Minoxidil
Minoxidil
Generic Name
Minoxidil
Mechanism
Minoxidil is a vasodilator that was first approved as an oral antihypertensive. Its hair‑growth properties arise from a different pharmacodynamics profile:
• Potassium channel opener: Activates ATP‑dependent K⁺ channels in dermal papilla cells, causing hyperpolarization and vasodilation.
• Prolonged follicular growth phase: Enhances the anagen phase of hair follicles, increasing follicular size and stimulating the transition of telogen hairs to anagen.
• Increased dermal papilla cell proliferation: Promotes angiogenic factor release and fibroblast activity, augmenting follicular nourishment.
• Stimulation of androgen‑independent growth: Works irrespective of dihydrotestosterone (DHT) levels, making it useful in both androgenetic alopecia (AGA) and telogen effluvium.
Pharmacokinetics
- Topical: Poor systemic absorption (≈ 5 % after 2 hours). 1–2 % of the applied dose reaches systemic circulation via dermal penetration.
- Oral (hypertension):
- Absorption: ~ 80 % bioavailability.
- Distribution: Protein‑bound (~ 10 %) with extensive tissue distribution.
- Metabolism: Primarily hepatic by CYP3A4 to an inactive metabolite, N‑oxide.
- Elimination: Renal excretion; renal clearance ~ 2.7 L/h; terminal half‑life ~ 3–4 h (shorter than expected due to active metabolites).
- Drug interactions: Inhibition by quinidine, CYP3A4 inducers (rifampin) can lower plasma levels; co‑administration with calcium channel blockers (e.g., diltiazem) may potentiate hypotension.
Indications
- Topical
- *Androgenetic alopecia* (male & female) – 5 % solution or foam for men; 2 % solution or foam for women.
- *Telogen effluvium* and *pattern hair loss* when first‑line options (finasteride, dutasteride) are contraindicated or ineffective.
- Oral (approved for hypertension) – reserved for refractory hypertension or resistant cases.
- Off‑label use in scalp and facial hypertrichosis, acne (rare), and post‑chemotherapy alopecia (clinical trials).
Contraindications
- Contraindications
- Severe cardiac failure (exacerbated fluid retention).
- Pregnant or lactating women (unknown fetal effects).
- Hypersensitivity to minoxidil or any excipient.
- Warnings
- Systemic absorption may cause hypotension, tachycardia, facial flushing, or edema.
- Use with caution in patients on β‑blockers or diuretics (altered hemodynamics).
- Avoid in patients using other topical vasodilators (e.g., nitroglycerin patches) to prevent additive hypotension.
- Dermal irritants (acetone, alcohol) should be avoided during application.
Dosing
| Form | Population | Dose | Frequency | Notes |
| 5 % topical solution (foam) | Male AGA | 1 mL (≈ 1 g) per application | Bid | Apply to dry scalp, allow to dry for 2 h, avoid excessive washing. |
| 2 % topical solution (foam) | Female AGA | 1 mL per application | Bid | Lower concentration reduces irritation; some use 1 x/day. |
| 5 % topical foam | Female AGA | 1 g (half‑tablet) | Bid | Foam formulation improves adherence, less scalp irritation. |
| Oral | Hypertension (rare) | 1–10 mg PO daily | Monitored in clinic | Start low; titrate to effect; monitor BP and electrolytes. |
| Combination (minoxidil + finasteride) | Male AGA | Same as monotherapy | Same | Combined therapy yields higher efficacy. |
Application technique tips
• Apply to a dry, clean scalp.
• Use a spray or foam to avoid over‑application.
• Wash hands after use; avoid contact with eyes, mucosal surfaces.
• Use a night‑time application if daytime application causes dizziness.
Adverse Effects
Common
• Scalp irritation, itching, dryness.
• Hypertrichosis (excessive body hair) – dose‑related.
• Facial flushing and warmth.
• Dizziness or light‑headedness (systemic absorption).
Serious (rare)
• Hypotension, tachycardia (especially with oral formulations).
• Edema (peripheral).
• Heart failure exacerbation.
• Allergic reactions: rash, urticaria, angioedema.
• Drug‑induced lupus (very rare).
Monitoring
- Blood pressure weekly until stable (≥ 4 weeks).
- Heart rate concurrently; check for tachycardia.
- Weight (for fluid retention).
- Scalp exam: monitor for dermatitis, follicular changes.
- Adherence: self‑report or diary.
- Hair growth progress: clinical evaluation every 3–6 months (photographs).
- Laboratory: baseline CBC, electrolytes, liver and kidney function when starting oral therapy or if systemic absorption suspected.
Clinical Pearls
- Start early: Initiate minoxidil within 12 months of hair loss onset for maximal benefit; later stages show diminishing returns.
- Foam reduces irritation: Foam formulations have lower solvent content, improving skin tolerability—particularly in women who experience more scalp sensitivity.
- “Two‑pills” rule: For men using 5 % solution, apply 1 g twice daily; applying more than 2 g per day offers no additional benefit and increases systemic risk.
- Avoid “over‑use”: Do not apply more than the recommended dose; excess can precipitate hypotension in rare cases.
- Pregnancy & breastfeeding: Minoxidil is category C; avoid during pregnancy or lactation unless benefits outweigh risks and no alternative exists.
- Combining with finasteride: The synergistic effect can lead to > 50 % improvement in hair count; however, monitor for sexual dysfunction from finasteride.
- Systemic absorption signs: Dizziness, palpitations, or facial flushing—if present, consider reducing dose or switching to topical foam.
- Patient education: Emphasize consistent daily use; hair regrowth can take 4–6 months, and discontinuation often results in rapid reversal of gains.
- Use of alcohol or acetone: These solvents can disrupt the drug’s absorption; instruct patients to keep their scalp free of these substances during the treatment period.
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• *References are available upon request. Use this card as a quick-reference guide for evidence‑based management of alopecia with minoxidil.*