Minoxidil, adverse reaction

Dihydralazine and minoxidil (via its sulfate-conjugated metabolite) dilate arterioles and are used in antihypertensive therapy. They are, however, unsuitable for monotherapy because of compensatory circulatory reflexes. The mechanism of action of dihydralazine is unclear. Minoxidil probably activates K channels, leading to hyperpolarization of smooth muscle cells. Particular adverse reactions are lupus erythematosus with dihydralazine and hirsutism with minoxidil—used topically for the treatment of baldness (alopecia androg-enetica). 

A 2% minoxidil (Rogaine) solution has been approved by the FDA for treating alopecia. Minoxidil causes vasodilation. This increases cutaneous blood flow and stimulates hair-follicle growth. However, alopecia returns within 3 to 4 months after the patient stops using minoxidil. Systemic absorption of minoxidil is minimal and adverse reactions seldom occur. 

Although vasodilators are effective in lowering blood pressure, these drugs are associated with a number of adverse effects. Reflex tachycardia often occurs because baroreflex responses attempt to compensate for the fall in vascular resistance that these drugs produce. This side effect is analogous to the increased heart rate occurring when alpha blockers are used to decrease peripheral vascular resistance. Other common reactions include dizziness, postural hypotension, weakness, nausea, fluid retention, and headache. Minoxidil also increases hair growth on the face, ears, forehead,... 

---