Topical Retinoids

Topical retinoids (tretinoin, adapalene, tazarotene, trifarotene, and isotretinoin gel) are vitamin A derivatives that normalise follicular keratinisation and are the foundation of acne treatment. They are also used for photoageing, hyperpigmentation and some scaling disorders.

Mechanism. Binding to nuclear retinoic acid receptors (RAR-alpha, beta and gamma; adapalene and trifarotene are selective for RAR-beta and gamma, and RAR-gamma respectively) changes gene expression: reduced keratinocyte cohesion and comedone formation, increased epidermal turnover, anti-inflammatory effect, and increased collagen synthesis.

Pharmacokinetics. Minimal systemic absorption (under 2 percent). Adapalene is photostable and does not degrade with benzoyl peroxide; tretinoin degrades in light and with benzoyl peroxide.

• Tretinoin 0.01 to 0.1 percent (cream, gel): best evidence for photoageing and acne; most irritant at high strengths.
• Adapalene 0.1 and 0.3 percent: best tolerated; also available fixed with benzoyl peroxide.
• Tazarotene 0.05 and 0.1 percent: most potent; also used for psoriasis; contraindicated in pregnancy.
• Trifarotene 0.005 percent: for truncal and facial acne.
• Fixed combinations: adapalene with benzoyl peroxide; tretinoin or adapalene with clindamycin.

Regimens.

• Acne: apply a pea-sized amount to the whole affected area (not spot treatment) once daily at night, 20 to 30 minutes after washing. Start every second or third night for 1 to 2 weeks and increase as tolerated. Response takes 8 to 12 weeks; continue as maintenance after other therapy has stopped.
• Photoageing and hyperpigmentation (melasma): tretinoin 0.025 to 0.05 percent nightly with daily sunscreen; triple combination (tretinoin, hydroquinone, mild steroid) for melasma for up to 8 to 12 weeks.
• Psoriasis (limited plaques): tazarotene 0.05 to 0.1 percent once daily at night, usually with a topical steroid.
• Children: adapalene from about 9 to 12 years in acne.

Selection. First-line topical acne treatment for comedonal and mild to moderate inflammatory acne, combined with benzoyl peroxide or a topical antibiotic. In darker skin, retinoids reduce post-inflammatory hyperpigmentation, but irritation can worsen it, so use low strengths, moisturisers and gradual titration.

Contraindications. Pregnancy and planned pregnancy for tazarotene (teratogenic); acute eczema or sunburn in the area; hypersensitivity.

Effects. Erythema, dryness, scaling, burning and a temporary flare in the first 2 to 4 weeks (retinoid dermatitis, easing with continued use); photosensitivity; rarely contact allergy.

Interactions. Avoid combining with other irritants (benzoyl peroxide at high strength with tretinoin at the same time, salicylic acid, abrasives); waxing is avoided on treated skin.

Monitoring. Review at 8 to 12 weeks; counsel on sunscreen and moisturiser.

Special groups. Pregnancy: tazarotene contraindicated; tretinoin and adapalene are avoided because of limited data, although absorption is very low. Breastfeeding: acceptable away from the nipple. Region: sun protection is necessary given high ultraviolet exposure.