Hydroquinone topical
Hydroquinone
Generic Name
Hydroquinone
Mechanism
* Tyrosinase inhibition – Hydroquinone competitively inhibits the rate‑limiting step of melanin synthesis by blocking the oxidation of tyrosine to dopaquinone.
* Melanosome inhibition – Reduces melanosome formation and causes premature degradation of existing melanin.
* Potentiation by light – Sunlight enhances penetration and accelerates depigmentation when combined with topical sunscreen.
Pharmacokinetics
* Absorption – Poor systemic absorption when applied at standard concentrations (≤10%); most remains in the epidermis.
* Metabolism – Hydroquinone is reduced to leucobenzoquinone in vivo; minor oxidation to 4‑hydroxy‑1,1‑dimethylaniline can occur.
* Elimination – Excreted mostly in urine unchanged; negligible biliary excretion.
* Half‑life – Local half‑life in skin is ~12–18 h; systemic serum half‑life <2 h if absorbed.
Indications
* Post‑inflammatory hyperpigmentation (PIH)
* Melasma (estrogen‑driven or post‑partum)
* Solar lentigines and seborrheic keratoses (mild discoloration)
* Café‑au‑lait–like patches in acquired hyperpigmentation disorders
* Cosmetic depigmentation when combined with sunscreen
Contraindications
* Known hypersensitivity to hydroquinone or any excipient.
* Active skin infections, lesions, or eczema at application sites.
* Pregnancy & lactation – Category C; use only if benefits outweigh risks.
* **Children 2% concentration.
* Risk of exogenous ochronosis – Avoid >10% concentration or >30 days continuous use; discontinue immediately if darkening or bluish discoloration occurs.
* Ocular proximity – Prevent accidental contact; can cause irritation or cataract progression.
Dosing
| Concentration | Application Frequency | Duration | Special Notes |
| 4‑10 % (OTC) | Once daily in the evening, leave on skin 8–10 h, wash off | Up to 4 weeks; then reassess | Use gentle cleansers; avoid vigorous scrubbing. |
| 10–20 % (Prescription) | Twice daily (morning & night) or once daily | Up to 8 weeks; taper off | Prescribe sunscreen ≥SPF 30 concurrently. |
| Adjunctive agents | Combine with tretinoin (0.05–0.1 %) for synergistic depigmentation | Same as above | Rotate application (alternate nights) to reduce irritation. |
Application technique:
1. Cleanse and dry the area.
2. Apply a thin film (1–2 mg/cm²) over the pigmented skin only.
3. Do not apply to facial areas prone to dryness unless using a moisturizer.
4. Follow with broad‑spectrum sunscreen during daylight.
Adverse Effects
* Common (≤10 % incidence)
* Pruritus, burning, mild erythema
* Patch‑type contact dermatitis
* Dryness or scaling
* Serious (≤1 % incidence)
* Exogenous ochronosis – dark bluish discoloration, irreversible in severe cases
* Anaphylactic reactions in hypersensitive individuals
* Post‑treatment pigment dilution paradox (temporary hyperpigmentation)
Monitoring
* Weekly skin assessment for erythema, scaling, or early ochronosis.
* Mid‑treatment review (after 4 weeks) to gauge efficacy and adjust concentration.
* Sunscreen compliance – Evaluate patient education and use of topical SPF.
* Pregnancy test if indicated; check for emerging pregnancy.
* Lab monitoring not necessary unless systemic symptoms appear (fever, malaise).
Clinical Pearls
1. Start low, go slow: Begin with 4 % or lower, especially in sensitive skin; avoid “flash” depigmentation that can trigger ochronosis.
2. Adjunctive retinoids: Tretinoin or adapalene can open the follicular route, enhancing hydroquinone penetration while also improving skin texture.
3. Split‑regimen avoids irritation: Apply hydroquinone on non‑pigmented skin one day, pigmented area the next to reduce dermatitis.
4. Use of moisturizers: Cetirizine‑free, fragrance‑free emollients after washing help restore barrier function without compromising absorption.
5. Patch testing: In patients with eczema or psoriasis, perform a 48‑hour patch test before full‑body use.
6. Sunscreen as a cornerstone: OCHN (exogenous ochronosis) is almost always associated with inadequate photoprotection; enforce daily SPF 30‑50 for 12+ h.
7. Avoid in acneic or rosacea‑prone skin: Hydroquinone may exacerbate inflammation; consider alternative agents (azelaic acid, kojic acid).
8. Photoprotective footwear on the face: Small patches of hydroquinone can cause mild eye irritation; keep a barrier (e.g., cotton gloves) if working outdoors.
9. Patient reassurance: Depigmentation is usually gradual; realistic expectations reduce frustration and non‑adherence.
10. Record pigmentation indices: Use of a photographic series every 4 weeks provides objective measures for efficacy, and helps detect early ochronosis.
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• *This drug card is intended for educational purposes and should not replace clinical judgment or regulatory guidelines. Consult local formularies and drug‑labeling information for the latest safety updates.*