Vasodilator Therapy

Vasodilators are medications that directly affect the smooth muscle of arteries and are used to treat hypertension. The most common direct-acting vasodilators are hydralazine and minoxidil. Alright, let’s focus on hydralazine.

Hydralazine relaxes the smooth muscle of the arteries by inhibiting intracellular calcium release within the smooth muscle cells, which inhibits its ability to contract, leading to vasodilation, decreased peripheral vascular resistance, and decrease in blood pressure.

Okay, so the side effects of hydralazine are mostly related to their vasodilatory effects, which cause hypotension; reflex tachycardia, where the sympathetic nervous system is stimulated to increase the heart rate in response to decreased peripheral vascular resistance and hypotension; flushing; headache; and dizziness. Other more serious side effects of hydralazine are related to sodium and water retention and include peripheral edema, pulmonary edema, and dyspnea. Although the mechanism of action is unclear, hydralazine can also cause lupus-like symptoms, such as malaise, myalgia, and fever.

Now, contraindications for use of hydralazine include certain cardiovascular diseases since a sudden drop in blood pressure and subsequent reflex tachycardia can lead to increased myocardial oxygen demand, angina, and myocardial infarction; and certain cerebrovascular diseases because vasodilation can increase cerebral blood flow, resulting in increased intracranial pressure. Hydralazine should also be avoided in patients with septic shock due to its vasodilatory effects.