From the Guidelines
Hydralazine works by directly relaxing the smooth muscle in arterial blood vessel walls, causing vasodilation, which leads to decreased peripheral vascular resistance and reduced blood pressure. This effect is achieved by interfering with calcium movement in vascular smooth muscle cells and possibly by increasing nitric oxide production, a natural vasodilator 1. The medication acts primarily on arteries rather than veins, making it particularly useful for treating hypertension.
Key Points
- Hydralazine is contraindicated in advanced aortic stenosis, patients with soybean, soy product, egg, and egg product allergy, and in patients with defective lipid metabolism 1.
- It is also contraindicated in patients with concurrent beta-blocker therapy, bradycardia, or decompensated heart failure, and may worsen heart failure 1.
- The medication can cause tachyphylaxis with extended use, and cyanide toxicity with prolonged use can result in irreversible neurological changes and cardiac arrest 1.
- Hydralazine is mainly useful in hypertensive emergencies associated with high plasma renin activity, and its dose is not easily adjusted 1.
- The therapeutic goal of using hydralazine is to minimize target organ damage safely by rapid recognition of the problem and early initiation of appropriate antihypertensive treatment 1.
Clinical Considerations
- When prescribing hydralazine, it is essential to monitor for bradycardia and to use low-end dose ranges for elderly patients 1.
- Intra-arterial BP monitoring is recommended to prevent "overshoot" and to adjust the dose accordingly 1.
- Hydralazine may worsen reactive airway disease or chronic obstructive pulmonary disease, and higher doses may block beta2 receptors and impact lung function 1.
From the FDA Drug Label
Although the precise mechanism of action of hydrALAZINE is not fully understood, the major effects are on the cardiovascular system. HydrALAZINE apparently lowers blood pressure by exerting a peripheral vasodilating effect through a direct relaxation of vascular smooth muscle HydrALAZINE, by altering cellular calcium metabolism, interferes with the calcium movements within the vascular smooth muscle that are responsible for initiating or maintaining the contractile state Hydralazine works by:
- Exerting a peripheral vasodilating effect through a direct relaxation of vascular smooth muscle
- Altering cellular calcium metabolism to interfere with calcium movements within the vascular smooth muscle
- Causing a decrease in arterial blood pressure (diastolic more than systolic) and peripheral vascular resistance, and an increase in heart rate, stroke volume, and cardiac output 2
From the Research
Mechanism of Hydralazine
- Hydralazine is a vasodilator that works by relaxing the muscles in blood vessel walls, causing the vessels to dilate 3.
- This dilation of blood vessels reduces blood pressure, as the heart does not have to work as hard to pump blood through the body 3.
- Hydralazine is often used in combination with other medications, such as beta blockers and diuretics, to treat high blood pressure 4, 5.
- In patients with heart failure, hydralazine may be used in combination with nitrates to improve symptoms and reduce mortality 6.
Comparison to Other Antihypertensive Medications
- Hydralazine has been compared to other antihypertensive medications, such as nifedipine, in terms of its effectiveness in reducing blood pressure 3.
- Studies have shown that hydralazine is effective in reducing systolic and diastolic blood pressure in patients with hypertension 3, 7.
- However, the effectiveness of hydralazine may vary depending on the individual patient and the specific medication regimen used 7.