Drug reference

Minoxidil

Potassium channel opener / peripheral vasodilator (oral); Hair growth stimulant (topical) · Antihypertensive

START

Oral: 2.5 mg BD with loop diuretic and beta-blocker (mandatory to prevent fluid retention and reflex tachycardia). Topical: 1 mL BD to dry scalp; 3-6 months before assessing response

TYPICAL MAX

Oral: 100 mg/day; Topical: 2 mL/day

STOP IF

Oral: pericardial effusion, angina, uncontrolled tachycardia. Topical: severe irritation, allergic reaction, no response after 6 months

WATCH

Oral: weight, edema, HR, BP, ECG (pericardial effusion), Hct (fluid hemodilution). Topical: scalp irritation, unwanted hair growth

CDSCO approvedATC C02DC01 (oral); D11AX01 (topical)

Dose laddermg/d

Renal dose adjustmenteGFR mL/min/1.73m²

KDIGO 2024 + manufacturer label

Pharmacokineticsplasma · t hours

ONSET: 30min · Oral: 30 minutes
PEAK: 2h · Oral peak
t½: 4.2h · 4.2 hours
DURATION: 1d · 24-hour BP control (BD dosing)

EXCRETION

Renal (90%, metabolites)

route + CYP

INTERACTIONS

2 major

SEVERE in our sources

PREGNANCY

Oral: Contraindicated in pregnancy; Topical: avoid in pregnancy (limited data)

FDA category + note

Top interactionssee all 12 →

GuanadrelSevereDatabaseDDInter
TizanidineSevereDatabaseDDInter

Available in India

221 branded formulations and 30 fixed-dose combinations. Look up specific brands in the Drugs workspace.

Mechanism

Oral: Opens ATP-sensitive potassium channels (KATP) on vascular smooth muscle, causing hyperpolarization and relaxation, leading to potent arterial vasodilation and BP reduction. Topical: Prolongs anagen phase of hair follicle cycling, increases follicular blood flow, and upregulates vascular endothelial growth factor (VEGF); mechanism not fully understood.

Indications

Oral: Severe hypertension refractory to other antihypertensivesTopical: Androgenetic alopecia (male and female pattern hair loss)Topical: Alopecia areata (off-label)

Dosing

Adult: Oral: 2.5-5 mg BD (max 100 mg/day). Topical: 1 mL of 2% (women) or 5% (men) solution applied to affected scalp BD; or half-capful of foam BD
Pediatric: Oral (<12 years): 0.1-1 mg/kg/day in divided doses. Topical: not recommended under 18 years
Renal adjustment: No adjustment needed; hepatically metabolized
Hepatic adjustment: No adjustment needed; active metabolite is not hepatically metabolized further
Geriatric: Start low; increased risk of orthostatic hypotension and reflex tachycardia
Max dose: Oral: 100 mg/day; Topical: 2 mL/day (5% solution)

Pharmacokinetics

Onset

Oral: 30 minutes; Topical hair growth: 3-6 months

Peak effect

Oral: 1-3 hours; Topical systemic absorption: minimal

Duration

Oral: 24-48 hours; Topical: continuous application needed

Half-life

4.2 hours (oral)

Bioavailability

Oral: ~95%; Topical: <2% systemic absorption

Protein binding

Minimal

Metabolism

Hepatic glucuronidation to active metabolite minoxidil sulfate (by SULT1A1)

Excretion

Renal (90%, primarily as metabolites)

Contraindications

Pheochromocytoma (can cause paradoxical hypertension)
Hypersensitivity to minoxidil
Pulmonary hypertension associated with mitral stenosis (oral)
Acute MI / dissecting aortic aneurysm

Side effects

Common

Oral: Tachycardia, palpitations, fluid retention, edema, hypertrichosisTopical: Scalp irritation, itching, dryness, initial increased hair shedding

Serious

Oral: Pericardial effusion / tamponade
Oral: Angina / myocardial ischemia (reflex tachycardia)
Oral: Pulmonary hypertension
Topical: Allergic contact dermatitis
Topical: Unwanted facial hair growth
Topical: Dizziness (if significant systemic absorption)

Pregnancy & lactation

Pregnancy

Oral: Contraindicated in pregnancy; Topical: avoid in pregnancy (limited data)

Lactation

Oral: excreted in breast milk; avoid. Topical: minimal systemic absorption; likely compatible but caution advised

Drug interactions

Guanadrel

Severe

Database

Clinical effect not specified

Source: DDInter

Tizanidine

Severe

Database

Clinical effect not specified

Source: DDInter

Betaxolol

Moderate

Textbook

Prevents or reduces palpitation and increased cardiac output.