Topical Retinoids — Viva

Q1: Classification and receptor pharmacology (3 min)

Examiner: Classify the topical retinoids. Which receptors do they act through?

Candidate: Four prescription generations. Tretinoin (1st, all-trans-retinoic acid, non-selective RAR-alpha/beta/gamma); tazarotene (2nd, acetylenic prodrug, RAR-beta/gamma); adapalene (3rd, naphthoic acid, RAR-beta/gamma selective, photostable); trifarotene (4th, RAR-gamma selective). They bind nuclear retinoic acid receptors (RAR) which heterodimerise with retinoid X receptors (RXR); the RAR-RXR complex binds retinoic acid response elements on DNA to modulate gene transcription. RAR-gamma is the predominant epidermal subtype (~90%), which is why trifarotene targets it.^[1]

Examiner: Why is adapalene preferred over tretinoin for acne?

^[5]Candidate: Three reasons: (1) photostable — does not degrade in UV, so can apply AM or PM; (2) least irritating — RAR-alpha-sparing reduces retinoid dermatitis; (3) benzoyl peroxide-compatible — BPO does not degrade adapalene, allowing fixed-dose Epiduo combination.^[2]

Q2: Mechanism of action (3 min)

Examiner: How do retinoids work in acne? And in photoaging?

Candidate: In acne, retinoids normalise follicular keratinocyte desquamation — they prevent the abnormal cohesion of keratinocytes at the follicular ostium that forms the microcomedone, the precursor of all acne lesions. This is comedolysis, the primary mechanism. They also have an anti-inflammatory effect: suppress neutrophil chemotaxis, downregulate TLR-2, reduce IL-1, IL-6, TNF-alpha. In photoaging, tretinoin stimulates dermal fibroblast collagen I and III synthesis and downregulates matrix metalloproteinases (MMP-1, MMP-3, MMP-9), partially reversing UV-induced collagen loss.^[1][2]

Examiner: What about the pigmentary effects?

Candidate: Retinoids accelerate epidermal turnover and inhibit melanosome transfer from melanocytes to keratinocytes, dispersing melanin. This is the basis for tretinoin in Kligman's triple-combination cream for melasma: hydroquinone + tretinoin + a corticosteroid. The retinoid both depigments and prevents oxidation of hydroquinone.^[1]

Q3: Pregnancy and safety (3 min)

Examiner: A patient on tazarotene discovers she is 6 weeks pregnant. What do you advise?

Candidate: Tazarotene is FDA Category X — an absolute contraindication in pregnancy. I would stop it immediately, document the timing and cumulative dose of exposure, and refer for obstetric counselling. The teratogenic phenotype is retinoic acid embryopathy: craniofacial defects (microtia, cleft palate), conotruncal cardiac defects, CNS abnormalities (hydrocephalus, microcephaly), and thymic aplasia. I would counsel that the systemic absorption from topical application is low and the absolute risk is much lower than with oral isotretinoin, but the pregnancy must be monitored. For acne management in pregnancy, I would switch to azelaic acid 15-20% or benzoyl peroxide, both of which are safe.^[1][3]

Examiner: What is required before starting tazarotene?

Candidate: A negative pregnancy test within 2 weeks of starting, reliable contraception during and for 1 month after treatment, and documented counselling. The same contraception requirement applies to oral retinoids. Tretinoin, adapalene, and trifarotene are Category C (avoid in pregnancy but no mandatory contraception protocol).^[1]

Q4: Side effects and management (3 min)

Examiner: A patient returns at 3 weeks with erythema, dryness, and peeling. What is this and how do you manage it?

Candidate: This is retinoid dermatitis — the expected irritant reaction that peaks at weeks 2-6 and resolves with continued use. Management depends on severity. Mild: reinforce moisturiser and the sandwich method (moisturiser-retinoid-moisturiser), and ensure correct technique — apply to DRY skin 20 min after washing, pea-sized amount, not wet skin. Moderate: reduce frequency to every other or every third night, or switch to a lower concentration or to adapalene (the least irritating retinoid). Severe with crusting or blistering: stop the retinoid, use cool compresses and a short course of mild topical corticosteroid, then reintroduce at the lowest concentration every third night. I would also check that she is not using concurrent irritants — AHAs, BHAs, astringents, or applying benzoyl peroxide at the same time as tretinoin.^[2]

Examiner: What if she also has an initial worsening of acne?

Candidate: That is the expected "purging" or retinisation — the retinoid brings deeper microcomedones to the surface as inflammatory papules in the first 2-4 weeks. I counsel her to persist; net improvement is visible at 8-12 weeks and maximum benefit at 3-6 months. If new deep nodules appear beyond 8 weeks at new sites, that is treatment failure, not purging, and warrants escalation to oral therapy.^[2]

Q5: Evidence and guidelines (2 min)

Examiner: What is the evidence for trifarotene?

Candidate: Trifarotene was approved by the FDA in October 2019 on the basis of the PERFECT 1 and PERFECT 2 phase 3 trials — two identical randomised controlled trials enrolling 2420 patients aged 9 and older with moderate facial and truncal acne. Trifarotene 0.005% cream was superior to vehicle for both facial acne and — uniquely among topical retinoids — truncal acne. It is the most receptor-selective retinoid, targeting RAR-gamma, the predominant epidermal subtype.^[4]

Examiner: And the guideline position?

Candidate: The American Academy of Dermatology 2024 guidelines position topical retinoids as foundational first-line therapy for acne at all severities — alone for comedonal acne, in combination with benzoyl peroxide and/or a topical antibiotic for inflammatory acne. Antibiotic stewardship is now central: limit antibiotic duration to 3-4 months and always combine with BPO to suppress Cutibacterium acnes resistance. After stopping oral antibiotics or isotretinoin, maintenance therapy with a topical retinoid plus BPO reduces relapse.^[3]

References5ShowHide

1. [1]Khalil S, Bardawil T, Stephan C, et al. Retinoids: a journey from the molecular structures and mechanisms of action to clinical uses in dermatology and adverse effects. Journal of Dermatological Treatment, 2017.PMID 28318351
2. [2]Kolli SS, Pecone D, Pona A, et al. Topical Retinoids in Acne Vulgaris: A Systematic Review. American Journal of Clinical Dermatology, 2019.PMID 30674002
3. [3]Reynolds RV, Yeung H, Cheng CE, et al. Guidelines of care for the management of acne vulgaris. Journal of the American Academy of Dermatology, 2024.PMID 38300170
4. [4]Tan J, Thiboutot D, Popp G, et al. Randomized phase 3 evaluation of trifarotene 50 microg/g cream treatment of moderate facial and truncal acne. Journal of the American Academy of Dermatology, 2019.PMID 30802558
5. [5]Bettoli V, Borghi A, Zauli S, et al. Maintenance therapy for acne vulgaris: efficacy of a 12-month treatment with adapalene-benzoyl peroxide after oral isotretinoin and a review of the literature Dermatology, 2013.PMID 24029411