinitrate is a nitrate that is metabolized to release nitric oxide, which activates a signaling pathway leading to relaxation of veins, thereby lowering the volume of blood returning to the heart (preload). By reducing both the resistance the heart pumps against and the volume it must handle, the combination decreases cardiac strain and can improve symptoms in chronic heart failure with reduced pumping function. The two agents are combined because hydralazine partially offsets a limitation of nitrate therapy: repeated nitrate exposure can blunt its own effectiveness over time, and hydralazine's antioxidant-like effects appear to preserve nitric oxide activity, supporting more durable benefit than either drug used alone. This mechanism is broadly relevant in heart failure management, particularly in situations where other standard therapies affecting the renin-angiotensin system are not well tolerated or are insufficient alone.