Minoxidil (Loniten) is a potent oral peripheral vasodilator primarily used for the treatment of severe, refractory hypertension.
Basic Drug Information and Mechanism of Action
1. Drug Properties
Minoxidil is a white or almost white crystalline solid, soluble in water, propylene glycol, and ethanol.
2. Mechanism of Action
(1) Minoxidil exerts its effect by directly acting on the smooth muscle of arterial blood vessels, causing relaxation and dilation. This significantly reduces peripheral vascular resistance, thereby lowering both systolic and diastolic blood pressure.
(2) The drug does not affect the vasomotor reflex, so orthostatic hypotension is not typically induced.
(3) Its antihypertensive effect triggers compensatory tachycardia and sodium/water retention. Therefore, clinical use requires concomitant administration of diuretics, beta-blockers, and other medications to counteract these adverse reactions.
3. Pharmacokinetics
(1) Orally administered minoxidil is well absorbed (≥90%), reaching peak plasma concentrations within approximately 1 hour, with an average half-life of about 4.2 hours.
(2) The drug is primarily metabolized in the liver; its metabolites have weak pharmacological activity and are mainly excreted via the kidneys.
Indications, Contraindications, and Key Warnings
1. Indications
(1) Only indicated for patients with symptomatic hypertension or hypertension with target organ damage who fail to achieve blood pressure control despite treatment with the maximum tolerated doses of a diuretic plus two other antihypertensive agents.
(2) Not recommended for the treatment of mild hypertension.
2. Contraindications
Minoxidil is contraindicated in patients with pheochromocytoma (as it may stimulate catecholamine secretion by the tumor) and in those with hypersensitivity to any component of the drug.
3. Key Warnings and Precautions
(1) Fluid Retention and Heart Failure: Minoxidil can cause significant sodium and water retention. Concomitant use of a potent diuretic (usually a loop diuretic such as furosemide) is mandatory to prevent heart failure. Close monitoring of body weight is required.
(2) Tachycardia and Angina: The drug induces reflex tachycardia, which may precipitate or exacerbate angina. Concomitant use of a beta-blocker or other sympathetic inhibitors is essential to control heart rate.
(3) Pericardial Disorders: There is a risk of pericarditis, pericardial effusion, and even cardiac tamponade, particularly in patients with renal insufficiency. Awareness of associated symptoms and performance of echocardiography when necessary are recommended.
(4) Drug Interaction with Guanethidine: Concomitant use in patients already receiving guanethidine may cause severe orthostatic hypotension. Guanethidine should be discontinued prior to initiating minoxidil if possible, or treatment should be initiated in a hospital setting.
(5) Rapid Blood Pressure Reduction: In patients with malignant hypertension, overly rapid blood pressure lowering may lead to ischemia of vital organs. Initial treatment should be conducted in a hospital, with slow dose titration.
Medication Guidance and Patient Instructions
1. Dosage and Administration
(1) Adults (≥12 years): The initial dosage is usually 5 mg once daily. Titrate gradually based on therapeutic response; the usual range is 10–40 mg/day, with a maximum dose of 100 mg/day.
(2) Children (<12 years): The initial dosage is 0.2 mg/kg/day, with gradual titration; the maximum dose is 50 mg/day.
(3) Dosing Adjustment Principle: Dose adjustments should be made at intervals of at least 3 days to achieve stable blood pressure reduction. For large reductions in blood pressure, the daily dose may be divided into two administrations.
2. Mandatory Concomitant Medications
(1) Diuretics: Such as hydrochlorothiazide, chlorthalidone, or furosemide, to control fluid retention.
(2) Heart Rate-Controlling Agents: Typically beta-blockers (e.g., propranolol); methyldopa or clonidine may be used if beta-blockers are contraindicated.
3. Patient Monitoring and Education
(1) Monitoring Parameters: Regular monitoring of blood pressure, heart rate, body weight, electrolytes, and renal function. Awareness of symptoms of pericardial effusion (e.g., chest pain, dyspnea) is important.
(2) Critical Warning Signs: Patients should be alert to and report the following immediately: sustained tachycardia (resting pulse rate increase ≥20 beats/min), rapid weight gain (>5 pounds) in a short period, dyspnea (especially when supine), new-onset or worsening chest pain, and severe dizziness or syncope.
(3) Hypertrichosis: Approximately 80% of patients will experience increased, thickened, and darkened body hair, typically appearing 3–6 weeks after treatment initiation. This effect is reversible within 1–6 months of drug discontinuation. Female and pediatric patients should be informed of this effect prior to treatment.
