What is the effect of minoxidil?
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The Effect of Minoxidil on Hair Growth and Hypertension
Minoxidil and Hair Growth: Mechanisms and Efficacy
Mechanisms of Action in Hair Follicles
Minoxidil is widely recognized for its ability to treat androgenetic alopecia (AGA) by promoting hair growth. The drug acts through multiple pathways, including vasodilation, anti-inflammatory effects, and the induction of the Wnt/β-catenin signaling pathway. It also functions as an antiandrogen and may affect the length of the anagen (growth) and telogen (resting) phases of hair follicles .
Research has shown that minoxidil directly increases the proliferation of dermal papilla cells (DPCs) in human hair follicles. This is achieved by activating extracellular signal-regulated kinase (ERK) and Akt pathways, which are crucial for cell survival and proliferation. Minoxidil also increases the expression of the anti-apoptotic protein Bcl-2 while decreasing the pro-apoptotic protein Bax, thereby promoting cell survival and hair follicle elongation.
Clinical Efficacy in Hair Regrowth
Topical minoxidil is available in various formulations, including 5% foam, 5% solution, and 2% solution, and is FDA-approved for both men and women with AGA. Clinical studies have demonstrated that minoxidil can cause hair regrowth in both the frontotemporal and vertex areas of the scalp. In a five-year study, 2% minoxidil showed peak hair growth in males at year one, although the efficacy declined in subsequent years.
Oral minoxidil, although not FDA-approved for hair loss, has shown promising results. A daily dose of 5 mg was found to be significantly more effective than topical formulations in male AGA. Low-dose oral minoxidil (0.5–5 mg/day) has also been effective for female pattern hair loss and chronic telogen effluvium.
Side Effects and Considerations
The most common side effects of topical minoxidil include irritant and allergic contact dermatitis on the scalp. Increased hair shedding can occur initially due to the synchronization of the hair cycle induced by the treatment. Oral minoxidil can cause systemic side effects such as hypertrichosis, lower limb edema, postural hypotension, and tachycardia .
Minoxidil as an Antihypertensive Agent
Mechanisms of Action in Hypertension
Minoxidil was initially introduced as an oral medication for severe hypertension. It acts as a potent vasodilator by opening potassium channels, which leads to the relaxation of vascular smooth muscle and a subsequent decrease in blood pressure. This vasodilatory effect is primarily due to the action of its sulfated metabolite, minoxidil sulfate .
Clinical Efficacy in Hypertension
Minoxidil has been effective in controlling blood pressure in patients with severe hypertension that is resistant to other antihypertensive drugs. In a study involving uremic patients with severe hypertension, the addition of minoxidil to their existing therapy resulted in a significant reduction in blood pressure without causing orthostatic hypotension.
Side Effects and Considerations
The use of minoxidil for hypertension is often accompanied by side effects such as fluid retention, which can lead to peripheral edema and, in severe cases, congestive heart failure. Hypertrichosis is another common side effect, which limits its acceptability, especially in female patients.
Conclusion
Minoxidil is a versatile drug with significant effects on both hair growth and hypertension. Its ability to promote hair regrowth through multiple pathways makes it a valuable treatment for androgenetic alopecia. However, its use is associated with various side effects, particularly when administered orally. As an antihypertensive agent, minoxidil is effective in managing severe, refractory hypertension but requires careful monitoring due to its potential side effects.
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