MINOXIDIL

Clinical safety rating: safe

Animal studies have demonstrated safety

How it works

Minoxidil is a potassium channel opener that hyperpolarizes vascular smooth muscle cells, leading to vasodilation. In hair follicles, it promotes hair growth by increasing blood flow and prolonging the anagen phase, possibly through stimulation of prostaglandin synthesis.

What the body does with it

Metabolism	Primarily metabolized by conjugation with glucuronic acid in the liver (UDP-glucuronosyltransferases). Minor metabolites include sulfates.
Excretion	Renal: 90% as unchanged drug and metabolites; fecal: 10% via bile.
Half-life	Terminal elimination half-life: 4.2 hours; clinical context: may be prolonged in renal impairment (up to 18 hours), requiring dose adjustment.
Protein binding	Negligible (unbound fraction >99%); does not bind significantly to plasma proteins.
Volume of Distribution	2.5-3.5 L/kg; extensive distribution into tissues, including vascular smooth muscle.
Bioavailability	Oral: 90% (rapidly absorbed); Topical: approximately 1.5% systemic absorption from scalp; intravenous: 100%.
Onset of Action	Oral: within 30 minutes for hypertension; Topical: 2-4 weeks for hair regrowth, up to 6 months for visible effect.
Duration of Action	Oral: antihypertensive effect lasts 24 hours with once-daily dosing; Topical: sustained with continuous use; discontinuation leads to reversal of hair growth within 3-6 months.

Classification & Brands

Dosing & administration

Oral: 5-40 mg/day in 1-2 divided doses, starting at 5 mg/day and titrating upward; Topical: 1 mL of 2% or 5% solution twice daily.

Dosage form	TABLET
Renal impairment	GFR <10 mL/min: avoid or reduce dose by 50%; GFR 10-50 mL/min: caution with titration; no specific dose adjustment for mild-moderate impairment.
Liver impairment	Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: avoid or use with extreme caution.
Pediatric use	Oral: Initial 0.1-0.2 mg/kg/day, max 1 mg/kg/day; Topical: not recommended for children <12 years.
Geriatric use	Start at lower end of dosing range (2.5-5 mg/day oral) due to increased sensitivity and risk of hypotension; monitor fluid and electrolytes.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other antihypertensive drugs can have additive effects Can cause pericardial effusion and hypertrichosis.

Breastfeeding

Excreted in human milk; M/P ratio unknown. Limited data suggest low levels, but potential for adverse effects in infant (hypotension, hypertrichosis). Manufacturer advises to discontinue nursing or drug. Consider risk-benefit.

Teratogenic Risk

FDA Pregnancy Category C. First trimester: Animal studies show fetal abnormalities (skeletal malformations, umbilical hernia) at doses 5 times the human dose. Human data insufficient. Second and third trimesters: May cause fetal tachycardia, hypertrichosis, and potential hypotension. Risk of fetal bradycardia and oligohydramnios if maternal hypotension occurs. Not recommended unless benefit outweighs risk.

Warnings & precautions

■ FDA Black Box Warning

Minoxidil (oral) is indicated only for hypertension that is symptomatic or associated with target organ damage and is not manageable with other antihypertensives. Must be administered under close clinical supervision.

Side Effect Profile

Common Effects	androgenetic alopecia
Serious Effects

Absolute Contraindications

Pheochromocytoma. Oral minoxidil is contraindicated in patients with malignant hypertension not under close supervision. Topical: hypersensitivity to minoxidil or alcohol.

Clinical Precautions

Precautions

Pericardial effusion/tamponade, pulmonary hypertension, exacerbation of angina, fluid retention/edema, hypertrichosis (systemic use), hypotension. Systemic absorption from topical use may cause salt/water retention. Monitor renal function, electrolytes, and ECG.

Clinical Tips & Counseling

Drug interactions

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