From the Guidelines
Minoxidil should be used as a last-line agent for treating hypertension (HTN) due to its significant side effect profile, and its use should be carefully considered in the context of resistant hypertension. The oral form of minoxidil is prescribed at a starting dose of 5 mg once daily, which can be gradually increased to 10-40 mg daily in divided doses if needed, as indicated in the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline for the prevention, detection, evaluation, and management of high blood pressure in adults 1. Minoxidil works as a potent vasodilator by opening potassium channels in vascular smooth muscle cells, causing blood vessels to relax and widen, thus reducing blood pressure.
When using minoxidil for hypertension, it should almost always be combined with a diuretic to prevent fluid retention and a beta-blocker to prevent reflex tachycardia, as these are common side effects, as noted in the resistant hypertension: detection, evaluation, and management: a scientific statement from the American Heart Association 1. Patients should be aware that minoxidil commonly causes hypertrichosis (increased body hair growth), which may be cosmetically concerning, especially for women. Other potential side effects include pericardial effusion, edema, and weight gain.
Some key points to consider when using minoxidil for HTN include:
- Minoxidil is typically used as a last-line agent due to its side effect profile
- The medication should be used in combination with a diuretic and beta-blocker to mitigate common side effects
- Patients should be monitored regularly for potential side effects, including hypertrichosis, pericardial effusion, edema, and weight gain
- Dosage adjustments should be made under medical supervision to ensure optimal blood pressure control and minimize adverse effects.
It's also important to note that minoxidil is more commonly known for its topical formulation used to treat hair loss, but the oral form remains an important option for resistant hypertension when other medications have failed, as discussed in the guideline 1 and the scientific statement 1.
From the Research
Minoxidil and Hypertension
- Minoxidil is an orally active vasodilator used for the treatment of severe hypertension 2.
- It is effective in combination with diuretics and beta-adrenergic blocking agents for more than 80% of patients whose blood pressure has been inadequately controlled with other antihypertensive drugs 2.
- Minoxidil is indicated in patients whose blood pressure cannot be controlled with conventional therapy, in persons with major adverse reactions to other drugs, and in patients who are candidates for bilateral nephrectomy for control of hypertension 2.
Mechanism of Action and Pharmacokinetics
- Vasodilatory agents, including minoxidil, cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO), or by inhibiting myosin light chain kinase 3.
- Minoxidil is a potassium channel opener, which is reserved for patients with moderately severe to severe hypertension that is refractory to other treatment 3.
Safety and Efficacy
- Low-dose oral minoxidil has been shown to have a favorable safety profile in patients with hypertension or arrhythmia, with systemic adverse effects detected in 6.8% of cases 4.
- Prior treatment with doxazosin or with three or more antihypertensive drugs was associated with a higher risk of discontinuation of low-dose oral minoxidil 4.
- Antihypertensive drugs, including minoxidil, have various mechanisms of action and side effects, and their choice depends on the type of hypertension and individual patient characteristics 5.
Comparison with Other Antihypertensive Agents
- A comparison of different antihypertensive agents, including calcium antagonists, angiotensin-converting enzyme inhibitors, beta-blockers, and diuretic agents, showed that ACE inhibitors augmented reactive hyperemia, an index of endothelium-dependent vasorelaxation, in patients with essential hypertension 6.
- Minoxidil, as a vasodilator, may have a different effect on endothelial function compared to other antihypertensive agents, but its specific effects on reactive hyperemia have not been directly compared in this study 6.